Cancer appears to develop through a series of events, when a cell divides, its chromosomal material, consisting largely of very complex molecules of deoxyribonucleic acid (DNA) also divides, providing each daughter cell with chromosomal material identical to that of the original. Some of the daughter cells continue to divide, while others differentiate to perform special functions. If chromosomal material is affected by a carcinogen (cancer-promoting agents) or some other factor, the resulting abnormal chromosome will be passed on to succeeding generations of cells, destroying the well-ordered system of cell division. Malignantly transformed cells will fail to differentiate and will continue to reproduce, a process that marks the beginning of a malignant tumor.

Classification of Cancer: Cancer are classified according to the type of tissue in which the cancer originates and the location in the body where the cancer first developed.

• Carcinoma is a malignancy that arises in the skin, the lining of various organs, or glandular organs or tissues. Most carcinomas affect organs or glands capable of secretion, such as the breasts, lungs colon, prostate and bladder.
• Sarcoma is a malignancy arising in bone, muscle, or connective tissue. The most common sarcoma often develops as a painful mass on the bone.
• Leukemia, a neoplastic disease of the white blood cells, arises in bone marrow. Leukemia is commonly classified into acute and chronic forms. These are further broken down according to the type of white blood cells affected by the disease.
• Lymphoma develops in the glands or nodes of the lymphatic system, a network of vessels, nodes, and organs that purify bodily fluids and produce infection-fighting white blood cells or lymphocytes.