metastases

Metastases are secondary cancerous growths that arise when cells from a primary tumor spread to distant sites and establish new tumors. The metastatic cascade consists of local invasion, intravasation into blood or lymphatic vessels, survival in circulation, arrest at distant organs, extravasation into the tissue, and colonization to form macroscopic metastases.

Common sites of metastasis include bones, liver, lungs, and brain, with specific patterns depending on the primary cancer type (for example, breast cancer frequently affects bone and liver; colon cancer commonly spreads to the liver). The presence of distant metastasis is denoted M1 in cancer staging, while M0 indicates no distant spread. Diagnosis typically involves imaging such as CT, MRI, and PET, and may require biopsy of a metastatic lesion; histology usually resembles the primary tumor.

Treatment often relies on systemic therapies—chemotherapy, targeted therapy, hormonal therapy, and immunotherapy—to control disseminated disease. Local therapies such as metastasectomy, stereotactic radiotherapy, or palliative radiotherapy may be used to relieve symptoms or control specific metastases. Prognosis varies by cancer type, extent of metastasis, and patient factors; metastasis generally worsens outlook but some cancers remain controllable for extended periods with effective systemic therapy.

Metastases are named after the primary cancer type rather than the site of spread (for example, metastatic breast cancer to bone). Distinguishing metastases from a second primary tumor is essential for treatment planning and prognosis.