Cancer Biomarker Testing Guide: CEA, CA-125, PSA, CTC — What Patients Need to Know (2026)

By Editorial Team June 01, 2026

By The Medical Advisor Editorial Team | Updated June 2026 | Reviewed for accuracy against current clinical guidelines

Executive Summary

Cancer biomarkers are measurable substances — proteins, hormones, genetic fragments, or even whole cells — that signal the possible presence, progression, or recurrence of cancer. They are detected through blood tests, urine, tissue, or other body fluids.

This guide covers the four most clinically relevant biomarkers patients encounter:

CEA (Carcinoembryonic Antigen) — primarily colorectal, lung, and breast cancer
CA-125 — primarily ovarian cancer
PSA (Prostate-Specific Antigen) — prostate cancer screening and monitoring
CTC (Circulating Tumour Cells) — a newer "liquid biopsy" approach applicable across cancer types

Understanding what these tests can — and cannot — tell you is essential for making informed decisions alongside your oncologist.

Important disclaimer: Biomarker tests are tools, not diagnoses. Elevated levels require clinical correlation and further investigation. This guide is for educational purposes and does not constitute medical advice.

What Are Cancer Biomarkers?

A cancer biomarker is a biological molecule found in blood, tissues, or other body fluids that is produced either by a tumour or by the body in response to a tumour. The ideal biomarker would be:

Specific — elevated only in the presence of cancer, not benign conditions
Sensitive — detectable even at early disease stages
Prognostic — able to predict disease course
Actionable — its level guides treatment decisions

In practice, no current biomarker perfectly meets all four criteria. Each has known limitations, and results must always be interpreted in clinical context.

Types of biomarkers

Protein biomarkers are the most commonly used in clinical practice — CEA, CA-125, and PSA all fall into this category. They are secreted by tumour cells or surrounding tissue and measured in the blood.

Cellular biomarkers include circulating tumour cells (CTCs), which are intact cancer cells shed from a primary tumour into the bloodstream. CTC testing represents a form of "liquid biopsy."

Genetic/molecular biomarkers include circulating tumour DNA (ctDNA), mutations (e.g. BRCA1/2, KRAS, EGFR), and methylation patterns. These are increasingly used in precision oncology and are beyond the scope of this guide, though they are the future of early detection.

CEA — Carcinoembryonic Antigen

What is CEA?

CEA is a glycoprotein normally produced during foetal development. In healthy adults, blood levels are very low. It was first described in 1965 by Gold and Freedman as a marker of colorectal cancer.

What cancers is CEA used for?

CEA is most commonly elevated in:

Colorectal cancer (most validated use)
Lung cancer (non-small cell)
Breast cancer
Pancreatic cancer
Gastric (stomach) cancer
Thyroid cancer (medullary type)
Ovarian cancer

Normal reference ranges

Population	Normal CEA
Non-smokers	< 2.5 ng/mL
Smokers	< 5.0 ng/mL
Mild elevation (non-specific)	5–10 ng/mL
Suspicious for malignancy	> 10 ng/mL
Advanced/metastatic disease	Often > 20 ng/mL

Note: Reference ranges may vary slightly between laboratories. Always interpret against your lab's own reference interval.

Non-cancerous causes of elevated CEA

CEA is not cancer-specific. It can be elevated in:

Smoking — even moderate smoking raises baseline CEA
Liver disease (cirrhosis, hepatitis)
Inflammatory bowel disease (Crohn's, ulcerative colitis)
Peptic ulcer disease
Pancreatitis
Hypothyroidism
Chronic obstructive pulmonary disease (COPD)
Benign breast disease
Pregnancy

This is why CEA is not recommended as a screening tool for cancer in asymptomatic people — the false-positive rate is high.

How CEA is used clinically

Monitoring treatment response: CEA is most valuable for patients already diagnosed with colorectal cancer. A falling CEA during chemotherapy or after surgery suggests effective treatment. A rising CEA after remission raises concern for recurrence.

Detecting recurrence: After curative resection of colorectal cancer, CEA is monitored every 3–6 months for the first 2 years, then annually. A sustained rise prompts imaging to detect recurrence before it becomes symptomatic.

Staging prognosis: A very high pre-operative CEA (> 5 ng/mL) in colorectal cancer is associated with poorer prognosis and higher likelihood of metastasis.

