The term "cancerous tumor" refers to a type of abnormal growth that occurs when cells in a part of the body start to grow and divide uncontrollably. These cells can form a mass called a tumor, which may be cancerous if it is malignant - meaning it has the potential to spread (metastasize) to other parts of the body. Cancerous tumors are generally considered dangerous because they can invade surrounding tissues and organs, as well as disrupt normal bodily functions. Treatment for cancer often involves surgery, radiation therapy or chemotherapy to remove or destroy the cancer cells.