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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.
Items 2-4 (above) can sometimes be traced to mutations in genes that result in a disruption of cell adhesion. Some cell adhesion proteins are oncogenes.
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)
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.
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- NetCancerAlert
Provides access to articles and links which are oncology related. - CancerExperts MD
Physcians located in Boston offer second opinions and personalized case reviews. Provides an online ask-a-doctor service. - EMedicine Health: Cancer Symptoms
Consumer health resource center providing information on common symptoms. - Conversations In Care
Explores the challenges surrounding physician and patient communications in cancer. - Nature: Cancer Update
Service which provides access to news articles and reports about recent research activity. Registration required.