Metastasis

What it means

When cancer cells travel from where they started to a new site and form a new growth there, the new growth is called a metastasis. On a scan, the radiologist sees a spot or several spots with features that fit how a particular cancer typically spreads. Common destinations are the liver, lungs, bones, lymph nodes, and brain. The word on a report is an interpretation of imaging appearance and pattern — it is a strong suggestion, not a tissue diagnosis on its own.

Why it appears on a CT or MRI report

Reports describe number, size, location, and behaviour on contrast. You may see terms like multiple, scattered, suspicious for metastatic disease, indeterminate but felt to represent metastases, or favoured to be metastatic. Specific organs spread to specific places — colon cancer favours the liver and lungs, prostate cancer favours bone, lung cancer can go almost anywhere. The radiologist also compares with any known primary cancer and prior scans. Without a known primary, similar-looking spots are often described as indeterminate and reviewed in a wider workup.

What it usually means

Metastasis on imaging is a description of appearance, not always a diagnosis. This wording is important: many spots labelled suspicious for metastases turn out, on biopsy or careful follow-up, to be benign cysts, blood vessels, scars, focal nodular hyperplasia in the liver, or unrelated incidental findings. Even in someone with a known cancer, new spots can have other explanations. Tissue confirmation — biopsy of the most accessible spot — remains the gold standard before treatment decisions are made. When metastases are confirmed, modern treatment has changed significantly: many cancers with limited spread are treated with intent to control disease for years, and a small subset of cases (oligometastatic disease) can be treated with curative intent. The report alone does not tell the full prognosis. The oncology team weighs the type of cancer, where the spread is, how much there is, the person's overall health, genetic markers, and treatment options.

When to follow up

Talk to your doctor as soon as you can to plan next steps. Tissue biopsy of the most accessible spot is usually the priority before any treatment is started, especially when there is no confirmed primary cancer or when the report uses words like indeterminate or possible. Ask whether a PET-CT, MRI of a specific area, or tumour markers would help. Seek urgent care for sudden severe pain in a new area, new neurological symptoms, breathlessness, unexplained fractures, or rapid weight loss.

A plain-language way to picture it

Think of dandelion seeds carried on the wind. Most land on hard ground and never grow. Occasionally one finds soil, takes root, and produces a new dandelion far from the original. The new plant looks like the old one because it came from it. On a scan, the radiologist is trying to spot a young plant and judge whether it really came from the same parent — sometimes it has, sometimes it just looks similar. Confirming the parent is what the biopsy does.