Metastasis
The spread of cancer from its original site to a distant part of the body.
What it means
Metastasis is the spread of malignant cells from a primary tumour to a distant site, travelling through the bloodstream or lymphatic system. The resulting deposit is a metastasis, or secondary.
An important point frequently misunderstood: a metastasis retains the identity of the original cancer. Breast cancer that has spread to bone is metastatic breast cancer, not bone cancer, and it is treated as breast cancer.
The capacity to metastasise is what distinguishes malignant from benign growths.
In practice
Reported on staging scans and in oncology letters, abbreviated to "mets". The TNM staging system records tumour size, lymph node involvement and metastasis.
Certain cancers have characteristic patterns of spread, which determines which scans are performed.
Why it matters
Metastatic disease is generally not curable, but it is frequently treatable, and outcomes in several cancers have improved substantially.
The word describes the extent of disease, not a prognosis in itself — which varies enormously by cancer type and by the treatments available.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
August 30, 2026