Cancer, is a disease of the cell cycle. Unlike normal cells of the body, cancer cells do not have a properly functioning cell-cycle control system and therefore divide excessively. This excessive growth can result in an abnormal mass of cells called a tumor. Not all tumors are cancerous, however, a benign tumor is an abnormal mass of essential normal cells. Benign tumors can cause problems if they grow in certain organs, such as the brain but usually they can be completely removed by surgery. They always remain at their original site in the body.
|Formation of Cancer|
In contrast to a benign tumor, a malignant tumor is cancerous. It is a mass of cancer cells, which are capable of spreading into neighboring tissues and often to other parts of the body. A malignant tumor arises from a single cancer cell and displaces normal tissue as it grows. If the tumor is not killed or removed, some of the cancer cells spread into surrounding tissue, enlarging the tumor. Cells may also split off from the tumor, invade the circulatory system (lymph vessels and blood vessels), and travel to new locations, where they can form new tumors. The spread of cancer cells beyond their original site is called metastasis.
Cancers are named according to the organ or tissue in which they arise, and over 200 different types are recognized in humans. For simplicity they are grouped into four categories. Carcinomas are cancers that originate in the external or internal coverings of the body; such as the skin or the lining of the intestine. Sarcomas arise in tissues that support the body, such as bone and muscle. Cancers of blood-forming tissues, such as bone marrow, spleen are called leukemias and that of lymph nodes are called lymphomas. Cancer cells can go on dividing indefinitely, as long as they have a supply of nutrients. If cancer cells stop dividing, they seem to do so at random points in the cell cycle, rather than just at the normal cell-cycle checkpoints.
Two types of cancer treatment, chemotherapy and radiation therapy, attempt to halt the spread of cancer cells by stopping them from dividing. In radiation therapy, parts of the body that have cancerous tumors are exposed at high-energy radiation, which disrupts cell division. Chemotherapy uses the same strategy as radiation; in this case, drugs that disrupt cell division are administered to the patient.
Cancer cells can be distinguished from normal cells because they have high nucleus to cytoplasm ratio, prominent nucleoli and many mitosis. The presence of invading cells in otherwise normal tissue is an indication of malignancy. Cancer is caused mainly by mutations in somatic cells. Secondary, the cancer results from the accumulation of a few as three to as many as twenty mutations, in genes that regulate cell division.
Characteristic of Cancer Cells
At the least four features characterize all cancer cells.
(1) Their plasma membrane and cytoplasm change profoundly.
(2) Cancer cells grow and divide abnormally.
(3) Cancer cells have a weakened capacity for adhesion.
(4) Cancer cells are lethal.