How Cancer Is Diagnosed

Step 1 — Finding the abnormality

Ultrasound, X-ray, CT, MRI or mammography identify a lesion and describe its size and features. Imaging can be strongly suggestive, but it cannot confirm cancer on its own. Tumour markers such as CA-125, PSA or CEA are useful for monitoring treatment, and are unreliable as standalone diagnostic tests.

Step 2 — Biopsy and pathology

A biopsy takes a tissue sample for examination under a microscope. This is the step that confirms cancer and identifies its type and grade. Immunohistochemistry adds further detail — hormone receptor and HER2 status in breast cancer, or the lymphoma subtype — which directly determines the drugs used.

Step 3 — Staging

Staging establishes how far the cancer has spread, using PET-CT, CT, MRI or a bone scan depending on the cancer type. For blood cancers, bone marrow aspiration and biopsy replaces conventional staging. Stage is what separates a curative plan from a control-focused one, so it must be complete before treatment starts.

Step 4 — Molecular and biomarker testing

Modern oncology often needs one more layer: EGFR, ALK and PD-L1 in lung cancer, HER2 in breast and stomach cancer, RAS and MSI in colorectal cancer, cytogenetics and molecular markers in leukaemia. These tests decide whether a targeted tablet or immunotherapy is possible instead of, or alongside, chemotherapy.

Questions worth asking your oncologist

• What exactly is the diagnosis, in the words of the pathology report?
• What is the stage, and is staging complete?
• Have all relevant molecular tests been done?
• Is the intent of treatment cure, control or symptom relief?
• What are the alternatives, and what happens if we wait?

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