CEA limitations

It has low sensitivity for early-stage colorectal cancer — approximately 30–40% of Stage I–II patients will have normal CEA despite active tumours
It cannot localise where cancer is — an elevated level requires imaging to find the source
It is not useful for screening in the general population

Integrative considerations

Several natural compounds have been studied for their ability to reduce tumour-derived CEA in the context of adjuvant therapy:

Curcumin — shown in some studies to downregulate CEA expression in colorectal cancer cell lines
Green tea (EGCG) — associated with lower colorectal cancer risk in population studies
Sulforaphane (from broccoli) — epigenetic modulation of cancer cell expression patterns

These are not substitutes for oncological monitoring but may be relevant in an integrative protocol.

CA-125 — Cancer Antigen 125

What is CA-125?

CA-125 (also called MUC16) is a protein found on the surface of many ovarian cancer cells and some normal tissue. It is the most widely used biomarker for epithelial ovarian cancer — the most common and deadliest form of ovarian cancer.

What cancers is CA-125 used for?

CA-125 is elevated in:

Epithelial ovarian cancer (primary use)
Fallopian tube cancer
Primary peritoneal cancer
Endometrial cancer
Cervical adenocarcinoma
Uterine cancer
In men: sometimes elevated in pancreatic and lung cancer

Normal reference ranges

Interpretation	CA-125 Level
Normal (pre-menopausal)	< 35 U/mL
Normal (post-menopausal)	< 35 U/mL (stricter interpretation applies)
Borderline	35–65 U/mL
Elevated — warrants investigation	> 65 U/mL
Highly elevated — strong concern	> 200 U/mL

Post-menopausal women with elevated CA-125 carry a higher risk of malignancy than pre-menopausal women with the same level — the RMI (Risk of Malignancy Index) score takes this into account alongside ultrasound findings.

Non-cancerous causes of elevated CA-125

Like CEA, CA-125 is not specific to cancer:

Endometriosis — can cause very high CA-125 (sometimes > 100 U/mL)
Uterine fibroids
Pelvic inflammatory disease
Peritonitis
Liver disease
Heart failure
Kidney disease
Normal menstruation (CA-125 fluctuates with the cycle)
First trimester pregnancy

This is why CA-125 alone is not sufficient for ovarian cancer screening — particularly in pre-menopausal women.

How CA-125 is used clinically

Diagnosis support: Used alongside transvaginal ultrasound and the HE4 (Human Epididymis Protein 4) marker. The ROMA algorithm (Risk of Ovarian Malignancy Algorithm) combines CA-125 and HE4 with menopausal status to calculate malignancy risk — this outperforms CA-125 alone.

Treatment monitoring: Rising CA-125 during chemotherapy (typically carboplatin + paclitaxel) suggests resistance; falling levels suggest response. A 50% reduction within three cycles is a positive prognostic indicator.

Recurrence detection: After remission, CA-125 is checked every 3 months. The CALYPSO and ICON3 trials showed that rising CA-125 predicts clinical recurrence by 2–5 months on average — but importantly, early treatment triggered by CA-125 alone (versus waiting for symptoms) does not improve overall survival in ovarian cancer. This remains controversial.

The OVA1 and Overa tests are multivariate assays approved by the FDA that combine CA-125 with other serum proteins (transferrin, apolipoprotein A1, transthyretin, beta-2 microglobulin) to improve discrimination between benign and malignant pelvic masses.

CA-125 limitations

Cannot distinguish between ovarian and other pelvic cancers
Falsely elevated in many benign gynaecological conditions
Approximately 20% of epithelial ovarian cancers — particularly the mucinous subtype — are CA-125 negative even at advanced stages
Not validated as a population screening tool (UKCTOCS trial showed CA-125 screening did not reduce ovarian cancer mortality)

The ROCA test

The Risk of Ovarian Cancer Algorithm (ROCA) monitors the rate of change in CA-125 over time rather than using a fixed threshold. It is used in some high-risk surveillance programmes for women with BRCA mutations and has shown better sensitivity than a single threshold measurement.

Integrative considerations

Vitamin D deficiency is associated with higher ovarian cancer incidence and poorer prognosis. Optimising vitamin D (target 25-OH-D > 60 ng/mL) is widely recommended in integrative oncology
IP6 (inositol hexaphosphate) has been studied as an adjunct in ovarian cancer protocols
Berberine — preclinical evidence for PI3K/AKT pathway inhibition relevant to ovarian cancer; see the companion article on PI3K/mTOR

PSA — Prostate-Specific Antigen

What is PSA?

