Cancer Monitoring Blood Tests: Tumour Markers & Follow-Up Testing

What Are Tumour Markers?

Tumour markers are proteins, hormones, or other substances found in the blood (or sometimes in urine or tissue) that may be produced by cancer cells themselves or by the body’s immune system in response to cancer. They are measured through standard blood tests and play an important role in managing cancer care.

It is crucial to understand their limitations from the outset: most tumour markers are not suitable for screening healthy people for cancer. They lack the sensitivity and specificity needed for population-level screening, meaning they can be elevated in non-cancerous conditions (false positives) and normal in some people who do have cancer (false negatives). Their primary value lies in monitoring known cancers during and after treatment.

PSA (Prostate-Specific Antigen)

PSA is a protein produced by both normal and cancerous prostate cells. It is the most widely known tumour marker and the one most frequently requested as a screening test, though its use remains controversial.

• Normal range: generally below 3.0 µg/L for men under 60, with age-adjusted ranges used in practice.
• Elevated in: prostate cancer, but also benign prostatic hyperplasia (BPH), prostatitis, urinary tract infection, and after vigorous exercise or ejaculation.
• UK guidance: the NHS does not offer routine PSA screening. Men over 50 can request a PSA test through the Prostate Cancer Risk Management Programme after a discussion about its limitations.
• Monitoring role: after prostate cancer treatment, PSA is invaluable. A rising PSA after surgery or radiotherapy may indicate disease recurrence.

CEA (Carcinoembryonic Antigen)

CEA is most commonly associated with colorectal cancer, but it can also be elevated in cancers of the lung, breast, pancreas, and stomach.

• Normal range: below 5 µg/L (higher in smokers).
• Limitations: not all colorectal cancers produce CEA, and it can be elevated in non-malignant conditions including inflammatory bowel disease, pancreatitis, liver cirrhosis, and smoking.
• Monitoring role: CEA is primarily used to monitor patients after colorectal cancer surgery. NICE recommends CEA testing every 3–6 months for at least 3 years after curative treatment to detect early recurrence.

CA-125

CA-125 is associated with ovarian cancer and is the most established marker for this disease.

• Normal range: below 35 U/mL.
• Elevated in: ovarian cancer, but also endometriosis, ovarian cysts, pelvic inflammatory disease, liver disease, menstruation, and pregnancy.
• UK guidance: NICE recommends measuring CA-125 as part of the initial assessment in women presenting with symptoms suggestive of ovarian cancer (persistent bloating, feeling full quickly, pelvic pain, urinary frequency). A level of 35 U/mL or above triggers an ultrasound scan.
• Monitoring: after treatment, CA-125 is used to track response and detect relapse.

CA 19-9

CA 19-9 is most commonly associated with pancreatic cancer, though it is also elevated in cancers of the bile duct, stomach, and colon.

• Normal range: below 37 U/mL.
• Limitations: elevated in obstructive jaundice, pancreatitis, and liver cirrhosis. Approximately 5–10% of the population lack the Lewis antigen and cannot produce CA 19-9, meaning the test will always be negative regardless of disease.
• Monitoring: used to assess response to chemotherapy in pancreatic cancer and detect recurrence after surgery.

AFP (Alpha-Fetoprotein)

AFP is associated with hepatocellular carcinoma (liver cancer) and certain germ cell tumours (testicular cancer, ovarian germ cell tumours).

• Normal range: below 10 IU/mL in non-pregnant adults.
• Liver cancer surveillance: NICE recommends 6-monthly AFP and ultrasound in patients with liver cirrhosis to screen for hepatocellular carcinoma.
• Germ cell tumours: AFP, along with beta-HCG and LDH, forms the standard tumour marker panel for testicular cancer staging and monitoring.

HCG (Human Chorionic Gonadotropin)

Beta-HCG is well known as the pregnancy hormone, but it is also a key tumour marker for gestational trophoblastic disease (molar pregnancy, choriocarcinoma) and testicular germ cell tumours.

• Normal range: below 5 IU/L in non-pregnant individuals.
• Monitoring: in gestational trophoblastic disease, serial HCG measurements guide treatment decisions and determine when chemotherapy can stop. In testicular cancer, HCG is monitored alongside AFP and LDH after orchidectomy.

FBC During Chemotherapy

Beyond tumour markers, a full blood count is one of the most frequently performed tests for cancer patients. Chemotherapy suppresses the bone marrow, leading to:

• Neutropenia — low neutrophil count, increasing infection risk. Chemotherapy is often delayed if neutrophils fall below 1.0 × 10⁹/L.
• Anaemia — low haemoglobin causing fatigue and breathlessness. Transfusion or erythropoiesis-stimulating agents may be needed.
• Thrombocytopenia — low platelet count, increasing bleeding risk.

FBC monitoring is typically performed before each chemotherapy cycle, with additional checks mid-cycle if counts are expected to dip (the “nadir”).

When Tumour Markers Are Useful vs Misleading

Tumour markers are most useful when:

• Monitoring a known cancer’s response to treatment (a falling marker suggests treatment is working).
• Detecting recurrence after curative treatment (a rising marker may indicate relapse before symptoms or imaging changes appear).
• Assessing prognosis at diagnosis (high baseline levels may indicate more advanced disease).

Tumour markers are potentially misleading when:

• Used as a screening test in healthy, asymptomatic individuals (high false positive rate causes unnecessary anxiety and invasive investigations).
• A single result is interpreted in isolation rather than as part of a trend.
• Non-cancerous causes of elevation are not considered (e.g., CA-125 during menstruation).

Always discuss tumour marker results with your oncologist or GP, who will interpret them in the context of your full clinical picture.

Getting Tested at Home

Cancer patients undergoing treatment often require frequent blood tests, which can be tiring when combined with hospital appointments. A mobile phlebotomist can take blood samples at your home for tumour markers, FBC, and other routine monitoring tests, with results sent directly to your clinical team. This can reduce hospital visits and make the monitoring process more comfortable. Visit our home blood test page to find out more.