Metastasis
Metastasis is the spread of cancer cells from a primary tumor to distant parts of the body, where they can form secondary tumors.
Invasion–metastasis cascade: The sequence of cellular steps by which cancer cells invade surrounding tissue, travel, and establish distant tumors. It organizes metastasis into stages, including local invasion, circulation, exit, and growth.
Clonal evolution: The process by which genetic and epigenetic differences among cells lead populations to change over time through selection. Metastases often arise from selected subpopulations within a genetically diverse primary tumor.
Cancer staging: The classification of cancer extent, including tumor size, lymph-node involvement, and distant spread. Metastasis determines the distant-spread component of staging and often changes treatment plans.
Local invasion: The growth of cancer cells into nearby tissues from their site of origin. Invasion is a necessary early step for many metastases, but it does not itself mean distant spread.
Oligometastatic disease: A state of cancer with a limited number of detectable metastatic lesions. Some cases with few lesions can be treated with focused local therapies as well as systemic treatment.
Epithelial–mesenchymal transition: A cellular program in which epithelial cells acquire traits associated with motility and reduced cell-to-cell adhesion. Some cancer cells use EMT-associated traits to detach and invade, though metastasis does not require a complete transition.
Tumor heterogeneity: The variation in genetic, molecular, and behavioral traits among cells within a tumor. Different tumor-cell states have different capacities to spread, survive, and grow.
TNM classification: A cancer staging system describing the primary tumor, regional lymph nodes, and distant metastasis. Its M category records whether cancer has spread to distant sites.
Carcinoma in situ: A malignant epithelial growth confined to its original tissue layer without invasion through the basement membrane. By definition, it has not invaded tissues or spread to distant sites.
Bone metastasis: The growth of cancer that spread from another site within bone tissue. It can cause pain, fractures, and other skeletal complications.