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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.

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.

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)

  • Romanian Cancer League
    Eastern European organization with aims of education, prevention, treatment, support and advocacy.
  • Cancerlinksusa.com
    Information and links for all types of tumors.
  • Manage CINV
    Offers patients and professionals information about chemotherapy-induced nausea and vomiting.
  • CancerCare
    Topics of interest to patients and their families including treatment side-effects, pain control, nutrition and bereavement.
  • Hologuides: Cancer
    Information about various tumors in a links format.