Natural Selection in Cancer
Cells in pre-malignant and malignant neoplasms (tumors) evolve by natural selection. This accounts for how cancer develops from normal tissue and why it has been difficult to cure. There are three necessary and sufficient conditions for natural selection, all of which are met in a neoplasm:
- There must be variation in the population. Neoplasms are mosaics of different mutant cells with both genetic and epigenetic changes that distinguish them from normal cells.
- That variation must be heritable. When a cancer cell divides, both daughter cells inherit the genetic and epigenetic abnormalities of the parent cell, and may also acquire new genetic and epigenetic abnormalities in the process of cellular reproduction.
- That variation must affect survival or reproduction (fitness). While many of the genetic and epigenetic abnormalities in neoplasms are probably neutral evolution, many have been shown to increase the proliferation of the mutant cells, or decrease their rate of death (apoptosis). (See Hallmarks below)
Cells in neoplasms compete for resources, such as oxygen and glucose, as well as space. Thus, a cell that acquires a mutation that increases its fitness will generate more daughter cells than competitor cells that lack that mutation. In this way, a population of mutant cells, called a clone, can expand in the neoplasm. Clonal expansion is the signature of natural selection in cancer.
Cancer therapies act as a form of artificial selection, killing sensitive cancer cells, but leaving behind resistant cells. Often the tumor will regrow from those resistant cells, the patient will relapse, and the therapy that had been previously used will no longer kill the cancer cells. This selection for resistance is similar to the repeatedly spraying crops with a pesticide and selecting for resistant pests until the pesticide is no longer effective.
Read more about this topic: Somatic Evolution In Cancer
Famous quotes containing the words natural, selection and/or cancer:
“There is natural ignorance and there is artificial ignorance. I should say at the present moment the artificial ignorance is about eighty-five per cent.”
—Ezra Pound (1885–1972)
“Judge Ginsburg’s selection should be a model—chosen on merit and not ideology, despite some naysaying, with little advance publicity. Her treatment could begin to overturn a terrible precedent: that is, that the most terrifying sentence among the accomplished in America has become, “Honey—the White House is on the phone.””
—Anna Quindlen (b. 1952)
“I’m beginning to believe that Killer Illiteracy ought to rank near heart disease and cancer as one of the leading causes of death among Americans. What you don’t know can indeed hurt you, and so those who can neither read nor write lead miserable lives, like Richard Wright’s character, Bigger Thomas, born dead with no past or future.”
—Ishmael Reed (b. 1938)