PSA is a serine protease enzyme produced almost exclusively by the prostate gland — both healthy and malignant prostate tissue produces it. It is the most widely used cancer biomarker in the world and one of the most controversial.

Normal PSA ranges (by age)

Age-specific ranges are preferred over a universal cut-off:

Age Group	Suggested Upper Normal
40–49 years	2.5 ng/mL
50–59 years	3.5 ng/mL
60–69 years	4.5 ng/mL
70–79 years	6.5 ng/mL

Most labs use a universal cut-off of 4.0 ng/mL, but this misses cancers in younger men (who should have lower levels) and over-triggers biopsy in older men.

PSA density and PSA velocity

PSA density = PSA level ÷ prostate volume (measured by ultrasound). A density > 0.15 ng/mL/cc increases suspicion for cancer versus benign prostatic hyperplasia (BPH).

PSA velocity = the rate of PSA rise over time. An annual rise > 0.75 ng/mL/year (if PSA > 4) or > 0.35 ng/mL/year (if PSA < 4) raises concern for cancer, though this remains debated.

PSA doubling time (PSADT) — used in active surveillance. A doubling time < 3 years suggests aggressive disease requiring intervention.

Free vs. total PSA

PSA circulates in two forms:

Bound PSA — attached to proteins; associated with cancer
Free PSA — unbound; higher proportions are more common in BPH

% free PSA = (free PSA ÷ total PSA) × 100

A free PSA percentage < 10% significantly increases the probability of cancer (approximately 56% probability). > 25% free PSA suggests BPH. This test helps reduce unnecessary biopsies when total PSA is in the 4–10 ng/mL "grey zone."

Non-cancerous causes of elevated PSA

Benign prostatic hyperplasia (BPH) — the most common cause of elevated PSA
Prostatitis (infection/inflammation) — can cause dramatic temporary rises
Recent ejaculation (within 24–48 hours)
Vigorous cycling or perineal trauma
Recent prostate biopsy or TURP (can elevate PSA for weeks)
Urinary tract infection
Certain medications (testosterone, finasteride artificially lowers PSA — the PSA should be doubled for interpretation in men on finasteride)

The PSA screening controversy

The two landmark PSA screening trials tell different stories:

PLCO trial (US) — found no survival benefit from PSA screening versus usual care. However, this trial was heavily criticised for contamination (many control patients received PSA testing anyway).

ERSPC trial (European) — found a 21% reduction in prostate cancer death with PSA screening, but at the cost of significant overdiagnosis and overtreatment of low-grade, clinically insignificant cancers.

The current consensus from major guidelines:

Shared decision-making is recommended — men aged 55–69 should discuss pros and cons with their doctor
Screening before age 40 is not recommended
High-risk men (Black/African descent, family history of prostate/breast/ovarian cancer, known BRCA2 mutation) benefit most from earlier and more frequent screening

The 4Kscore and Prostate Health Index (PHI)

These validated multimarker tests outperform PSA alone:

4Kscore combines total PSA, free PSA, intact PSA, and human kallikrein 2 (hK2) with age, DRE result, and prior biopsy status to calculate the probability of high-grade (Gleason ≥ 7) prostate cancer. This markedly reduces unnecessary biopsies.

PHI (Prostate Health Index) = ([-2]proPSA / free PSA) × √total PSA. An elevated PHI (> 55) is associated with higher risk of aggressive cancer. FDA-approved; available in many countries including Malaysia.

Active surveillance and PSA

For men with low-risk prostate cancer, active surveillance (AS) avoids immediate treatment while monitoring progression. PSA monitoring is the cornerstone of AS, with regular biopsies and increasingly, multiparametric MRI (mpMRI). A rising PSA on AS is not an automatic trigger to treat — the rate of rise (doubling time) and confirmatory biopsy matter.

Integrative considerations for PSA management

A range of lifestyle and supplement interventions have evidence for supporting prostate health or slowing PSA progression in early disease:

Lycopene (tomatoes, especially cooked) — associated with lower PSA and reduced prostate cancer risk in multiple studies. Dose typically 10–30 mg/day
Pomegranate extract — shown in a phase II trial to extend PSA doubling time in men with recurrent prostate cancer after surgery/radiation
Green tea catechins — a randomised trial (Bettuzzi et al.) showed that EGCG supplementation significantly reduced progression from high-grade PIN to prostate cancer
Modified citrus pectin — preliminary evidence for slowing PSA velocity
Selenium — mixed evidence; the SELECT trial showed no benefit from supplementation in unselected men, but selenium status at baseline matters
Curcumin — androgen receptor modulation; synergy with androgen deprivation therapy being studied
Diet: A whole-food plant-rich diet low in saturated animal fat is consistently associated with slower prostate cancer progression. The MEAL (Men's Eating and Living) trial showed significant slowing of PSA rise in men adopting a plant-based diet

CTC — Circulating Tumour Cells

What are CTCs?

