FULL BLOOD COUNT: UNDERSTANDING FBC
Full blood count (FBC)
Called complete blood count (CBC) in the USA. Before the advent of modern haematology blood analysers the blood count consisted of a Hb concentration (estimated using a manual colorimetric technique), a white cell count and manual platelet count. Other parameters such as MCV had to be mathematically calculated (derived) using the measured variables Hb, RCC and PCV.
Modern analysers use a variety of methods to provide a huge range of FBC variables including electronic impedance, laser light scatter, light absorbance and staining characteristics. The resultant FBC provides measured variables such as Hb, PCV and RCC along with derived (mathematically) MCV, MCH and MCHC. These machines also provide automated platelet counts and a 5-part differential WBC.
Sample: peripheral blood EDTA; the sample should be analysed in the laboratory within 4h, if possible.
Main parameters measured
1. Hb concentration.
2. Red cell count (RCC).
3. MCV.
4. MCH.
5. MCHC.
6. Haematocrit (Hct) or PCV.
7. Red cell distribution width (RDW).
8. White cell count.
9. WBC differential.
10.Platelet count.
Some machines are even more sophisticated and will measure reticulocyte counts in addition to determination of reticulocyte Hb and MCV.
Role of the FBC
Why ask for a FBC? How will this aid the diagnosis or management of the patient? The FBC assesses several different parameters and can provide a great deal of information. The red cell variables will determine whether or not the patient is anaemic. If anaemia is present the MCV is likely to provide clues as to the cause of the anaemia. The white cells are often raised in infection—neutrophilia in bacterial infections and lymphocytosis in viral (but not always so). Platelets (size or number) may be abnormal either as a direct effect of underlying blood disease or may simply reflect the presence of some other underlying pathology. Most of us take a somewhat cursory glance at the FBC when the report arrives on the ward or in clinic, but a more detailed look may reveal a great deal more!
FBC parameters
Haemoglobin concentration (Hb)
Units: g/dL or g/L (Europe uses SI units; the USA still uses g/dL or
grams%).
MEDICAL ACRONYM: SYMBOLS AND ABBREVIATION
1° primary
2° secondary
A&E accident & emergency
AAFB acid and alcohol fast bacilli
Ab antibody
ABGs arterial blood gases
ACD anaemia of chronic disease
ACE angiotensin converting enzyme
ACh acetylcholine
ACL anticardiolipin antibody
ACR acetylcholine receptor
ACS acute coronary syndrome
ADA American Diabetes Association
ADH antidiuretic hormone
ADP adenosine 5-diphosphate
AECG ambulatory ECG
AF atrial fibrillation
Ag antigen
AIDS acquired immunodeficiency syndrome
AIHA autoimmune haemolytic anaemia
AKA alcoholic ketoacidosis
ALL acute lymphoblastic leukaemia
ALP alkaline phosphatase
ALT alanine aminotransferase
AMI acute myocardial infarction
AML acute myeloid leukaemia
ANA antinuclear antibodies
ANAE alpha naphthyl acetate esterase
ANCA antineutrophil cytoplasmic antibody
ANF antinuclear factor
APCR activated protein C resistance
APL antiphospholipid antibody
APML acute promyelocytic leukaemia
APS antiphospholipid syndrome
APTR activated partial thromboplastin time ratio
APTT activated partial thromboplastin time
ARF acute renal failure
AT (ATIII) antithrombin III
ATLL adult T cell leukaemia/lymphoma
ATP adenosine triphosphate
AXR abdominal x-ray
BBB blood–brain barrier
B-CLL B-cell chronic lymphocytic leukaemia
bd bis die (twice daily)
BJP Bence-Jones protein
BM bone marrow
BMJ British Medical Journal
BMT bone marrow transplant(ation)
BP blood pressure
Bx biopsy
C1 INH C1 esterase inhibitor
C3Nef complement C3 nephritic factor
C&S culture & sensitivity
Ca carcinoma
Ca2+ calcium
CABG coronary artery bypass graft
CAH congenital adrenal hyperplasia
cALL common acute lymphoblastic leukaemia
CBC complete blood count (American term for FBC)
CCF congestive cardiac failure
CCK cholecystokinin
CCU coronary care unit
CD cluster designation
cDNA complementary DNA
CEA carcinoembryonic antigen
CF cystic fibrosis or complement fixation
cfu colony-forming units
CGL chronic granulocytic leukaemia
CHAD cold haemagglutinin disease
CHD coronary heart disease
CJD Creutzfeldt-Jacob disease (v = new variant)
CK creatine kinase
CL– chloride
CLL chronic lymphocytic (‘lymphatic’) leukaemia
CLO test Campylobacter-like organism
CML chronic myeloid leukaemia
CMML chronic myelomonocytic leukaemia
CMV cytomegalovirus
CNS central nervous system
CO2 carbon dioxide
COPD chronic obstructive pulmonary disease
CPAP continuous positive airways pressure
CREST calcinosis, Raynaud’s syndrome, (o)esophageal motility
dysfunction, sclerodactyly and telangiectasia
CRF chronic renal failure
CRP C-reactive protein
CSF cerebrospinal fluid
CT computed tomography
CTLp cytotoxic T lymphocyte precursor assay
CVA cerebrovascular accident (stroke)
CVD cardiovascular disease
CVS cardiovascular system or chorionic villus sampling
CXR chest x-ray
DAT direct antiglobulin test
dATP deoxy ATP
DCCT Diabetes Control and Complications Trial
DCT direct Coombs’ test
DDAVP desamino D-arginyl vasopressin
DE evoked potential
DIC disseminated intravascular coagulation
DIDMOAD diabetes insipidus, diabetes mellitus, optic atrophy and
deafness
DKA diabetic ketoacidosis
dL decilitre
DM diabetes mellitus
DNA deoxyribonucleic acid
2,3-DPG 2,3-diphosphoglycerate
