Cell division or cell proliferation is a physiological process that occurs in almost all tissues and under many circumstances. Normally the balance between proliferation and programmed cell death is tightly regulated to ensure the integrity of organs and tissues. Mutations in DNA that lead to cancer disrupt these orderly processes.
The uncontrolled and often rapid proliferation of cells can lead to an initially benign tumor but it may carry a risk of turning malignant (cancer). Benign tumors do not spread to other parts of the body or invade other tissues, and they are rarely a threat to life unless they extrinsically compress vital structures. Malignant tumors can invade other organs, spread to distant locations (metastasize) and become life-threatening.
The process of malignancy can be explained from an evolutionary perspective. Once a turmor becomes established it functions as an independent target of natural selection. Cells with mutations that promote their own growth and proliferation are likely to be favored over their less invasive neighbors. Possible mutations include the ability to grow fast, the ability to tap into blood vessels and the ability to migrate. If these mutant strains come to dominate the clone the tumor may progress towards a malignant status.
Normal cells have the same invasive and proliferative capabilities as cancer cells but their regulatory mechanisms hold them in check except at appropriate times. The chances of such complex abilities arising anew from a few mutation events is vanishingly slim. For this reason the alterations in cancer cells are typically defects in regulatory genes.The outcome depends on a number of factor including exposure to mutagens and the immune competence of the host. A few types of cancer in non-humans have been found to be contagious ("parasitic cancer"), such as Sticker's sarcoma, which affects dogs. The closest known analog to this in humans is individuals who have "caught cancer" from tumors hiding inside organ transplants.
The uncontrolled and often rapid proliferation of cells can lead to an initially benign tumor but it may carry a risk of turning malignant (cancer). Benign tumors do not spread to other parts of the body or invade other tissues, and they are rarely a threat to life unless they extrinsically compress vital structures. Malignant tumors can invade other organs, spread to distant locations (metastasize) and become life-threatening.
The process of malignancy can be explained from an evolutionary perspective. Once a turmor becomes established it functions as an independent target of natural selection. Cells with mutations that promote their own growth and proliferation are likely to be favored over their less invasive neighbors. Possible mutations include the ability to grow fast, the ability to tap into blood vessels and the ability to migrate. If these mutant strains come to dominate the clone the tumor may progress towards a malignant status.
Normal cells have the same invasive and proliferative capabilities as cancer cells but their regulatory mechanisms hold them in check except at appropriate times. The chances of such complex abilities arising anew from a few mutation events is vanishingly slim. For this reason the alterations in cancer cells are typically defects in regulatory genes.The outcome depends on a number of factor including exposure to mutagens and the immune competence of the host. A few types of cancer in non-humans have been found to be contagious ("parasitic cancer"), such as Sticker's sarcoma, which affects dogs. The closest known analog to this in humans is individuals who have "caught cancer" from tumors hiding inside organ transplants.
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