Tumor and Cardiac Markers

Most tumor and cardiac markers are proteins measured by immunoassay. Serial change is usually more informative than a single result, and results from different manufacturers’ assays are not interchangeable. Predictable assay failures can also produce misleading values. Tumor markers usually monitor an established malignancy, whereas cardiac markers help distinguish myocardial injury from its mimics within hours. Interpretation depends on marker kinetics and assay interference.¹

Limits of tumor markers

A tumor marker is a blood- or tissue-based biomarker elevated in association with cancer and produced by a tumor or by host tissue responding to it. No available marker is simultaneously tumor-specific, absent in health, and reliably detectable. Tumor markers are used for targeted screening in defined at-risk groups, to support diagnosis, and for prognosis, therapy monitoring, and recurrence detection. They are not intended for population-wide screening. Major classes include oncofetal antigens, hormones and hormone metabolites, carbohydrate and monoclonal-antibody-defined antigens, enzymes, and receptors.¹

Oncofetal antigens

Oncofetal antigens are proteins expressed during fetal development, silenced in mature tissue, and re-expressed by tumors.

α-Fetoprotein (AFP) is a 70-kD albumin-related fetal transport protein with an adult reference range typically below 10 to 15 ng/mL, depending on the method. AFP may be elevated in hepatocellular carcinoma and in nonseminomatous testicular germ-cell tumors, but pregnancy and nonmalignant liver disease also raise it. AFP alone is not diagnostic of hepatocellular carcinoma. Current hepatology guidance uses AFP with liver ultrasound for surveillance of at-risk patients. Diagnosis rests on characteristic multiphasic imaging or pathology, while AFP supports treatment and recurrence monitoring.^1,2

Carcinoembryonic antigen (CEA) is a glycoprotein of roughly 200 kD in the immunoglobulin superfamily, used chiefly to monitor colorectal cancer. It also rises in lung, breast, and other gastrointestinal malignancies, and it is nonspecific at every concentration, so it should not be used to diagnose malignancy. In known colorectal cancer, serial results support prognosis and treatment or recurrence monitoring.¹

AFP and human chorionic gonadotropin (hCG) together help classify testicular germ-cell tumors:¹

Hormones and hormone metabolites

hCG is a 45-kD dimeric placental hormone elevated in trophoblastic tumors and in germ-cell tumors of the ovary and testis. It is the principal marker for gestational trophoblastic disease, in which concentrations often exceed 100,000 mIU/mL, far above those of normal pregnancy. hCG circulates as intact hormone, free β-subunit, and degradation fragments; a total β-hCG assay detects both the intact hormone and the free β-subunit, so the assay’s specificity for these forms shapes the result.¹

Endocrine hormones mark their secreting tumors directly: calcitonin for medullary thyroid carcinoma, ACTH for ectopic ACTH-producing tumors, gastrin for gastrinoma and Zollinger-Ellison syndrome, growth hormone for pituitary adenoma with acromegaly, cortisol for adrenal tumors and Cushing syndrome, PTH for parathyroid adenoma, and prolactin for prolactinoma. Antidiuretic hormone, or its surrogate copeptin, is used in water-balance evaluation. Inappropriate secretion may be ectopic, classically from small-cell lung cancer, but ADH is not a standard marker for posterior-pituitary tumors.¹

Homovanillic acid (HVA) and vanillylmandelic acid (VMA) are catecholamine metabolites measured by HPLC in 24-hour urine that support the diagnosis of neuroblastoma. Fractionated metanephrines in 24-hour urine or plasma support evaluation for pheochromocytoma and paraganglioma. 5-Hydroxyindoleacetic acid (5-HIAA), a serotonin metabolite, supports the diagnosis of carcinoid tumors.¹

Carbohydrate and monoclonal-antibody-defined antigens

Monoclonal antibodies raised against tumor material defined a family of carbohydrate epitopes, and each marker takes its name from the antibody that defined it.¹

Enzyme, protein, and receptor markers

Prostate-specific antigen (PSA) is a 28-kD serine protease of the kallikrein family produced by prostatic epithelium. It circulates free and bound, mostly to α₁-antichymotrypsin. Benign prostatic hyperplasia and prostatitis also raise PSA, and a lower free-PSA fraction is more suggestive of malignancy.¹

Neuron-specific enolase (NSE), the γ-isoenzyme of enolase concentrated in neuroendocrine tissue, is an auxiliary marker for small-cell lung carcinoma, carcinoid tumors, pancreatic islet-cell tumors, and neuroblastoma, with a reference range below 15 ng/mL. Erythrocytes also contain enolase, so a hemolyzed specimen is rejected.¹

