CLASSIFICATION OF CANCER TYPES
Cancers are often classified according to their tissue of origin. Thus, a carcinoma is derived from epithelial tissue, whereas a sarcoma is derived from tissue of mesodermal origin such as muscle, bone or cartilage. The term leukemia refers to tumors of the bone marrow that result in excess cells of a single type appearing in the blood. Lymphoma refers to a tumor which arises from lymphoid tissue, such as a lymph node. There is also a group of highly malignant tumors that occur in childhood, which all have the suffix ‘blastoma’. These include neuroblastomas, which arise in the neuroblasts of the adrenal medulla, retinoblastoma, which originates in the retina of the eye, and nephroblastoma, derived from the embryonic cells of the kidney.