Metastasis is the term used to describe a situation where a malignant tumor recurs in different parts of the body. The appearance of metastases occurs when cancer cells detach from the primary tumor and enter the bloodstream or lymphatic system and can circulate throughout the body and settle in another organ.
When spreading through the body and forming a tumor focus on another organ, away from the primary site or place of origin of the disease, this new tumor is called metastatic. For example, a patient diagnosed with breast cancer (primary site) that some time later discovers a lung nodule should have this nodule investigated to know its origin. If the biopsy shows breast cancer-compatible cells (and a variety of analysis techniques are used to determine the origin), we are dealing with metastatic cancer rather than lung cancer. This metastatic cancerous lump in the lung is made up of breast cancer cells.