Serum free light chains, κ and λ with their κ:λ ratio, monitor monoclonal plasma-cell disorders. They are particularly useful in nonsecretory or oligosecretory myeloma, which produces too little intact immunoglobulin for reliable detection by serum or urine protein electrophoresis.¹

Human epididymis protein 4 (HE4), a protein of unknown function overexpressed in ovarian carcinoma, is used with CA-125 in the Risk of Ovarian Malignancy Algorithm (ROMA) to evaluate a pelvic mass. HE4 can improve specificity over CA-125 alone because benign conditions such as endometriosis raise CA-125 but not HE4. The laboratory must apply the assay manufacturer’s validated, menopause-specific HE4 and ROMA decision limits in the manufacturer’s stated units; on a platform that reports ROMA as a percentage, prediction-index values must not be substituted and the decimal point must not be moved.¹

β₂-Microglobulin is a nonspecific marker of cellular turnover with prognostic value in lymphoproliferative disorders. It also rises with reduced glomerular filtration, so renal function shapes its interpretation.¹

Tissue receptors are measured on tumor tissue rather than in serum. Estrogen and progesterone receptors are assessed by immunohistochemistry, HER2 by immunohistochemistry with in situ hybridization when indicated, and actionable EGFR alterations by molecular testing. These tissue biomarkers may be predictive, prognostic, or both, depending on the tumor type.^3,4

Enzyme markers include lactate dehydrogenase, which is prognostic in hematologic malignancy but rises nonspecifically in many cancers, and alkaline phosphatase, which can indicate bone or hepatic involvement in metastatic disease. PSA is also an enzyme measured by immunoassay.¹

Immunoassay behavior behind tumor-marker results

Tumor-marker assays share several sandwich-immunoassay failure modes, and assay errors can alter treatment decisions.¹

The hook effect. Tumor-marker concentrations can span many orders of magnitude; hCG runs from about 10 to 10,000,000 mIU/mL. In a sandwich immunoassay, extreme antigen excess saturates the capture and label antibodies separately, prevents sandwich formation, and paradoxically lowers the signal, producing a falsely low result. A specimen with high clinical suspicion but an unexpectedly modest result should be diluted and retested; a true hook-effect specimen shows a higher, more accurate result on dilution.¹

Heterophile antibodies. Circulating antibodies against animal immunoglobulin, including human anti-mouse antibodies from prior mouse-monoclonal-antibody therapy or animal exposure, can cross-link the capture and label antibodies without any analyte present, causing false-positive or, less often, false-negative results. Suspected interference is investigated with dilution studies, blocking reagents, and testing on an alternative platform; no single negative study excludes antibody interference.¹

Standardization. Different manufacturers’ assays for the same marker frequently disagree numerically because antibody specificity, analyte heterogeneity, and reference materials differ. A patient’s serial results must therefore be tracked on one assay platform.¹

Icterus, lipemia, hemolysis, antibody cross-reactivity, and inter-patient carryover can interfere with tumor-marker immunoassays, as they can with other immunoassays.¹

Myocardial injury and infarction

Acute coronary syndrome spans unstable angina without myocyte necrosis through acute myocardial infarction. In suspected acute coronary syndrome, current guidance requires cardiac troponin measurement as soon as possible, preferably with a high-sensitivity assay, and serial testing when the initial result is nondiagnostic.⁵

The Fourth Universal Definition of Myocardial Infarction separates myocardial injury from myocardial infarction. Injury is present when at least one cardiac troponin value exceeds the 99th-percentile upper reference limit, and the injury is acute when serial values rise and/or fall. The term infarction applies only when acute injury is accompanied by at least one of: ischemic symptoms, new pathologic Q waves, new ischemic ST-segment changes, imaging evidence of new regional wall-motion abnormality or loss of viable myocardium, or angiographic or autopsy evidence of atherothrombosis.⁶

ST-segment-elevation myocardial infarction (STEMI) and non-ST-segment-elevation myocardial infarction (NSTEMI) describe electrocardiographic presentations and can occur within different infarction types.⁶

From enzymes to troponin

AST and LD entered clinical use as the first cardiac markers in 1954, but both rise in many noncardiac conditions. Total CK exceeds its reference range 6 to 8 hours after acute myocardial infarction, peaks by 24 hours, and normalizes in 3 to 4 days. A CK more than twice the upper limit of normal historically correlated with infarction. CK-MB became the standard enzymatic marker for decades because of its relative cardiac specificity and rapid rise. It accounts for about 10% to 20% of myocardial CK activity but less than 3% of skeletal-muscle CK activity. Chronic muscle disease, end-stage renal disease, and extreme exercise can raise total CK and CK-MB while troponin remains normal if the myocardium is undamaged. Sensitive cardiac troponin immunoassays displaced the enzyme panel.¹