dRVVT dilute Russell’s viper venom test
DTT dilute thromboplastin time
DU duodenal ulcer
DVT deep vein thrombosis
DXT radiotherapy
EBV Epstein-Barr virus
ECG electrocardiograph
EDH extradural haemorrhage
EDTA ethylenediamine tetraacetic acid
EEG electroencephalogram
ELISA enzyme-linked immunosorbent assay
EMG electromyogram
Epo erythropoietin
ERCP endoscopic retrograde cholangiopancreatography
ESR erythrocyte sedimentation rate
ESREF end-stage renal failure
ET essential thrombocythaemia
etOH ethanol
FAB French–American–British
FACS fluorescence-activated cell sorter
FBC full blood count (aka complete blood count, CBC)
FDPs fibrin degradation products
Fe iron
FeSO4 ferrous sulphate
FISH fluorescence in situ hybridisation
FIX factor IX
fL femtolitres
FMRI functional MRI
FOB faecal occult blood
FPG fasting plasma glucose
FUO fever of unknown origin (like PUO)
FVIII factor VIII
FVL factor V Leiden
g gram
G&S group & save serum
GAD glutamic acid decarboxylase
GT -glutamyl transpeptidase
GBM glomerular basement membrane
GIT gastrointestinal tract
GPC gastric parietal cell
G6PD glucose-6-phosphate dehydrogenase
GPI general paralysis of the insane
GTN glyceryl trinitrate
GU gastric ulcer
GvHD graft versus host disease
h hour
HAV hepatitis A virus
Hb haemoglobin
HbA haemoglobin A ( 2 2)
HbA1c haemoglobin A1c
HbA2 haemoglobin A2 ( 2 2)
HbF haemoglobin F (fetal Hb, 2 2)
HbH haemoglobin H ( 4)
HBsAg hepatitis B surface antigen
HBV hepatitis B virus
hCG human chorionic gonadotrophin
HCO3
– bicarbonate
Hct haematocrit
HCV hepatitis C virus
HDN haemolytic disease of the newborn
HE hereditary elliptocytosis
HELLP haemolysis, elevated liver enzymes and low platelet
count
HIV human immunodeficiency virus
HLA human leucocyte antigen
HNA heparin neutralising activity
HONK hyperosmolar non-ketotic syndrome
HPA human platelet antigen
HPFH hereditary persistence of fetal haemoglobin
HPLC high-performance liquid chromatography
HPOA hypertrophic pulmonary osteoarthropathy
HPP hereditary pyropoikilocytosis
HTLV human T-lymphotropic virus
IAGT or IAT indirect antiglobulin test
IBS irritable bowel syndrome
ICA islet cell antibodies
ICH intracranial haemorrhage
IDA iron deficiency anaemia
IDDM insulin dependent (type 1) diabetes mellitus
IEF isoelectric focusing
IFG impaired fasting glucose
IFN- interferon alpha
IGT impaired glucose tolerance
IHD ischaemic heart disease
Ig immunoglobulin
IgA immunoglobulin A
IgD immunoglobulin D
IgE immunoglobulin E
IgG immunoglobulin G
IgM immunoglobulin M
IIF indirect immunofluorescence
IM intramuscular
INR international normalized ratio
ITP idiopathic thrombocytopenic purpura
ITU intensive therapy unit
iu/IU international units
IV intravenous
IVI intravenous infusion
IVU intravenous urogram
JCA juvenile chronic arthritis
JVP jugular venous pressure
K+ potassium
KCCT kaolin cephalin clotting time ( APTT)
kDa kiloDaltons
kg kilogram
KUB kidney, ureter, bladder (x-ray)
L litre or left
LA lupus anticoagulant or lactic acidosis or local anaesthetic
LAP leucocyte alkaline phosphatase (score)
LBBB left bundle branch block
LCM left costal margin
LDH lactate dehydrogenase
LFTs liver function tests
LIF left iliac fossa
LKM liver/kidney microsomal
LP lumbar puncture
LUQ left upper quadrant
LVF left ventricular failure
LVH left ventricular hypertrophy
MAG myelin-associated glycoprotein
MAIPA monoclonal antibody immobilisation of platelet antigens
MAOI monoamine oxidase inhibitor
MC&S microscopy, culture & sensitivity
MCH mean cell haemoglobin
MCHC mean corpuscular haemoglobin concentration
MCV mean cell volume
MDS myelodysplastic syndrome
MELAS myelopathy, encephalopathy, lactic acidosis and strokelike
episodes
mg milligram (10–3 gram)
MGUS monoclonal gammopathy of undetermined significance
MHC major histocompatibility complex
MI myocardial infarction
min minutes
MoAb monoclonal antibody
MODY maturity onset diabetes of the young
mOsm milliosmole
MPD myeloproliferative disease
MPV mean platelet volume
MRI magnetic resonance imaging
mRNA messenger ribonucleic acid
MS multiple sclerosis or mass spectroscopy
MSU mid-stream urine
MTP metatarsophalangeal
MUD matched unrelated donor (transplant)
μg microgram (10–6 gram)
Na+ sodium
NaCl sodium chloride
NADP nicotinamide adenine diphosphate
NADPH nicotinamide adenine diphosphate (reduced)
NAP neutrophil alkaline phosphatase
NEJM New England Journal of Medicine
NH3 ammonia
NHL non-Hodgkin’s lymphoma
NRBC nucleated red blood cells
NSAIDs non-steroidal anti-inflammatory drugs
NSTEMI non-ST-elevation myocardial infarction
OA osteoarthritis
OCP oral contraceptive pill
od omni die (once daily)
OGD oesophagogastroduodenoscopy
OGTT oral glucose tolerance test
OHCH Oxford Handbook of Clinical Haematology
OHCM Oxford Handbook of Clinical Medicine
PA posteroanterior or pernicious anaemia or pulmonary
artery
PACWP pulmonary artery capillary wedge pressure
PAD peripheral arterial disease
PAN polyarteritis nodosa
PaO2 partial pressure of O2 in arterial blood
PAS periodic acid-Schiff
PB peripheral blood
PBC primary biliary cirrhosis
PC protein C or provocation concentration
PCH paroxysmal cold haemoglobinuria
PCI percutaneous coronary intervention
PCL plasma cell leukaemia
PCP Pneumocystis carinii pneumonia
PCR polymerase chain reaction
PCT proximal convoluted tubule
PCV packed cell volume
PDA patent ductus arteriosus
PE pulmonary embolism
PEFR peak expiratory flow rate