Circulating tumour cells are intact cancer cells that detach from a primary tumour (or metastasis) and travel through the bloodstream. Detecting even a few of these rare cells provides a "liquid biopsy" — a non-invasive window into tumour biology.

CTCs were first described in 1869 by Thomas Ashworth, who observed cells resembling cancer cells in the blood of a man who had died from cancer. Reliable clinical assays only became available in the 2000s.

How CTC testing works

CellSearch system (Menarini/Veridex) — the only FDA-cleared CTC platform for clinical use. It uses immunomagnetic enrichment to isolate cells expressing the epithelial marker EpCAM, then counts cells expressing cytokeratins 8, 18, and 19 while being negative for the white blood cell marker CD45.

Blood volume tested: typically 7.5 mL.

Newer platforms use microfluidic chips, size-based filtration, or functional assays to capture CTCs regardless of EpCAM expression — important because aggressive, epithelial-to-mesenchymal transition (EMT) cancer cells downregulate EpCAM and are missed by CellSearch.

CTC reference thresholds (CellSearch)

Cancer Type	Unfavourable Count
Metastatic breast cancer	≥ 5 CTCs per 7.5 mL blood
Metastatic colorectal cancer	≥ 3 CTCs per 7.5 mL blood
Metastatic prostate cancer	≥ 5 CTCs per 7.5 mL blood

In healthy individuals, CTCs should be undetectable (0 per 7.5 mL).

What CTC counts tell us

Prognosis: In metastatic breast, colorectal, and prostate cancer, CTC count is one of the strongest independent prognostic factors. Patients with ≥ 5 CTCs (breast, prostate) have significantly shorter progression-free and overall survival than those with < 5.

Treatment monitoring: Converting from an unfavourable to a favourable CTC count (e.g. ≥ 5 dropping to < 5) within the first cycle of a new treatment predicts improved survival — sometimes weeks before imaging shows a response. This is particularly valuable in metastatic breast and prostate cancer.

Early recurrence detection: Rising CTCs after remission may signal recurrence before imaging or symptoms. Research is ongoing; this is not yet standard practice.

Treatment resistance: Molecular analysis of captured CTCs can identify resistance mutations (e.g. androgen receptor splice variant 7 / AR-V7 in castration-resistant prostate cancer — men with AR-V7-positive CTCs respond poorly to enzalutamide and abiraterone but may respond to taxane chemotherapy).

CTC limitations

Currently validated only for metastatic cancers — not useful for early-stage screening in most settings
EpCAM-based platforms miss EMT-type cells that may represent the most dangerous, stem-like cancer cell population
Rare cell counts mean results can be variable between draws
Not yet standard of care in most oncology guidelines outside of research centres
High cost and limited availability, particularly in Southeast Asia

The RGCC test

The RGCC (Research Genetic Cancer Centre) offers a broader liquid biopsy panel (Oncocount, Onctrace, Oncotrace+) that combines CTC enumeration with molecular profiling, testing CTCs against a panel of chemotherapy drugs and natural compounds to guide treatment selection. While not FDA-approved and limited by regulatory-grade clinical validation, it is used in integrative oncology settings including some Malaysian and Singapore clinics. Patients should understand the evidence base before pursuing this test.

Circulating tumour DNA (ctDNA) — the next frontier

While not CTCs, ctDNA deserves mention. ctDNA consists of fragments of tumour-derived DNA shed into the bloodstream. Tests like Guardant360, FoundationOne Liquid CDx, and GRAIL's Galleri multi-cancer early detection (MCED) test analyse ctDNA for cancer-associated mutations and methylation patterns.

The Galleri test (GRAIL) screens for 50+ cancer types from a single blood draw with a reported overall cancer signal sensitivity of approximately 67% and 99.5% specificity — with much higher sensitivity for late-stage cancers. As of 2026, it is available commercially in the US and is under evaluation by NHS England in the SYMPLIFY trial.

