Tumor originally just meant "swelling", but the term is very often used to denote abnormal (malignant or benign) growth of tissue. Malignant tumors (cancer) invade and destroy neighboring tissues and can become metastatic. Benign tumors do not invade neighboring tissues and do not seed metastases, but may locally grow to great size.

See also : Apoptosis -- Oncogene -- Tumor suppressor gene -- Carcinoma -- Sarcoma -- Lymphoma -- Leukemia