PET positron emission tomography
Ph Philadelphia chromosome
PIFT platelet immunofluorescence test
PK pyruvate kinase
PO per os (by mouth)
PO3–
4 phosphate
PR per rectum
PRL prolactin
PRV polycythaemia rubra vera
PS protein S or Parkinson’s syndrome
PSA prostate-specific antigen
PT prothrombin time
PV plasma volume
qds quater die sumendus (to be taken 4 times a day)
RA refractory anaemia or rheumatoid arthritis
RAS renal angiotensin system or renal artery stenosis
RBBB right bundle branch block
RBCs red blood cells
RCC red blood cell count
RDW red cell distribution width
Rh Rhesus
RhF rheumatoid factor
RIA radioimmunoassay
RiCoF ristocetin cofactor
RIF right iliac fossa
RIPA ristocetin-induced platelet aggregation
RNP ribonucleoprotein
RPGN rapidly progressive glomerulonephritis
RT-PCR reverse transcriptase polymerase chain reaction
RUQ right upper quadrant
s seconds
SAECG signal-averaged ECG
SAH subarachnoid haemorrhage
SC subcutaneous
SCA sickle cell anaemia
SCD sickle cell disease
SDH subdural haemorrhage
SHBG sex-hormone-binding globulin
SLE systemic lupus erythematosus
SmIg surface membrane immunoglobulin
SOB short of breath
SOL space-occupying lesion
SM smooth muscle
SPECT single photon emission computed tomography
stat statim (immediate; as initial dose)
STEMI ST-elevation myocardial infarction
sTfR soluble transferrin receptor assay
SVC superior vena cava
SVCO superior vena caval obstruction
SXR skull x-ray
T° temperature
t1/2 half-life
T4 thyroxine
TA temporal arteritis
TB tuberculosis
tds ter die sumendum (to be taken 3 times a day)
TdT terminal deoxynucleotidyl transferase
TENS transcutaneous nerve stimulation
TFT thyroid function test(s)
TIAs transient ischaemic attacks
TIBC total iron binding capacity
TN trigeminal neuralgia
TNF tumour necrosis factor
TOE transoesophageal echocardiogram
TPA tissue plasminogen activator
TPO thyroid peroxidase
TRAB thyrotropin receptor antibodies
TRALI transfusion-associated lung injury
TRAP tartrate-resistant acid phosphatase
TSH thyroid-stimulating hormone
TT thrombin time
TTE transthoracic echocardiography
TTP thrombotic thrombocytopenic purpura
TXA tranexamic acid
u/U units
UC ulcerative colitis
U&E urea and electrolytes
UKPDS United Kingdom Prospective Diabetes Study
URTI upper respiratory tract infection
UTI urinary tract infection
USS ultrasound scan
VIII:C factor VIII clotting activity
VIP vasoactive intestinal peptide
Vit K vitamin K
VSD ventricular septal defect
VTE venous thromboembolism
vWD von Willebrand’s disease
vWF von Willebrand factor
vWFAg von Willebrand factor antigen
WBC white blood count or white blood cells
WHO World Health Organisation
WM Waldenström’s macroglobulinaemia
XDPs cross-linked fibrin degradation products
LUNG CANCER: UNDERSTANDING
This framework will be used to organize the material presented in this chapter.
Basics of Genetics and Molecular Biology Understanding oncology requires an integrated knowledge of the basics of molecular biology and genetics. While a general overview is provided here, more detailed descriptions should be sought in genetics textbooks. The central dogma of molecular biology holds that
cellular genetic information fl ows from DNA which undergoes replication, to RNA by the process of transcription and fi nally to proteins by the process of translation (Crick 1958). All of these steps are highly coordinated into a sequence of events known as the cell cycle. Of importance in lung cancer are alterations in the structure and transcription of DNA and subsequent disruption of critical processes associated with the cell cycle. DNA is a linear polymer of the four bases adenine (A), guanine (G), cytosine (C), and thymine (T) which defi ne the genetic code. These bases, which differ in their ring structure, are attached to an invariant backbone of deoxyribose sugars connected by phosphodiester bonds. Two strands of DNA hybridize to form a double helix through hydrogen bonding between bases, A to T and G to C (Watson
and Crick 1953). The double stranded DNA associates with accessory proteins such as histones which
package the long polymer into a stable form called chromatin (Laskey and Earnshaw 1980). For the
processes of replication and transcription to take place, the DNA must fi rst be uncoiled from the histones
to allow the appropriate molecular machinery to bind.
Genes, the most basic unit of inheritance, are coded by DNA. The linear sequence of the bases, in sets of
three, define each amino acid to be translated and hence, the structure of proteins. While there are over
three billion base pairs in the human genome, only approximately 1%–2% are coding, resulting in an
estimated 30,000–40,000 genes (Lander et al. 2001).
The structure of genes can be simplifi ed conceptually into two components, a coding region and a promoter
region. The promoter is a section of DNA upstream of the coding region which, in concert with other “enhancer” and “silencing” regions of DNA and numerous associated proteins, controls gene transcription. This regulation depends on a number of factors including cell type, extracellular signals, and stresses.
A particularly important method by which gene transcription is regulated in cancer is methylation
of the promoter region leading to gene silencing (Herman and Baylin 2003). In this process, termed
“epigenetics”, a cytosine that precedes a guanosine (CpG dinucleotide) in the DNA sequence is methylated.
