There are many different types of cancer.  Several factors, including location and how the cancerous cells appear under the microscope, determine how cancer is diagnosed.  For example, there are several forms of breast cancer, classified according to where the tumors originate within the breast, and their tendency to invade surrounding organs and tissue. All cancers, however, fall into one of four broad categories:

Carcinomas are tumors that arise in the tissues that line the body's organs. About 80% of all cancer cases are carcinomas.

Sarcomas are tumors that originate in bone, muscle, cartilage, fibrous tissue or fat.

Leukemias are cancers of the blood or blood-forming organs.

Lymphomas affect the lymphatic system, a network of vessels and nodes that acts as the body's filter. The lymphatic system distributes nutrients to blood and tissue, and prevents bacteria and other foreign "invaders" from entering the bloodstream.   There are over 20 types of lymphoma.