A tumor describes any discrete body of cells in or on a human body where cell growth is unregulated and the body grows without any regard for the body's other tissues. Tumors can either be malignant (cancerous) or benign. Benign tumors are usually not a threat to health, but can grow to appreciable size. Malignant tumors can metastasize - throw off cells which can form new tumors elsewhere in the body.
Wherever possible, tumors are removed surgically. However, this is not an option for tumors in certain parts of the body, particularly the brain. As such, once a biopsy has confirmed that a tumor is benign, such tumors are usually left alone. Malignant tumors that are inoperable have to be treated with chemotherapy or radiation therapy.
Tumors are usually attached to a discrete part of the body, rather than being found generally in muscle tissue. As such, where there are other signs of cancer, organs such as the brain, lungs, ovaries, testicles, bones, liver and kidney are searched for tumors, either with radiology or exploratory surgery.