While this can be a normal process utilized by the cell to inhibit transcription, abnormal levels of methyl cytosines have been observed in lung cancer cells. This aberrant transcriptional inhibition appears to play a signifi cant role in disruption of tumor suppressor genes and can act as one or both hits in Knudson’s (1971) two-hit hypothesis. The actual inhibition of transcription occurs as a result of the complex interplay of histones and proteins binding the methyl cytosines.
Another mechanism of gene alteration is inherited or de novo mutations in the DNA code. DNA
is damaged from a variety of sources including inherent instability, exposure to environmental and
toxic stresses, and a natural limit to its replicative accuracy, necessitating repair mechanisms to maintain
genetic integrity. The responsible DNA repair genes can be altered early in carcinogenesis leading
to a greater propensity for mutations (Ronen and Glickman 2001). Chromosomal rearrangements
also alter genes and are frequently seen in lung cancers. This process involves the exchange of
DNA from one chromosome to another and can lead to abnormal gene activation or aberrant coding regions. A target of many of the genetic changes noted in lung cancer is the cell cycle. The cell cycle is the
discrete states through which cells must pass for replication and is normally tightly regulated from
external and internal signaling. Lung cancer cells frequently acquire genetic changes which disrupt
the normal balance of positive and negative signals resulting in a variety of growth abnormalities. This
deregulation represents a fundamental change from normal cells.
The Hanahan and Weinberg framework is helpful in understanding how the current body of knowledge
regarding the molecular biology and genetics of lung cancer fi t into the observed disease process. Many
of the abnormalities and a summary of the different expression levels between lung cancer types is provided.
Self-Suffi cient Growth Signaling
In cancer, the tight growth control of normal cells is lost, allowing for continuous proliferation. The regular
homeostasis is disrupted as cells acquire the ability to both produce their own growth factors and increase
their sensitivity to exogenous ones. Key factors in these paracrine and autocrine loops are encoded by
proto-oncogenes, many of which are activated in lung cancer. Proto-oncogenes encode proteins important
for normal cell growth and are called oncogenes only after becoming abnormally activated. This activation,
usually a result of point mutations or chromosomal translocations, leads to gain-of-function effects for
the cell. Several well studied families of oncogenes have been identifi ed in lung cancer including RAS,
MYC, and ERB-B. Ras:
The RAS family of oncogenes, including H-, K-, and N-RAS, encode a 21-kDa protein acting at the
cytoplasmic cell membrane as a guanosine-associated switch. The protein is associated with receptor
tyrosine kinases (RTKs) and plays a pivotal role in transducing extracellular signals to numerous growth
signaling pathways. Ras is activated by binding guanosine triphosphate (GTP), a process accomplished
by associated proteins; hydrolysis of this GTP to guanosine diphosphate inactivates Ras. Once active, Ras
activates multiple effector molecules including components of the following pathways: Raf-MAPK, PI3KAkt, and Rac-Rho (Shields et al. 2000).
K-RAS is mutated in 25% of non-small cell lung cancer (NSCLC), with rates highest in adenocarcinoma
at 30%–50%, and lowest in squamous cell at 0%–5% (Graziano et al. 1999). The mutations in
K-RAS are usually in codons 12, 13, and 61 and have been associated with frequent G-T transformations
linked to polycyclic hydrocarbons found in cigarette smoke (Rodenhuis and Slebos 1992). While a common
occurrence in NSCLC, mutations in RAS are not seen in small cell lung cancer (SCLC) (Wistuba et
al. 2001). Although results have been mixed, K-RAS mutational status appears to be related to prognosis
in NSCLC. Early studies found shortened diseasefree and overall survival for patients with K-RAS
point mutations (Slebos et al. 1990). Subsequent studies did not consistently fi nd this relationship but
on meta-analysis an increased risk of worsened 2-year survival was noted (Huncharek et al. 1999). A
possible explanation for this relationship is that mutated RAS appears to confer treatment resistance to
cancer cells. Its role in chemotherapeutic resistance is unclear but there is a growing body of evidence
showing the importance of the Ras pathway in radiation resistance. In vitro studies have demonstrated
increased radiation resistance in cell lines expressing mutant RAS (Sklar 1988). Therapeutics have been
developed which inhibit the activation of Ras and lead to reversal of radiation resistance in studies in
vivo (Cohen-Jonathan et al. 2000). The mechanism for the radiation resistance is still unclear but may
relate to activation of signals downstream of Ras such as phosphoinositide 3-kinase (PI3K) or Rho
(Lebowitz and Prendergast 1998).
Akt: Akt is a protein kinase downstream of PI3K in a growth signaling pathway. It is activated by many
growth signals including insulin-like growth factor (IGF) and Ras activation. Once activated, Akt plays
a role in progression through the cell cycle and cell survival. Akt is inactivated by PTEN, a protein frequently
mutated or epigenetically inhibited in lung cancer (Soria et al. 2002). Akt is constitutively activated
at high rates in both NSCLC (70%–90%) and Molecular Abnormalities in Lung Cancer.
SCLC (65%) and is associated with chemotherapeutic and radiation resistance in SCLC cell lines (Kraus et
al. 2002). Myc: The MYC oncogenes, c-, N-, and L-, encode DNA-binding proteins associated with transcriptional regulation. The activity of the Myc protein is regulated through homo- and heterodimerization
(Henriksson and Luscher 1996). When Myc is bound to the protein Max for example, it activates
transcription of cell cycle checkpoint proteins such as Cdc25A which promote cell replication (Santoni-
Rugiu et al. 2000). Similarly, inhibition of Myc occurs through heterodimerization with proteins such
as Mad. MYC activation occurs through dysregulated expression of the normal gene (Krystal et al. 1988).
Overexpression is seen in approximately 20%–60% of NSCLC and 30% of SCLC (Gazzeri et al. 1994).
In SCLC, Myc overexpression has been linked to cell lines treated with chemotherapeutics suggesting a
response mechanism. Additionally, overexpression of MYC is associated with worsened prognosis in SCLC
but not NSCLC. In vitro studies indicate that while v-Myc expression alone does not affect radiation resistance, when coexpressed with H-Ras, there is synergistically increased radioresistance compared to Ras expression alone (McKenna et al. 1990).
