metastatic

Metastatic is a descriptor used in oncology to characterize cancer that has spread from its original site to distant organs or tissues. A metastatic tumor consists of cells that have disseminated from the primary neoplasm and established new foci apart from the original location. In clinical practice, metastasis is categorized in staging systems, often designated as M1 in the TNM system, indicating distant spread.

Metastasis involves multiple steps: local invasion of surrounding tissue, entry into blood vessels or lymphatics (intravasation), survival of circulating tumor cells, exit from the circulation (extravasation), and colonization of distant organs. The pattern of spread depends on tumor biology and the microenvironments of potential target organs, a phenomenon sometimes described as organotropism.

Common sites of metastatic spread vary by cancer type. For example, breast cancer frequently involves bone, liver, lung, and brain; colorectal cancer commonly metastasizes to the liver; prostate cancer often spreads to bone.

Diagnosis usually requires imaging such as computed tomography, magnetic resonance imaging, or positron-emission tomography, followed by biopsy of a suspected metastatic lesion to confirm histology and receptor status when applicable.

Treatment of metastatic cancer is typically systemic, including chemotherapy, targeted therapy, endocrine therapy, and immunotherapy. Local treatments, such as surgery or radiotherapy, may be used to alleviate symptoms or control specific metastatic sites, depending on disease burden, location, and biology. The goal is often palliation and prolongation of life rather than cure, though occasional cases of long-term control are possible with exceptional responses.

Prognosis varies widely by cancer type and extent of disease. Ongoing research aims to understand metastatic mechanisms, improve detection (including liquid biopsies), and develop therapies to prevent or limit spread.