Tumor and Cardiac 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.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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. 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. AFP supports treatment and recurrence monitoring.^{1,21 Bishop ML, et al. Clinical Chemistry. 2023.2 Singal AG, et al. AASLD practice guidance on prevention, diagnosis, and treatment… 2023.}

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 cannot diagnose malignancy. In known colorectal cancer, serial results support prognosis and treatment or recurrence monitoring.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

AFP and human chorionic gonadotropin (hCG) together help classify testicular germ-cell tumors:^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

hCG is a 36-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, where concentrations are often very high. A concentration above 100,000 mIU/mL does not by itself indicate trophoblastic disease, because normal first-trimester pregnancy also reaches about that value. Interpret the result with gestational age and serial results. 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 forms an assay detects affect the result.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Hormones serve as markers for the tumors that secrete them: calcitonin for medullary thyroid carcinoma, adrenocorticotropic hormone (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, parathyroid hormone (PTH) for parathyroid adenoma, and prolactin for prolactinoma. Antidiuretic hormone (ADH), or its surrogate copeptin, is used in water-balance evaluation. Inappropriate secretion may be ectopic, classically from small-cell lung cancer. ADH is not a standard marker for posterior-pituitary tumors.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Homovanillic acid (HVA) and vanillylmandelic acid (VMA) are catecholamine metabolites that support the evaluation of neuroblastoma. Current practice commonly uses a random urine specimen with results reported relative to urine creatinine, and a 24-hour collection is required only when the performing laboratory specifies it. Fractionated metanephrines in 24-hour urine or plasma support evaluation for pheochromocytoma and paraganglioma, and chromatography with tandem mass spectrometry has replaced older detection methods for these metabolites. 5-Hydroxyindoleacetic acid (5-HIAA), a serotonin metabolite, supports the diagnosis of carcinoid tumors.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Monoclonal antibodies raised against tumor material defined a family of carbohydrate epitopes, and each marker takes its name from the antibody that defined it.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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 reject a hemolyzed specimen.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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 can raise CA-125 without raising HE4. 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, do not substitute prediction-index values or move the decimal point.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

β₂-Microglobulin is a nonspecific marker of cellular turnover with prognostic value in lymphoproliferative disorders. It also rises with reduced glomerular filtration, so interpret it with renal function.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Tissue receptors are measured on tumor tissue. 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.^{3,43 Allison KH, et al. Estrogen and progesterone receptor testing in breast cancer. 2020.4 Wolff AC, et al. Human epidermal growth factor receptor 2 testing in breast… 2023.}

Enzyme markers include lactate dehydrogenase, which is prognostic in hematologic malignancy and 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.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Tumor-marker assays share several sandwich-immunoassay failure modes, and assay errors can alter treatment decisions.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

The hook effect. Tumor-marker concentrations can span many orders of magnitude. For example, hCG ranges 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. When a result is unexpectedly modest for the clinical suspicion, dilute and retest the specimen. A specimen with a true hook effect gives a higher, more accurate result on dilution.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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. Investigate suspected interference with dilution studies, blocking reagents, and testing on an alternative platform. No single negative study excludes antibody interference.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Standardization. Different manufacturers' assays for the same marker frequently disagree numerically because antibody specificity, analyte heterogeneity, and reference materials differ. Track a patient's serial results on one assay platform.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Icterus, lipemia, hemolysis, antibody cross-reactivity, and inter-patient carryover can interfere with tumor-marker immunoassays, as they can with other immunoassays.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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.^{55 Rao SV, et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline for the management of… 2025.}

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.^{66 Thygesen K, et al. Fourth universal definition of myocardial infarction (2018). 2018.}

ST-segment-elevation myocardial infarction (STEMI) and non-ST-segment-elevation myocardial infarction (NSTEMI) describe electrocardiographic presentations and can occur within different infarction types.^{66 Thygesen K, et al. Fourth universal definition of myocardial infarction (2018). 2018.}

Aspartate aminotransferase (AST) and lactate dehydrogenase (LD) entered clinical use as the first cardiac markers in 1954. Both rise in many noncardiac conditions. Total creatine kinase (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 reference limit 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 and 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 without myocardial injury. Troponin is far more cardiac-specific, although end-stage renal disease, strenuous exercise, and active chronic muscle disease can also raise it, as the troponin sections below explain. Sensitive cardiac troponin immunoassays replaced the enzyme panel.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Myoglobin is cleared rapidly by the kidney and rises before troponin, which was the basis of its former use as an early marker. Because skeletal muscle releases the same protein, its cardiac specificity is poor, so current practice uses a cardiac-specific troponin and no longer uses myoglobin.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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. Slow-twitch skeletal and cardiac muscle share the same troponin C. Monoclonal antibodies against the cardiac-specific epitopes give the assays their specificity. Despite high assay specificity, active chronic skeletal-muscle disease can raise cardiac troponin, more often cardiac troponin T (cTnT) than cardiac troponin I (cTnI), without cardiac injury, so investigate a result that disagrees with the clinical picture before accepting it as cardiac. 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.^{1,61 Bishop ML, et al. Clinical Chemistry. 2023.6 Thygesen K, et al. Fourth universal definition of myocardial infarction (2018). 2018.}

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 American Association for Clinical Chemistry and International Federation of Clinical Chemistry and Laboratory Medicine 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.^{5,75 Rao SV, et al. 2025 ACC/AHA/ACEP/NAEMSP/SCAI guideline for the management of… 2025.7 Wu AHB, et al. Clinical laboratory practice recommendations for the use of… 2018.}

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, and interpretation accounts for chronic baseline elevation and post-dialysis variability.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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. When a result is clinically discordant, review 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 redraw a specimen whose hemolysis index exceeds the laboratory's reporting threshold. 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.^{1,81 Bishop ML, et al. Clinical Chemistry. 2023.8 US Food and Drug Administration. The FDA warns that biotin may interfere with lab tests. 2019.}

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.^{1,61 Bishop ML, et al. Clinical Chemistry. 2023.6 Thygesen K, et al. Fourth universal definition of myocardial infarction (2018). 2018.}

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 comes from venom and is used in research. It has no role as 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.^{1,91 Bishop ML, et al. Clinical Chemistry. 2023.9 Heidenreich PA, et al. 2022 AHA/ACC/HFSA guideline for the management of heart failure. 2022.}

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. NT-proBNP assays do not detect it. 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.^{1,91 Bishop ML, et al. Clinical Chemistry. 2023.9 Heidenreich PA, et al. 2022 AHA/ACC/HFSA guideline for the management of heart failure. 2022.}

High-sensitivity C-reactive protein. Standard CRP assays detect the large increases of acute inflammation. High-sensitivity CRP (hs-CRP) measures the low concentrations used for cardiovascular risk assessment. In the 2026 American College of Cardiology/American Heart Association (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. It is not a stand-alone diagnosis or treatment indication.^{1010 Blumenthal RS, et al. 2026 ACC/AHA/AACVPR/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA… 2026.}

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 includes all of them.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

Extreme elevation, as in inherited homocystinuria, causes premature atherosclerosis and arterial and venous thromboembolism. More modest elevations are associated with cardiovascular risk. That 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.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}

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.^{11 Bishop ML, et al. Clinical Chemistry. 2023.}