Cancer is a class of diseases characterized by out-of-control cell
growth. There are over 100 different types of cancer, and each is
classified by the type of cell that is initially affected.
Cancer harms the body when damaged cells divide uncontrollably to form
lumps or masses of tissue called tumors (except in the case of leukemia
where cancer prohibits normal blood
function by abnormal cell division in the blood stream). Tumors can grow
and interfere with the digestive, nervous, and circulatory systems, and
they can release hormones that alter body
function. Tumors that stay in one spot and demonstrate limited growth
are generally considered to be benign.