Receptor tyrosine kinases: The ERB-B family of transmembrane RTKs include epidermal growth
factor receptor (EGFR or ERB-B1) and HER2/neu (ERB-B2). When bound to ligands, these proteins
homo- or heterodimerize, becoming activated. The downstream effectors of the receptors include Ras
and mitogen-activated protein kinase (MAPK) leading to various processes including cell growth and
proliferation. Ligands are produced exogenously as well as from the cancer cells themselves, creating selfactivating loops.
Overexpression of EGFR is seen in 50% of NSCLC, with the highest rate (80%) noted in squamous cell.
Higher expression appears to predict a slightly worsened survival for those with NSCLC (Meert et al.
2002). Increased expression of HER2/neu is seen in 30% of both NSCLC and SCLC and appears in both
cases to predict worsened survival (Meert et al. 2003; Potti et al. 2002). The worsened prognosis may be a
result of chemotherapeutic resistance but this is still unclear. EGFR is known to be an upstream regulator
of the PI3K-Akt pathway, possibly through Ras, and thus may play a role in radioresistance (Gupta
et al. 2002). Similarly, cells overexpressing HER2/neu have been shown to be radioresistant (Pietras et al.
1999).
Another RTK highly expressed (50%) in SCLC is c-Kit. This receptor is frequently coexpressed with its
ligand, stem cell factor, leading to stimulated growth. As with EGFR and HER2/neu, c-Kit represents a potential target for therapy.
Other factors: Neuropeptides act as both neurotransmitters in the central nervous system and
as endocrine factors in non-neurologic tissue. The family of bombesin-like peptides includes gastrin-
releasing peptide (GRP) and neuromedin B (NMB). SCLC cells have been shown to synthesize
and secrete these factors which function in a complex system of neuropeptide induced cell growth
(Heasley 2001). Other growth factors such as IGF, found to be elevated in ~90% of NSCLC and SCLC,
have been shown to play a role in carcinogenesis and are associated with an increased risk of acquiring
lung cancer (Yu et al. 1999). Interestingly, overexpression of the IGF receptor has been shown to induce radiation resistance in vitro (Macaulay et al. 2001).
Insensitivity to Antigrowth Signals
The growth of normal cells is kept in check by antigrowth signals, many of which are encoded by tumor
suppressor genes (TSGs). The loss of one allele either through inheritance or damage and the second
through damage from mutation or epigenetics, leads to complete loss of function of these factors. When
intact, many of the proteins encoded by these genes exert their control through regulation of the cell cycle.
The ability to evade the inherent checkpoints of this system gives the cell the capacity to grow without
inhibition. While important antigrowth pathways such as p16(INK4A)-RB have been studied in lung
cancer, other TSGs and their roles are just beginning to be evaluated.
RB: The RB1 gene located on chromosome 13q14.11 was identifi ed initially in retinoblastoma
but has been subsequently identifi ed in many human cancers including lung. The RB protein plays a pivotal
role in inhibiting G1/S transition via the E2F family of transcription factors. RB inhibits transcriptional
activation by binding E2F. As the cell progresses from G1 to the S phase, RB becomes increasingly hyperphosphorylated in which state it disassociates from the E2F. Once unbound, the E2F can induce transcription of genes necessary for normal DNA synthesis.
Evasion of Programmed Cell Death
The process of programmed cell death, apoptosis, occurs in cells throughout the body in response to
various signals. This stereotyped process involves a cascade of signals from cell surface receptors and
internal monitoring processes to effector proteins which act on the mitochondria and nucleus to kill the
cell. Signals that induce apoptosis include activation of oncogenes, DNA damage, absence of stroma–cell
and cell–cell interactions, and hypoxia. Apoptosis is important in cancer because the tumor’s rate of
growth is determined not only by the constituent cells’ ability to replicate but also the attrition rate of
those same cells. In addition, the end result of many cancer therapies is apoptosis and treatment resistant
cells have frequently developed mechanisms to evade this fate.
PRIMARY ALDOSTERONISM: CAUSE AND ASSESSMENT
Nonsuppressible (primary) hypersecretion of aldosterone is an uncommon but underdiagnosed cause of hypertension. The classic presenting signs of primary aldosteronism are hypertension and hypokalemia.
Primary aldosteronism refers to excessive secretion of aldosterone by the adrenal cortex, which is usually caused by a cortical adenoma (tumor) or bilateral adreanal hyperplasia. Hyperaldosteronism, in turn, causes excessive sodium and water retention and excessive potassium excretion by the kidneys and GI tracts. A secondary form of the disease occurs in conjuction with heart failure, renal dysfunction, or cirrhosis of the liver. One to 2 percent of cases of hypertension are caused by primary aldosteronism, which can be treated by adrenalectomy.
Severity percent of patients wit haldosterone-secreting adenomas are women, and the incidence of primary aldosteronism is four times higher among blacks than among the general population. Complications include the long-term effects of untreated hypertension - stroke, renal failure, and heart failure.
Many subtypes of primary aldosteronism have been described since Conn's original report of the aldosterone-producing adenoma in 1954. The most common subtypes are:
- Aldosterone-producing adenomas
- Bilateral idiopathic hyperaldosteronism
Assessment:
1. Excessive thirst (polydipsia) caused by hypermatremia
2. Muscle weakness caused by hypokalemia.
3. Possible paresthesias, tetany, and polyria caused by alkalosis
4. Hypertension.
Less common forms include:
- Unilateral hyperplasia or primary adrenal hyperplasia (caused by micronodular or macronodular hyperplasia of the zona glomerulosa of predominantly one adrenal gland)
- Familial hyperaldosteronism type I (glucocorticoid-remediable aldosteronism) and type II (the familial occurrence of aldosterone-producing adenoma or bilateral idiopathic hyperplasia or both)
- Pure aldosterone-producing adrenocortical carcinomas and ectopic aldosterone-secreting tumors (eg, neoplasms in the ovary or kidney)
- The subtype-directed treatment of primary aldosteronism will be reviewed here. The clinical manifestations and diagnosis of this disorder and other, less common causes of mineralocorticoid excess are discussed separately.
