How Cancer Is Diagnosed: Tests, Biopsy and Tumour Markers

Cancer is diagnosed in layers. Blood tests and imaging raise or lower the suspicion, and a contrast-enhanced CT or PET-CT shows where the disease is. But the diagnosis is confirmed only on tissue: a biopsy examined under the microscope, with immunohistochemistry to type the cancer. Tumour markers support the picture and track treatment, but they are not specific enough to diagnose cancer alone.

Dr. Nithin S.G, Consultant, Medical Oncology, Fortis Flt. Lt. Rajan Dhall Hospital, Vasant Kunj, New Delhi, India, gave referring doctors a practical sequence for the work-up, and a set of rules about what not to do. Several avoidable mistakes in cancer care happen here, before an oncologist is involved: an aspiration where a biopsy was needed, a biopsy of an organ that should go straight to surgery, or a PET scan read as a diagnosis. This article covers each test in turn. The symptoms that should start the work-up are in the warning signs of cancer by type, and the full pathway is in the complete guide to cancer care.

First-line blood tests for suspected cancer

When a patient has a symptom that could be cancer, the first step after examination is a set of routine blood tests:

• Complete blood count. Most patients with cancer have some degree of anaemia, the anaemia of chronic disease, often compounded by blood loss or by cancer in the bone marrow. In blood cancers the platelet count may be low, and the white cell count may be either high or low.
• Liver function tests. When cancer has spread to the liver (stage IV disease), the patient may develop jaundice or raised liver enzymes.
• Kidney function tests. These are needed to plan treatment whatever the cancer, not only in kidney cancer. They can also be abnormal in leukaemia, where the breakdown of large numbers of leukaemic cells raises the creatinine.
• Serum LDH (lactate dehydrogenase). An enzyme released when cells turn over rapidly. It is frequently raised in lymphoma, and should be tested whenever lymphoma is suspected because lymph nodes are enlarged.

None of these tests diagnoses cancer. They establish the patient's baseline, point towards certain cancers, and show whether organs that treatment depends on are working.

Choosing the right scan: ultrasound, CT or MRI

Imaging follows the symptom.

• Breast lump: mammography.
• Abdominal pain or discomfort, weight loss, blood in the stool, urinary symptoms: ultrasound.
• Most suspected cancers, including lung and abdominal cancers: a CT scan, and always a contrast-enhanced CT. Dr. Nithin's rule was absolute: never order a plain CT for a suspected cancer.

Triple-phase CT for liver cancer

If an ultrasound shows one or more small lesions in the liver and the liver function tests are deranged, the next test is a triple-phase CT: a contrast CT that images the liver at three timed points after injection. It is the scan that helps make the diagnosis of primary liver cancer.

When MRI is the right test

In most cancers a CT scan is enough. MRI is indicated in specific situations:

• Suspected brain tumour: severe headache, visual difficulty and vomiting.
• Suspected uterine cancer: postmenopausal bleeding.
• Rectal, urinary bladder and prostate cancer.
• Cancer of the tongue or mouth, where an MRI is needed before surgery is planned.

Mammography, ultrasound or MRI for breast cancer?

Asked whether mammography or MRI is better for diagnosing breast cancer, Dr. Nithin said the choice depends on the patient's age and on practicality. Mammography is a form of X-ray, and in young women, particularly those under 30 to 35, it is poor at identifying a breast lump. For them, an ultrasound of the breast comes first, and if that is inconclusive, MRI is the next investigation. From about 35 to 40 years of age, mammography becomes effective, and it is the test advised for older women.

The age effect has a known cause. Younger women have denser breast tissue, with more glandular and fibrous tissue, which can hide a tumour on a mammogram; with age, more of the breast is replaced by fat and mammography becomes more sensitive.

MRI is the more sensitive test and, in Dr. Nithin's words, definitely better than mammography, but it costs more and is more demanding for the patient. Mammography is quick and easy, which is why it is usually advised first. For staging a confirmed breast cancer that is locally advanced or causing symptoms, a whole-body PET-CT or a CT of the chest, abdomen and pelvis is preferred; early-stage disease without symptoms does not need whole-body scans.

PET-CT: highly sensitive, not specific

In Dr. Nithin's practice, PET-CT is now done for almost every cancer patient. The most common form is the FDG PET-CT, a whole-body scan using a radioactive glucose tracer that collects in metabolically active tissue. It does two jobs at once: it shows where the cancer is, and it stages the cancer by showing whether it has spread beyond its site of origin.