Myoglobin has a plasma half-life of about 9 minutes and rises before troponin. Because skeletal muscle releases the same protein, its cardiac specificity is limited and it is used only with a cardiac-specific marker.¹

Cardiac troponin

The troponin complex regulates calcium-dependent actin-myosin interaction in striated muscle: troponin T binds tropomyosin, troponin I inhibits actin-myosin binding, and troponin C binds calcium to reverse that inhibition. Cardiac muscle expresses its own troponin I and troponin T gene products, distinct from the fast- and slow-twitch skeletal isoforms, while slow-twitch skeletal and cardiac muscle share the same troponin C. Monoclonal antibodies against the cardiac-specific epitopes give the assays their specificity, and cTnI remains specific for cardiac injury even in acute or chronic skeletal-muscle disease. cTnI and cTnT are the preferred biomarkers of myocardial necrosis, and an elevated result is defined as a value above the 99th-percentile upper reference limit.^1,6

High-sensitivity assays

High-sensitivity troponin assays use a two-site sandwich immunoassay: a capture antibody binds one troponin epitope, a labeled detection antibody binds a second epitope on the same molecule, and the chemiluminescent, electrochemiluminescent, or fluorescent signal is proportional to concentration. The AACC and IFCC analytical criteria for the high-sensitivity designation require a coefficient of variation of 10% or less at the 99th-percentile upper reference limit and a measurable concentration at or above the assay’s limit of detection in at least half of a healthy reference population. A measurable low-level troponin in a healthy person reflects normal myocyte turnover. Because men have higher baseline troponin than women, current recommendations derive separate 99th-percentile limits by sex, and each manufacturer’s cutoffs apply only to that manufacturer’s assay. High-sensitivity assays detect lower concentrations earlier than older assays, so current rule-in and rule-out pathways repeat a nondiagnostic high-sensitivity result at assay-specific intervals of 1 to 2 hours, compared with 3 to 6 hours for a conventional assay.^5,7

Kidney disease

Chronic kidney disease impairs troponin clearance and often causes low-grade chronic myocardial injury, so cTnI and cTnT can remain above the 99th percentile without acute coronary disease. Hemodialysis with a high-flux membrane can lower measured troponin by roughly a quarter to a third, low-flux membranes do not, and cTnT can rise after dialysis in patients with underlying cardiovascular disease, consistent with dialysis-related cardiac strain. The same 99th-percentile threshold applies to dialysis patients, but interpretation must account for chronic baseline elevation and post-dialysis variability.¹

Interferences and serial testing

Heterophile antibodies can interfere with troponin assays. Investigate suspected interference with dilution studies, blocking reagents, and an alternative platform; no single negative study excludes it. Excess biotin from high-dose supplements falsely lowers results in streptavidin-biotin sandwich formats. A clinically discordant result should prompt review of supplement use. Macrotroponin, an immunoglobulin-troponin complex that resists renal clearance, produces a persistent elevation without the expected rise-and-fall pattern. Polyethylene glycol precipitation or testing on a different assay helps identify it. Hemolysis shifts troponin recovery in an assay-specific, unpredictable direction, so a specimen whose hemolysis index exceeds the laboratory’s reporting threshold is redrawn. Antibody pairs, epitope recognition, and calibration differ among manufacturers. cTnI and cTnT results are not interchangeable between assays or platforms, and serial testing to establish a rise and/or fall must use the same assay on the same platform throughout.^1,8

Injury beyond ischemia

Myocyte death ranges from orderly, energy-dependent apoptosis to disordered necrosis as ischemia progresses and ATP supply fails. The same biomarker elevations occur in genetic and stress-related cardiomyopathies, decompensated heart failure and volume overload, myocarditis, cardiotoxic chemotherapy, cardioversion, and chest trauma. These causes do not represent coronary atherothrombosis. The Universal Definition therefore separates myocardial injury from myocardial infarction.^1,6

Natriuretic peptides and heart failure

Atrial natriuretic peptide and B-type natriuretic peptide (BNP) are structurally related hormones that reduce intravascular volume through natriuresis, diuresis, and vasodilation and blunt angiotensin II and norepinephrine signaling. C-type natriuretic peptide acts mainly through local vascular and tissue signaling. Dendroaspis natriuretic peptide is a venom-derived research peptide, not a human cardiac biomarker. Myocardial proBNP is cleaved by corin and furin into biologically active BNP and biologically inert N-terminal pro-B-type natriuretic peptide (NT-proBNP). Routine heart-failure testing uses BNP or NT-proBNP. Increased cardiac pressure, volume load, and hypertrophy raise both markers. They predict morbidity and mortality in heart failure and help distinguish cardiac from noncardiac causes of dyspnea.^1,9

