Cancer begins when cells in the body divide unnecessarily and accumulate to form a tumor. Tumors can be either a mass of tissue, called "solid cancer," or a collection of cells in the bloodstream, called "hematological cancer." Most cancers are named for the organ or type of cell in which they begin. For example, cancer that begins in the breast is breast cancer, and cancer that begins in the colon is colon cancer. Sometimes, cells from the original tumor spread to other parts of the body. When this spreading occurs, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. If cells from breast cancer spread to the lung and form a tumor, the patient is still considered to have breast cancer, not lung cancer.