Its weakness is specificity. Areas of high uptake show as red on the scan, and cancer is not the only thing that lights up. Infections, including tuberculosis, show the same uptake. A positive PET-CT therefore does not mean a patient has cancer. Dr. Nithin's guidance was to make the diagnosis only when the scan, the symptoms and the examination all fit together, never on the PET scan alone.

Two specialised PET scans are much more specific:

• Gallium-68 PSMA PET-CT for prostate cancer. Prostate cancer cells carry a protein called PSMA (prostate-specific membrane antigen) on their surface, and the tracer binds to it.
• Gallium-68 DOTA PET-CT for neuroendocrine tumours, which carry receptors the tracer binds to.

Histopathology: how cancer is diagnosed on tissue

The most important test in cancer diagnosis is histopathology: a biopsy, examined under the microscope. Everything else supports it.

Biopsy vs FNAC: why FNAC is now obsolete

Fine-needle aspiration cytology (FNAC) was once the standard first test for a suspected cancer. Dr. Nithin described it as obsolete today. In FNAC, a fine needle is pushed into the lump and the contents are drawn up with a syringe. What comes out is mostly fluid or blood, with a few tumour cells that have broken away. These are smeared on a slide and examined. If abnormal cells are seen, the pathologist can say that the sample is suggestive of cancer, but not what type of cancer it is.

That is no longer enough. Two decades ago, a cancer in the breast was simply breast cancer. Today breast cancer is divided into several types on histopathology, and treatment depends on the hormone receptor and HER2 status, which must be tested on tissue. The type of most cancers is now decided by immunohistochemistry (IHC), a panel of stains applied to tissue sections, and many treatments depend on genetic tests run on the same tissue. FNAC yields too few cells for most of this, although it remains the standard first test for some sites, such as thyroid nodules.

In a core biopsy, a biopsy gun is pushed into the tumour and fired. A hollow chamber in the needle captures a cylinder of tumour, typically up to about 1 cm long. That core is enough for the pathologist to make the diagnosis and run the stains and tests treatment requires. Whenever cancer is suspected, Dr. Nithin's rule was to go for a biopsy, not FNAC.

How the biopsy is taken

• A lump in the breast, a lymph node, or any palpable lump: biopsy directly.
• A lesion in the abdomen or lung: ultrasound-guided or CT-guided biopsy.
• Oesophageal and stomach cancer: biopsy at upper gastrointestinal endoscopy.
• Colon cancer: biopsy at colonoscopy.

Lymph nodes: take the whole node

When the target is a lymph node in the neck, armpit or another accessible site, Dr. Nithin's instruction was to do an excisional biopsy, removing the whole node, rather than taking a core from it. Lymphoma, the cancer that arises in lymph nodes, is diagnosed partly from the architecture of the intact node, and a broken or fragmented node can make the diagnosis impossible. Where the node is deep in the abdomen or chest and cannot be removed whole, a core biopsy under ultrasound or CT guidance is the alternative.

Breast: core biopsy or excision?

For a suspected breast cancer, a core biopsy is sufficient and there is no need for an excisional biopsy. For a small lump that looks benign, such as a fibroadenoma, excision is an option, but core biopsy is equally effective, and if it confirms a benign tumour, surgery can be avoided altogether.

Receptor testing in breast cancer

The diagnostic procedure for breast cancer does not change with the subtype. Mammography is used for initial evaluation, and the biopsy confirms the diagnosis. IHC on the biopsy then tests for the oestrogen receptor (ER), the progesterone receptor (PR) and HER2. Breast cancer falls into three broad types: hormone receptor positive, HER2 positive and triple negative, where all three tests are negative. Triple-negative breast cancer is more aggressive and is very difficult to treat once it reaches stage IV. How each type is treated is covered in precision oncology and targeted therapy.

Cancers that need no biopsy

Two cancers can be diagnosed without tissue:

• Liver cancer (hepatocellular carcinoma). If a triple-phase CT or MRI shows a lesion with the typical pattern in a liver that is already cirrhotic or chronically infected with hepatitis B, no biopsy is needed. A raised alpha-fetoprotein (AFP), a tumour marker, adds support but is not required.
• Retinoblastoma. This cancer of the eye in children is diagnosed by eye examination alone.

