1) Modern conventional medicine (western medicine)
The following information is based on the American Medical Association Encyclopedia of Medicine.
Cancer is any of a group of diseases in which symptoms are due to the unrestrained growth of cells in one of the body organs or tissues. Most commonly, malignant tumors develop in major organs, such as the lungs, breasts, intestines, skin, stomach, or pancreas, but they may also develop in the nasal sinuses, the testes or ovaries, or the lips or tongue. Cancers may also develop in the blood cell-forming tissues of the bone marrow (leukemia) and in the lymphatic system, muscles, or bones. Cancer is the second most common cause of death in the US, accounting for about one fifth of the total (the most common is heart disease).
Cancers are not the only type of abnormal growth, or neoplasm, which occurs in the body. However, cancer differs from a lipoma in two important ways. As cancer grows, it spreads and infiltrates the tissues around it and may block passageways, destroy nerves, and erode bone. Cells from the cancer may spread via the blood vessels and lymphatic channels to other parts of the body, where these metastasize and form new, satellite tumors that grow independently.
Cancer is a process that has affected humans since prehistoric times and is also common in domestic and farm animals, birds, and fish. Apart from childhood cancers, which may be associated with events during pregnancy, such as exposure to radiation, most cancers are a feature of aging.
The growth of a cancer begins when the oncogenes (genes controlling cell growth and multiplication) in a cell or cells are transformed by agents known as carcinogens.
Once a cell is transformed into a tumor-forming type (malignant transformation), the change in its oncogenes is passed on to all offspring cells. A small group of abnormal cells is thus established, and they divide more rapidly than the normal surrounding cells. Usually the abnormal cells show a lack of differentiation – that is, they no longer perform the specialized task of the cells of their host tissue – and may escape the normal control of hormones and nerves. Thus, they are in effect parasites, contributing to consume nutrients.
Years may pass before the growth of cells becomes large enough to cause symptoms, although the rate of growth varies according to the tissue of origin. Current estimates suggest that some cancers of the lung and breast have been present for more than five years before they cause symptoms. During this period of time, metastasis may be seeded in the liver, lungs, bones, or brain, and in these circumstances, surgical cure is impossible because the cancer has already spread far beyond the primary site of origin.