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Cancer that spreads beyond its site of its origin. Metastasis may be local (extend outside the original tumor but remain near the original site), regional (remain in the general vicinity of the original site), or distant (in organs or tissues elsewhere in the body from the original site). It may occur as a result of direct invasion of adjacent tissues and organs or when cancer cells enter the LYMPH or BLOOD circulation. A metastasized cancer retains the characteristics of the tumor of origin.
For example, PROSTATE CANCER that metastasizes to the bone is metastatic prostate cancer, not BONE CANCER. The type of cancer is an important factor in determining the most effective treatment. The LUNGS, LIVER, and bone are the most common sites for metastasis. Cancer that comes back after treatment is a RECURRENCE. Metastasis may be evident at the time of diagnosis or may occur after treatment.