Introduction to Cancer

Abstract

The existence of cancer has been known to man since ancient times; however, recovery from this disease was rare through the nineteenth century. Since 1900, numerous cancer research programs, particularly those at the National Cancer Research Institute in the United States, have contributed to an explosion of knowledge in oncology which includes such areas as etiology, pathophysiology, detection, and treatment of cancer. Examination of cancer-related statistics reveals that, in the United States, the odds of contracting this disease are 1 in 2 for men and 1 and 3 for women. 1,268,000 cases were expected to be diagnosed in 2001 and 533,400 deaths due to cancer were projected to occur. The most common cancers in men are prostate, lung and bronchus, colon and rectum. In women, the most common cancers are breast, lung and bronchus, colon and rectum. Approximately 8,600 new cases of cancer were projected to occur in children age 0-14 in 2001. Common sites in children include the blood, bone marrow, lymph nodes, brain, sympathetic nervous system, kidneys and soft tissues. The 5-year relative survival rate for all cancers combined is 60% after adjusting for normal life expectancy (factors such as dying of heart disease, accidents and diseases of old age). The relative 5-year survival rate represents persons who are living five years after diagnosis, whether disease free, in remission or under treatment with evidence of cancer. Relative survival does not reflect the proportion of people who are cured permanently and live longer than five years after diagnosis. Cancer is a complex series of diseases characterized by an uncontrolled proliferation of cells into masses, referred to as malignant neoplasm or malignant tumors. Metastasis occurs when some tumor cells leave the site of tumor origin and travel to other parts of the body. Although many attempts have been made to classify these diseases in a logical system, unfortunately, most of these systems have become obsolete as knowledge of cancers has increased. The classification system described here is based on the histohenesis, or the presumed tissue of origin of the cancer. Some aspects of this classification are related to the three layers of cells formed in the young embryo: 1. Ectoderm: Cells which form the outer layer of embryonic tissue. The following parts of the body arise from this layer: skin, epidermal tissue, fingernails, hair, skin glands, mucous membranes of mouth and anus, sensory organs, (i.e., eyes ears), nervous tissue (i.e., brain and spinal cord) 2. Mesoderm: The middle cell of embryonic tissue which forms bone, connective tissue, muscle, blood, vascular and lymphatic tissue. 3. Endoderm: The innermost embryonic cell layer which gives rise to the epithelial cells which line digestive and respiratory tracts. See Figure 1.