Both peptides are measured by sandwich immunoassay with capture and detection antibodies against distinct epitopes. BNP and NT-proBNP are structurally and immunologically distinct molecules, so each is reported against its own reference interval. Therapeutic recombinant BNP, nesiritide, is detected by BNP immunoassays but not by NT-proBNP assays. An elevated cardiac troponin in heart failure without acute coronary syndrome also carries independent prognostic value, likely reflecting ongoing wall-stress-related myocyte injury, reduced coronary perfusion, and impaired renal troponin clearance.^1,9

Inflammatory and thrombotic cardiovascular markers

High-sensitivity C-reactive protein. Standard CRP assays detect the large increases of acute inflammation, whereas high-sensitivity CRP (hs-CRP) resolves the low concentrations used for cardiovascular risk assessment. In the 2026 ACC/AHA dyslipidemia guideline, hs-CRP of 2 mg/L or more on more than one occasion, without another identified cause, is a risk enhancer for atherosclerotic cardiovascular disease rather than a stand-alone diagnosis or treatment indication.¹⁰

Homocysteine, a sulfur-containing amino acid formed by demethylation of dietary methionine, circulates 80% to 90% protein-bound, with the remainder as free thiol, disulfide, and mixed disulfide forms; total plasma homocysteine sums all of them.¹

Extreme elevation, as in inherited homocystinuria, causes premature atherosclerosis and arterial and venous thromboembolism. More modest elevations are associated with cardiovascular risk, but association does not establish causation. Folate and other B vitamins lower homocysteine, yet randomized homocysteine-lowering trials have not consistently reduced cardiovascular events and do not support broad claims of benefit for ischemic heart disease, deep-vein thrombosis, or stroke.¹

Myeloperoxidase, released by neutrophils recruited to an inflamed vessel wall, is elevated in acute coronary syndrome and chronic coronary disease and adds prognostic information about plaque instability, alongside CRP and troponin, independent of standard clinical risk factors.¹

D-dimer is a fibrin-degradation product composed of two cross-linked D domains from adjacent fibrin monomers and released by plasmin. In a patient with low or intermediate pretest probability of pulmonary embolism, a negative D-dimer has sufficient negative predictive value to exclude the diagnosis. A positive result is nonspecific.¹

References

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3. Allison KH, Hammond MEH, Dowsett M, et al. Estrogen and progesterone receptor testing in breast cancer: ASCO/CAP guideline update. J Clin Oncol. 2020;38(12):1346-1366. doi:10.1200/JCO.19.02309.
4. Wolff AC, Somerfield MR, Dowsett M, et al. Human epidermal growth factor receptor 2 testing in breast cancer: ASCO-College of American Pathologists guideline update. J Clin Oncol. 2023;41(22):3867-3872. doi:10.1200/JCO.22.02864.
5. Rao SV, O'Donoghue ML, Ruel M, et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline for the management of patients with acute coronary syndromes: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2025;151(13):e771-e862. doi:10.1161/CIR.0000000000001309.
6. Thygesen K, Alpert JS, Jaffe AS, et al. Fourth universal definition of myocardial infarction (2018). Circulation. 2018;138(20):e618-e651. doi:10.1161/CIR.0000000000000617.
7. Wu AHB, Christenson RH, Greene DN, et al. Clinical laboratory practice recommendations for the use of cardiac troponin in acute coronary syndrome: expert opinion from the Academy of the American Association for Clinical Chemistry and the Task Force on Clinical Applications of Cardiac Bio-Markers of the International Federation of Clinical Chemistry and Laboratory Medicine. Clin Chem. 2018;64(4):645-655. doi:10.1373/clinchem.2017.277186.
8. US Food and Drug Administration. The FDA warns that biotin may interfere with lab tests: FDA safety communication. Updated November 5, 2019. Accessed August 30, 2026.
9. Heidenreich PA, Bozkurt B, Aguilar D, et al. 2022 AHA/ACC/HFSA guideline for the management of heart failure: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2022;145(18):e895-e1032. doi:10.1161/CIR.0000000000001063.
10. Blumenthal RS, Morris PB, Gaudino M, et al. 2026 ACC/AHA/AACVPR/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA guideline on the management of dyslipidemia: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. Circulation. 2026;153:e1154-e1276. doi:10.1161/CIR.0000000000001423.