In medicine, cancer is a general term for any of a number of different diseases where some of the body's own cells divide in an uncontrolled manner. The resulting new cells can form a malignant tumor (a neoplasm) or propagate throughout the body.
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Carcinogenesis is the creation of a cancer.
Cancer is, ultimately, a disease of genes. Typically, a series of several mutations is required before a cell becomes a cancer cell. We distinguish between oncogenes, which promote cancer when "switched on" by a mutation, and tumor suppressor genes, which prevent cancer unless "switched off" by a mutation. These mutations can have various causes: radiation or chemicals called carcinogens; some inherited predisposition is not uncommon; some viruses that can cause cancer have also been described. Usually, they carry in their genome some oncogene or tumor suppressor inactivating gene. In about 15% of all cancers, viruses seem to play a role. Finally, damage by free radicals, which are a natural by-product of oxygen metabolism, can cause mutations in the DNA.
For most of the cancers, it cannot be told which event was the initial cause. However, with molecular biology, it is possible to characterize the mutations within a tumor, and to a certain extent to predict its behavior. For example, about half of the tumors are deficient in the tumor suppressor gene p53, also known as "the guardian of the genome". This is associated with poor prospects for the patient, since those tumor cells are unlikely to go into apoptosis (programmed cell death) after they are damaged by therapy. There are more mutations that make a tumor more malignant. Telomerase mutations enable a tumor cell to divide indefinitely. Other mutations enable the tumor to grow new blood vessels to feed it, or to detach from the surrounding tissue, spreading to other parts of the body.
- increased cell division rate
- not controllable by growth factors anymore
- altered differentiation (specialization) ability
- no ability for contact inhibition
- ability to invade neighbouring tissue
- ability to build metastases
- ability to promote blood vessel growth
A cell that degenerates into a tumor cell does usually not acquire all these properties at once, but its daughter cells are selected to build them. This process is called cellular evolution. A first step in the development of a tumor cell is usually a small change in the DNA, often a point mutation, which leads, among other things, to a genetic instability of the cell. The instability increases to a point where the cell loses whole chromosomes, or has double ones. Also, the DNA methylation pattern of the cell changes, activating and deactivating genes more or less at random. Cells that divide at a high rate, such as stem cells, show a higher risk of becoming tumor cells than those which divide less or not at all, for example, neurons. If the initial tumor cell (or group of tumor cells) is not removed by the immune system, it will develop into cancer.
In cellular model systems, cells are exposed to carcinogenic influences (chemicals, radiation). In these systems, the first signs of a cell developing into a tumor cell are :
- Immortality. The usual number of cell divisions for a mammalian cell is 50-60 (cell senescence), then it ceases to divide. Tumor cells keep dividing forever.
- Altered morphology.
- Building of cellular clusters (Foci).
- Loss of contact inhibition.
- Low or no need for growth factors.
metastasis. Invasion refers to the direct migration and penetration by cancer cells into neighboring tissues. Metastasis refers to the ability of cancer cells to penetrate into lymphatic and blood vessels, circulate through the bloodstream, and then invade normal tissues elsewhere in the body. Cancer is most deadly when it metastasizes.
- Bladder cancer
- Bone cancer
- Brain tumor
- Breast cancer
- Cervical cancer
- Colorectal cancer (includes colon, rectum, anus, and appendix)
- Cancer of the esophagus
- Hodgkin's disease
- Kidney cancer
- Cancer of the larynx
- Liver cancer
- Lung cancer
- Moles and dysplastic nevi
- Multiple myeloma
- Muscular Cancer
- Non-Hodgkin's lymphoma
- Oral cancer
- Ovarian cancer
- Cancer of the pancreas
- Prostate cancer
- Skin cancer
- Stomach cancer
- Testicular cancer
- Thyroid cancer
- Cancer of the uterus
The field of medicine concerned with the treatment of cancer is oncology.
Cancer has become an important problem with the rise in life expectancy, as the above mentioned mutations become more likely the longer a person lives. Though great progress in treatment has been made, most cancers in advanced stages remain incurable and ultimately fatal.
Treatment of cancer typically involves surgery to remove tumors and nearby lymph nodes to which the cancer may have spread, combined with radiation therapy and/or chemotherapy. The latter two target cells in the body that are rapidly dividing. This includes the cancer cells but also certain healthy ones, which is the reason for the severe side effects of these treatments.