Cancer

There is also a constellation named Cancer: see Cancer (constellation).
In medicine, cancer is a general term for any of a number of different diseases where some of the body's own cellss divide in an uncontrolled manner. The resulting new cells can form a malignant tumor (a neoplasm) or propagate throughout the body.

Table of contents
1 Biology of malignant tumors
2 Forms of cancer
3 Clinical aspects
4 Cure for Cancer Agencies
5 See also

Biology of malignant tumors

Carcinogenesis

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; Bacteria, like Helicobacter pylori, also induce carcinogenesis by a process of chronic inflammation. 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 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.

Malignant tumors such as carcinoma or sarcoma, lymphoma or leukemia originate from a cell or a group of cells in a multicellular organism that has several distinct properties:

  • evading apoptosis
  • Unlimited Growth Potential
  • self-sufficiency of growth factors
  • insensitivity to anti-growth factors
  • increased cell division rate
  • altered differentiation (specialization) ability
  • no ability for contact inhibition
  • ability to invade neighbouring tissue
  • ability to build metastases
  • ability to promote blood vessel growth (angiogenesis)

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

Cancers are capable of spreading through the body by two mechanisms: local invasion and distant 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.

Forms of cancer

The term cancer is very broad and covers many different illnesses including:

Clinical aspects

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 abovementioned 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.

Treatments

Cure for Cancer Agencies

Below is a list of some well-known institutions dedicated to funding cancer research that would eventually lead to a cure for cancer:
  • Yorkshire Cancer Research
  • Canadian Cancer Society
  • American Cancer Society
  • BC Cancer Agency
  • National Cancer Institute
  • International Agency for Research on Cancer

See also

List of cancer patients -- Apoptosis -- Oncogene -- Tumor suppressor gene


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