Comparing the Four Biomarkers: A Quick Reference

Feature	CEA	CA-125	PSA	CTC
Primary cancer	Colorectal	Ovarian	Prostate	Multiple (metastatic)
FDA-approved screening?	No	No	Conditional	No (monitoring only)
Screening utility	Low	Low	Controversial	Research stage
Monitoring utility	High	High	High	High (metastatic)
Recurrence detection	Yes	Yes	Yes	Emerging
Non-cancer elevation	Common	Common	Common	Rare
Actionable results	Yes (colorectal)	Yes (ovarian)	Yes (prostate)	Yes (metastatic)

Understanding Your Results: A Patient's Checklist

If your doctor has ordered one of these tests, here are the most important questions to ask:

1. Why is this test being ordered? Is it for screening, diagnosis, treatment monitoring, or recurrence surveillance? The clinical context completely changes how to interpret the result.

2. What is the trend, not just the number? A single result rarely tells the full story. A CEA of 8 that was previously 3 is more concerning than a stable CEA of 8 that has been unchanged for two years.

3. What other tests are needed alongside this result? An elevated CA-125 alone is insufficient — it must be combined with ultrasound and clinical history. An elevated PSA requires free PSA, ideally PHI or 4Kscore, and possibly mpMRI before biopsy.

4. Have benign causes been excluded? Before pursuing invasive investigations, ensure that common non-cancerous causes (infection, inflammation, smoking, menstruation) have been considered.

5. Is this result changing my management? Biomarker testing should drive decisions. If your oncologist is monitoring CEA after colorectal cancer surgery, agree in advance what threshold or trend will trigger the next step.

The Future of Biomarker Testing

The field is moving rapidly toward multimarker panels and AI-assisted interpretation:

Multi-cancer early detection (MCED) tests like Galleri aim to replace single-marker screening with a pan-cancer liquid biopsy
Methylation-based tests can identify the tissue of origin of ctDNA, pointing to where a cancer is located even before imaging
Proteomics panels combine dozens of proteins simultaneously; EarlyCDT (Oncimmune) uses autoantibody panels for lung cancer early detection
Tumour microenvironment biomarkers — PD-L1 expression, tumour mutational burden (TMB), microsatellite instability (MSI) — are used to predict immunotherapy response

Precision oncology is shifting away from "one marker, one cancer" toward integrated molecular portraits of individual tumours.

Key Takeaways

No single biomarker is diagnostic of cancer on its own. All require clinical correlation, imaging, and often tissue biopsy.
CEA is most useful for monitoring colorectal cancer — not screening. Smokers have higher baseline levels.
CA-125 is best used alongside HE4 and ultrasound in peri- and post-menopausal women. Pre-menopausal elevation is common in benign conditions.
PSA screening remains valuable but requires nuanced interpretation. Free PSA, PHI, or 4Kscore reduce unnecessary biopsies. Men on finasteride must double their PSA for correct interpretation.
CTC testing is validated for monitoring metastatic breast, colorectal, and prostate cancer. It is not a screening tool but provides real-time prognostic information.
Trends matter more than single values. Consistent rising trends are more clinically meaningful than single elevated readings.
Integrative approaches (lycopene, EGCG, curcumin, vitamin D) may complement conventional monitoring but do not replace it.

References and Further Reading:

Duffy MJ. Tumour markers in clinical practice: a review focusing on common solid cancers. Medical Oncology. 2021.
Diamandis EP. CEA, CA-125, PSA: biomarkers in clinical practice. Critical Reviews in Clinical Laboratory Sciences. 2019.
Bast RC Jr et al. The biology of ovarian cancer: new opportunities for translation. Nature Reviews Cancer. 2009.
Loeb S, Catalona WJ. The prostate health index: a new test for the detection of prostate cancer. Therapeutic Advances in Urology. 2014.
Cristofanilli M et al. Circulating tumour cells, disease progression, and survival in metastatic breast cancer. New England Journal of Medicine. 2004.
Klein EA et al. Clinical validation of a targeted methylation-based multi-cancer early detection test using an independent validation set. Annals of Oncology. 2021.
Cooperberg MR, Carroll PR. Trends in management for patients with localized prostate cancer, 1990-2013. JAMA. 2015.

Genetics, Genomics and Precision Oncology (2026): The Ultimate Guide to Precision Oncology, Targeted Therapy, and the Future of Cancer Treatment.

This article is for educational purposes only. It does not constitute medical advice. Always discuss biomarker testing decisions with a qualified oncologist or physician. If you are in Malaysia or Singapore, the Find a Doctor section can help you locate an integrative oncology specialist.