Cancers that should not be biopsied

Dr. Nithin advised against biopsy in some cancers, because breaching the capsule of the organ can spread the cancer. He named three encapsulated organs:

• Kidney. If CT or ultrasound shows a mass in the kidney, go directly to surgery, removing the whole kidney or part of it, which both confirms the diagnosis and treats the patient. (See the nephrectomy cost page.) Current urology guidelines do use kidney mass biopsy selectively, for example when imaging is inconclusive or before ablation or drug treatment.
• Testis. A testicular swelling should never be biopsied.
• Ovary. With an ovarian mass on CT and a raised CA-125, the better course is to proceed directly to surgery.

The testicular swelling

Any man with a swelling in the scrotum should have an ultrasound, which will show whether there is a testicular mass or enlargement. No test confirms the diagnosis before surgery: confirmation comes from removing the testis (a radical orchiectomy) and examining it.

Discussing a case in which orchiectomy for a suspected cancer revealed testicular tuberculosis instead, Dr. Nithin accepted that this can happen but said it is the exception. Most scrotal swellings are benign, but about 80 to 90% of solid masses within the testis on ultrasound are cancer, with tuberculosis and other benign lesions the minority. For that majority, going directly to orchiectomy is the right course, because biopsying a testicular cancer can spread it. His recommendation stands whether or not the tumour markers are raised.

Markers do help. Germ cell tumours of the testis often raise alpha-fetoprotein (AFP), beta-hCG or both: AFP points to a non-seminomatous tumour such as a yolk sac tumour, while pure seminomas do not raise AFP. A raised marker alongside a testicular mass on ultrasound is highly suggestive of cancer.

Tumour markers: what they can and cannot tell you

Tumour markers are proteins produced by some cancers and released into the blood, where they can be measured. Common examples are CA-125 for ovarian cancer, CEA (carcinoembryonic antigen) for colon cancer, and beta-hCG and AFP for testicular cancer.

They are used in three ways:

1. To support a diagnosis when suspicion is already high. An ovarian mass with a raised CA-125, or a testicular mass with a raised beta-hCG, is highly likely to be cancer, and the patient can go directly to surgery.
2. To track response. If a marker was high at diagnosis and falls to normal after surgery or chemotherapy, the disease is responding.
3. To watch for recurrence. After treatment ends, the marker is repeated every three to six months during follow-up to detect a return of the cancer.

The limits of tumour markers

Tumour markers are not specific for cancer. CA-125 can be raised by peritonitis, other abdominal infections and ovarian torsion. CEA can be raised in heavy smokers and in diarrhoeal or colonic infections. A raised marker means something only when the symptoms, the examination and the scans already point to cancer.

PSA and prostate cancer

PSA (prostate-specific antigen) illustrates the problem. Dr. Nithin was direct: PSA is not specific for prostate cancer, and no tumour marker is specific for any single cancer. A raised PSA in a man with an enlarged prostate can come from benign prostatic hyperplasia (BPH) or from cancer. PSA also rises after a digital rectal examination or after ejaculation.

Very high values, such as above 100, are much more suggestive of cancer. If the PSA is that high and the biopsy shows only BPH, the biopsy may simply have missed the cancer, which happens when the needle cores miss the cancerous tissue. In such cases an MRI of the prostate, or a Gallium-68 PSMA PET-CT, can show whether cancer is present and guide a repeat biopsy. If it is consistent with BPH, treat the BPH. The prostate biopsy and grading that follow a confirmed suspicion are covered in prostate cancer staging and the Gleason score.

Other samples that find cancer cells

Where a biopsy is difficult, other samples can find cancer cells:

• Urine cytology for bladder cancer: testing the urine for malignant cells.
• Bronchoalveolar lavage for lung cancer: a pulmonologist washes a section of the lung during bronchoscopy and the fluid is tested.
• Pap smear for cervical cancer.
• Liquid biopsy, a newer blood test for tumour cells and tumour DNA, covered in precision oncology.

How blood cancer is diagnosed

Blood cancers follow their own sequence:

1. Complete blood count. Severe anaemia, a low platelet count (thrombocytopenia), or a white cell count that is too high or too low.
2. Peripheral blood smear. If the count is abnormal, the smear is examined for abnormal immature cells called blasts, which appear in acute leukaemias such as AML and ALL.
3. Serum LDH. Rapidly multiplying cancer cells raise LDH in the blood.
4. Confirmation by flow cytometry and bone marrow aspiration and biopsy.

After the diagnosis: staging

Once cancer is confirmed, scans establish its stage, and stage drives the treatment plan. How staging works, and how surgery, chemotherapy and radiation are sequenced by stage, is covered in the complete guide. Questions from the session on testicular swellings, PSA and biopsy technique are on the Live Discussion page.