GOALS OF THERAPY — The treatment goal is to prevent the morbidity and mortality associated with hypertension, hypokalemia, and cardiovascular damage. The cause of primary aldosteronism helps to determine the appropriate treatment. Normalization of blood pressure should not be the only goal. In addition to the kidney and colon, mineralocorticoid receptors occur in the heart, brain, and blood vessels. Excessive secretion of aldosterone is associated with increased risk of cardiovascular disease and morbidity [2-4]. Therefore, normalization of circulating aldosterone or mineralocorticoid receptor blockade should be part of the management plan for all patients with primary aldosteronism.
GENERAL PRINCIPLES — Establishing the correct subtype diagnosis is essential since the treatment of primary aldosteronism is based upon whether the adrenal aldosterone hypersecretion is unilateral (adenoma, unilateral hyperplasia, or carcinoma) or bilateral (idiopathic adrenal hyperplasia or glucocorticoid-remediable aldosteronism).
Surgery is curative only in patients with unilateral disease.
Patients with bilateral idiopathic adrenal hyperplasia are treated with a mineralocorticoid antagonist.
Patients with glucocorticoid-remediable aldosteronism should receive physiologic doses of a glucocorticoid.
Clinical Guidelines — In 2008, The Endocrine Society published evidence-based guidelines for the diagnosis and treatment of primary aldosteronism [5]. Our therapeutic approach outlined here is consistent with the guidelines. The recommendations for case detection and confirmation of primary aldosteronism are reviewed separately.
UNILATERAL ADRENAL ADENOMA OR HYPERPLASIA — A unilateral adrenal adenoma is responsible for the hypersecretion of aldosterone in 30 to 60 percent of cases of primary aldosteronism [2], while unilateral hyperplasia is less common (about 3 percent). Surgery is the preferred therapy in this setting. An alternative is medical therapy with a mineralocorticoid receptor antagonist.
Surgery — Unilateral adrenalectomy in patients with aldosterone-producing adenomas or unilateral hyperplasia induces a marked reduction in aldosterone secretion and correction of the hypokalemia in almost all patients. Hypertension is improved in all and is cured in approximately 35 to 60 percent of patients.
We suggest laparoscopic adrenalectomy over open adrenalectomy because it is associated with shorter hospital stays and fewer complications.
Laparoscopic partial adrenalectomy (removal of an adenoma leaving the remaining adrenal intact) has been tried as a strategy to further reduce surgical morbidity, but it is an inadequate procedure in many cases. This was illustrated in a series of 92 patients with primary aldosteronism undergoing laparoscopic adrenalectomy [13]. Postoperatively, all 63 patients with total adrenalectomy had improved blood pressure and normal plasma aldosterone, while 2 of 29 with partial adrenalectomy had persistent hypertension and high plasma aldosterone. Of the 63 removed adrenal glands, 17 (27 percent) contained multiple nodules along with what was thought to be the hypersecretory adenoma. Thus, we suggest resection of the entire affected adrenal gland.
Preoperatively, hypertension should be controlled and hypokalemia should be corrected with a mineralocorticoid receptor antagonist (eg, spironolactone or eplerenone). The blood pressure response to spironolactone preoperatively often predicts the blood pressure response to unilateral adrenalectomy in patients with aldosterone-producing adenomas.
Postoperative management — Postoperative management after unilateral adrenalectomy should include the following:
Plasma aldosterone should be measured the day after surgery to assess for cure.
Potassium supplements and spironolactone should be discontinued, and, if possible, antihypertensive therapy should be decreased.
Patients should be monitored closely for hyperkalemia, which may result from transient hypoaldosteronism due to chronic suppression of renal renin release and contralateral adrenal gland aldosterone secretion. Serum potassium should be measured during the hospitalization, and as an outpatient, once weekly for four weeks. Occasionally short-term supplementation with fludrocortisone may be needed to treat the hyperkalemia.
Serum creatinine should be followed serially in patients who had renal insufficiency preoperatively. Primary aldosteronism has been associated with renal toxicity [14-16], and improvement of hypertension corrects renal hyperfiltration and may unmask the renal damage. In a long-term study that included 50 patients with primary aldosteronism and 100 patients with essential hypertension, during 30 to 90 days after intervention, the mean glomerular filtration rate decreased in patients with primary aldosteronism by -13.6 mL/min, but only by -2.1 mL/min in patients with essential hypertension, despite similar blood pressure values.
The preferred intravenous fluid after surgery is isotonic saline without potassium (unless the patient is still hypokalemic) and a sodium-rich diet should be suggested after discharge.
Effect on hypertension — Although hypertension is cured in some patients, a lesser degree of hypertension persists in as many as 40 to 65 percent of cases. A number of clinical features help to identify patients who are more likely to experience complete resolution of their hypertension after adrenalectomy, including lack of family history of hypertension, shorter duration of hypertension, preoperative use of two or fewer antihypertensive agents, younger age, higher preoperative ratio of plasma aldosterone concentration to plasma renin activity, and higher urine aldosterone level.
Persistent hypertension may be related to underlying essential hypertension and/or the development of nephrosclerosis after a prolonged period of uncontrolled hypertension. It is also possible that an error in subtype assignment has been made and that the patient has bilateral adrenal hyperplasia, a disorder that should be treated medically, not with unilateral adrenalectomy. As many as one-third of patients thought to have a unilateral lesion on imaging studies have bilateral adrenal hyperplasia on adrenal vein sampling.
