The cells divide uncontrollably and may grow into adjacent tissue or spread to distant parts of the body. The accumulation of tumor cells eventually become large enough to produce lumps, masses, or tumors that can be detected. Cancers cause problems because they grow and occupy space, sometimes pushing on other structures and causing them to malfunction. They may also erode into other structures and bleed. Cancers have no nerves so they do not hurt, but they can cause other structures to hurt because of the destruction or pressure on the normal structures.
Cancers require energy to grow and rob the body of the energy it needs for normal function.
Adenocarcinomas are cancers that form on a glandular surface, such as the lung, breast, prostate, ovary, or kidney. Sarcomas are cancers that occur in supporting structures, such as bone, muscle, cartilage, fat, or fibrous tissue. Leukemias and lymphomas are cancers that occur in blood cell elements. Brain cancers , nerve cancers , melanomas , and certain testicular and ovarian cancers do not fall into a general category. Cancers begin in a single cell, and that cell is the site of the primary cancer.