What is a cancer

   Cancer is not a single disease, but takes more than 100 forms, all of which are characterized by a multiplication of cells that threaten life. In this sense, the term neoplasm, or new growth, is most fitting. In most types, a tumor, or enlarging mass, develops as a result of a steady and abnormal multiplication of cells. Cell multiplication that is restricted to a single site is called a benign tumor.  When the multiplying cells invade adjoining tissues, or when they are carried in body fluids (blood, lymph) to other parts of the body, the mass is called a malignant tumor, or carcinoma.  Thus the most common medical terms used to designate a cancer are malignant tumor, malignant growth, neoplasm, or carcinoma. 

   All but the most highly specialized cells of the body can replace themselves when worm out, injured, or aged. The superficial cells of the skin, and hose lining the intestinal tract and the uterus, are constantly being rubbed or sloughed off. New cells forming in the deeper layers replace those that are lost, thus maintaining a constant balance between loss and renewal.

    This is also true of blood cells. Red blood cells live for about 120 days. Each second some two to three million worm-out red corpuscles are taken out of circulation by the spleen. At the same time, a similar number of new red blood cells enter the circulatory system from the bone marrow, where they are manufactured. White blood cells always increase in number under the stimulus of an infection, but the body will return to a normal production level when the infection is over.

   Normally, the human body maintains a precise control over the number of cells that make up its tissues, so that it produces only the cells that it needs. When the required number is reached, cell production stops. This control over cell production resides in the genes that are found in the nucleus of each cell. The DNA molecules in the genes are "coded" to regulate how each cell grows and the work it does, thus enabling every cell in the body to work in cooperation with all other cells. As the body grows, beginning at conception and continuing to adulthood, the number of cells increases enormously, but the rate of increase is always controlled very carefully so that only the proper number of each cell is produced.

   In a cancer cell, though, the DNA molecules have been altered or rearranged in subtle ways hat change them into what we call "oncogenes," or cancer genes. The oncogene calls in a developing neoplasm or cancer multiply in spite of the body's normal checks and balances. The body loses control of its cell growth, and the cancer cells no longer obey the signal to stop growing.