A scoring system, the aldosteronoma resolution score (ARS), has been proposed to help identify patients at low or high likelihood of complete resolution of hypertension after adrenalectomy. In a study of 100 patients with primary aldosteronism seen at a single tertiary center, four clinical features provided the best predictive model for complete resolution of hypertension after adrenalectomy. For scoring purposes, each predictor was assigned a weight as follows:
Two or fewer antihypertensive medications (2 points)
Body mass index ≤25 kg/m2 (1 point)
Duration of hypertension ≤6 years (1 point)
Female sex (1 point)
The likelihood of complete resolution of hypertension for patients with ARS scores of 0 to 1, 2 to 3, and 4 to 5 was 27, 46, and 75 percent, respectively. These relationships were validated in a second population of 67 patients from a different tertiary center. Thus, the ARS appears to be a useful tool for informing patients of the likelihood of resolution of hypertension after surgery.
Ablative procedures — Although published data are limited, some centers have advocated percutaneous ablative therapy for unilateral adrenal adenomas, including percutaneous acetic acid injection and radiofrequency ablation.
Percutaneous ablative therapy requires overnight hospitalization. It is also associated with a variety of adverse effects, including abdominal pain, hematuria, pancreatitis, pneumothorax, bleeding, adrenal abscess formation, tumor tracking, and incomplete ablation.
Given the limited experience, uncertain success rate, and potential complications, we cannot recommend adrenal percutaneous ablative therapy.
Medical therapy
Aldosterone antagonists — Although laparoscopic adrenalectomy is more cost-effective over time, the administration of an aldosterone (mineralocorticoid receptor) antagonist is an effective alternative in patients who refuse or are not candidates for surgery. The efficacy of this approach was illustrated in a study of 24 patients with adenomas who were treated medically for at least five years. The following results were reported:
Systolic and diastolic blood pressures decreased from 175/106 to 129/79 mmHg.
The serum potassium concentration increased from 3.0 to 4.3 mEq/L.
Five tumors had increased in size by at least 0.5 cm (as determined by CT scan), but there was no evidence of malignant transformation in any patient.
Dietary sodium restriction (<100 mEq/day), maintenance of ideal body weight, avoidance of alcohol, and regular aerobic exercise contribute to the success of pharmacologic therapy in almost any patient with hypertension.
There have been no placebo-controlled, randomized trials evaluating the relative efficacy of different drugs in the management of primary aldosteronism. Spironolactone has long been the drug of choice; eplerenone represents a newer more expensive alternative with fewer side effects. (See 'Suggested approach' below.)
There are some precautions with the use of spironolactone:
Serum potassium and creatinine should be monitored frequently during the first four to six weeks of therapy, especially in patients with renal insufficiency or diabetes mellitus. The clinical course and circumstances dictate the frequency of subsequent monitoring.
Spironolactone may increase the half-life of digoxin, and for patients taking this drug, the dose may need to be adjusted when treatment with spironolactone is started.
Concomitant therapy with salicylates or nonsteroidal antiinflammatory drugs may interfere with the antihypertensive efficacy of spironolactone (and other antihypertensive medications).
Spironolactone is also a progesterone agonist and androgen receptor antagonist, resulting in side effects such as breast tenderness and menstrual irregularities in women, and impotence, decreased libido, and gynecomastia in men. In a review of 699 patients with primary aldosteronism treated with spironolactone, the incidence of gynecomastia was dose-dependent: 6.9 percent at doses below 50 mg/day and 52 percent at doses above 150 mg/day. Spironolactone may also be associated with minor gastrointestinal symptoms.
Eplerenone is a highly selective mineralocorticoid receptor antagonist. Compared to spironolactone, eplerenone has 0.1 percent of the binding affinity to androgen receptors and less than 1 percent of the binding affinity to progesterone receptors.
Because of its selectivity, eplerenone is associated with a low incidence of endocrine side effects. Eplerenone would be considered the first-line drug over spironolactone if it provided the same degree of blood pressure and potassium control with fewer side effects. However, trials comparing spironolactone and eplerenone in patients with primary aldosteronism have not been published. In addition, eplerenone is substantially more expensive. Thus, until more data become available, it is reasonable to start with spironolactone and, if endocrine side effects are limiting, switch to eplerenone.
For patients with primary aldosteronism, a reasonable starting dose of eplerenone is 25 mg once or twice daily and titrated upward for normokalemia without the aid of potassium supplements. The maximum dose approved by the US Food and Drug Administration for hypertension is 100 mg daily. Eplerenone has 25 to 50 percent less mg per mg potency than spironolactone. Serum potassium and creatinine should be monitored frequently during the first four to six weeks of therapy, especially in patients with renal insufficiency or diabetes mellitus. The clinical course and circumstances dictate the frequency of subsequent monitoring. Eplerenone is now available as a generic, but it remains substantially more expensive than spironolactone.
Potassium-sparing diuretics — Potassium-sparing diuretics that block the aldosterone-sensitive sodium channel in the collecting tubules (amiloride, triamterene) can block the renal effects of aldosterone, lowering the blood pressure and raising the serum potassium concentration. However, these drugs are not recommended for first-line therapy because of persistence of hyperaldosteronism with its possible deleterious cardiovascular effects. (See "Clinical features of primary aldosteronism", section on 'Cardiovascular risk' and "Mechanism of action of diuretics", section on 'Potassium-sparing diuretics'.)
Suggested approach — The goals of medical therapy in patients with unilateral disease who refuse or are not candidates for surgery are correction of hypokalemia, restoration of normal blood pressure, and reversal of the effects of hyperaldosteronism on the heart.
When using spironolactone or, if not tolerated, eplerenone, we suggest the following regimen, which is consistent with the 2008 Endocrine Society guidelines.
Spironolactone is titrated to a normal serum potassium concentration without the aid of potassium supplements. The starting dose is 12.5 to 25 mg daily with food, which increases drug absorption. The dose can be increased every two weeks.
