What Is Cancer?
The millions of cells that make up the body normally reproduce in an orderly manner, replacing worn-out tissues and repairing injuries to maintain health. However, certain cells may begin to reproduce abnormally, massing together to form tumors.
If a tumor is benign, it will remain self-contained. A malignant–or cancerous–tumor, on the other hand, will invade neighboring tissues, and can spread through the blood and lymphatic systems to distant parts of the body in a process called metastasis.
Cancer is not one disease, but rather many related diseases. Cancer is typed according to the part of the body where it is located and the kind of cells that comprise it. The most common types of cancer cells and their locations are:
* Carcinomas originate in skin tissue or tissues that line the body cavities and such internal organs as the lungs, breast, colon, and intestines.
* Sarcomas grow in bones and connective tissues between organs and skin, and sometimes spread into the blood or lymphatic system.
* Lymphomas are cancers of the lymphatic system, usually occurring in the lymph nodes.
* Leukemias form in the blood or circulatory system, particularly in the bone marrow, which is the site of blood cell production.
* Myelomas are tumors of bone marrow cells and frequently form simultaneously in many sites, including the ribs, vertebrae, and pelvic bones.
Cancer is treated by surgery, chemotherapy, radiation, or a combination of these methods. Diagnoses and treatment have become increasingly individualized in recent years. Early detection and the precise staging of therapies have contributed to higher success rates in the battle against cancer.
Many cancers that only recently had poor prognoses are now considered curable. Potentially curable cancers now include acute lymphocytic leukemia in children, Burkitt’s lymphoma, Ewing’s sarcoma (a form of bone cancer), Wilm’s tumor (a kidney cancer in children), Hodgkin’s disease, rhabdomyosarcoma (a cancer of certain muscle tissues), testicular cancer, choriocarcinoma (placental cancer), osteogenic sarcoma, and breast cancer.
Current developments also show the promise of improved treatment for many other forms of cancer. For example, the recently discovered importance of oncogenes–the genes in a tumor cell that are associated with the transformation of normal cells into cancerous ones–promises to help predict which tumors are likely to return after surgery. This knowledge can also help identify family members who are at risk.