The blood pressure goal is often difficult to achieve with monotherapy, since a lesser degree of hypertension persists after surgery in as many as 40 to 65 percent of patients despite complete correction of the hyperaldosteronism. (See 'Effect on hypertension' above.) If hypertension persists, we add another antihypertensive drug (eg, 12.5 to 25 mg of hydrochlorothiazide or chlorthalidone daily). Amiloride is an alternative for men and women intolerant of both spironolactone and eplerenone. Amiloride dosing may be started at 5 mg twice daily and increased to the dose needed to correct the hypokalemia. If the hypertension persists, a second-step drug should be added. Low doses of a thiazide diuretic (eg, 12.5 to 25 mg of hydrochlorothiazide or chlorthalidone daily) are preferred because hypervolemia is a major reason for resistance to amiloride.
Monitoring — With each medication change, it is important to monitor the effect on both blood pressure and serum potassium. Serum potassium, creatinine, and blood pressure should be monitored frequently during the first four to six weeks of medical therapy (especially in patients with renal insufficiency or diabetes mellitus). Clinical course and circumstances dictate the frequency of monitoring thereafter.
BILATERAL ADRENAL HYPERPLASIA — There are two forms of primary aldosteronism due to bilateral adrenal zona glomerulosa hyperplasia: idiopathic adrenal hyperplasia and the rare glucocorticoid-remediable aldosteronism, which responds to the administration of exogenous glucocorticoid. (See "Approach to the patient with hypertension and hypokalemia" and "Glucocorticoid-remediable aldosteronism".)
Idiopathic adrenal hyperplasia — Idiopathic adrenal hyperplasia is generally a milder disease than adrenal adenoma, with less hypersecretion of aldosterone and less hypokalemia. Such patients should be treated with an aldosterone (mineralocorticoid receptor) antagonist.
Subtotal adrenalectomy has been tried in patients with idiopathic hyperplasia, but only a minority of patients have a clinically significant hypotensive response. However, unilateral adrenalectomy in patients with bilateral adrenal hyperplasia does have the potential to effectively "debulk" the amount of adrenal tissue responsible for aldosterone hypersecretion and may, in selected patients, provide improved blood pressure control.
Optimal treatment of idiopathic adrenal hyperplasia consists of mineralocorticoid receptor blockade with spironolactone or eplerenone as described above for medical therapy of a unilateral adrenal adenoma. The goals of therapy are the same as for unilateral adenoma: normalization of the serum potassium in hypokalemic patients, normalization of the blood pressure, and reversal of the effects of hyperaldosteronism on the heart (which cannot be confirmed clinically).
In patients with bilateral adrenal hyperplasia, quality of life (QOL), as measured by the validated Medical Outcomes Study Short Form 6 General Health Survey (SF-36), improves during treatment with mineralocorticoid receptor antagonists [31]. However, the improvement appears to be more modest and occurs more slowly when compared to historical control patients undergoing unilateral adrenalectomy for unilateral adrenal adenoma.
A thiazide diuretic or an angiotensin converting enzyme (ACE) inhibitor can be added if the hypertension persists. The efficacy of an ACE inhibitor in the low plasma renin state may in part reflect the role of even low concentrations of angiotensin II as an aldosterone secretagogue in adrenal hyperplasia.
Glucocorticoid-remediable aldosteronism — Before initiating treatment for glucocorticoid-remediable aldosteronism, the diagnosis should be confirmed with genetic testing; the mutation in patients with GRA is fusion of the promoter region of the gene for CYP11B1 and the coding sequences of CYP11B2.
Chronic treatment with physiologic doses of a glucocorticoid normalizes blood pressure and corrects hypokalemia. The clinician should be cautious about inducing iatrogenic Cushing's syndrome with excessive doses of glucocorticoids, especially with the use of dexamethasone in children.
SUMMARY AND RECOMMENDATIONS
From a treatment perspective, the two major forms of primary aldosteronism are: unilateral adrenal aldosterone hypersecretion (eg, adenoma, unilateral hyperplasia, or carcinoma) and bilateral aldosterone hypersecretion (eg, idiopathic adrenal hyperplasia and the rare glucocorticoid-remediable aldosteronism).
The goals of therapy for primary aldosteronism due to either unilateral or bilateral adrenal disease are the same and include normalization of the serum potassium in hypokalemic patients, normalization of the blood pressure, which often persists after correction of the hyperaldosteronism, and reversal of the adverse cardiovascular effects of hyperaldosteronism.
For most patients with confirmed unilateral aldosterone hypersecretion (eg, adrenal adenoma or unilateral adrenal hyperplasia), we suggest unilateral adrenalectomy over medical therapy (Grade 2B).
Because of the reduction in postoperative morbidity, hospital stay, and expense compared with open laparotomy, we suggest laparoscopic adrenalectomy by an experienced endocrine surgeon for adrenal adenomas (Grade 2C). Hypokalemia should be corrected with spironolactone preoperatively.
We recommend that most patients with bilateral adrenal hyperplasia be treated with medical therapy, not adrenalectomy (Grade 1B). Blood pressure control is often inadequate with subtotal adrenalectomy, and the risks associated with bilateral adrenalectomy (including the need for lifelong glucocorticoid and mineralocorticoid replacement) outweigh the potential benefits.
For patients with either bilateral adrenal hyperplasia or confirmed unilateral adrenal aldosterone hypersecretion (who refuse or are not candidates for surgery), we recommend an aldosterone antagonist (eg, spironolactone or eplerenone) over other potassium-sparing diuretics (eg, amiloride, triamterene) as our first choice for pharmacologic therapy (Grade 1C).
Of the aldosterone antagonists, we suggest spironolactone as the first line drug (Grade 2C) and switch to eplerenone if side effects are limiting. Eplerenone is a more selective mineralocorticoid receptor antagonist than spironolactone, and may be associated with fewer side effects. However, it is more expensive, and there are no clinical trial data comparing efficacy.
For patients who do not tolerate spironolactone or eplerenone, we switch to a potassium-sparing diuretic, such as amiloride.
Serum potassium, creatinine, and blood pressure should be monitored frequently during the first four to six weeks of medical therapy (especially in patients with renal insufficiency or diabetes mellitus). Clinical course and circumstances dictate the frequency of monitoring thereafter.
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