Evolution and Cancer

Jonathan Wells wrote a paper a while back that proposed a "ID-derived" explanation for cancer. I've written about that before (here, here , here, here, and here) as have others. Thus, this is of interest:

In a study published online today in Nature Genetics, Carlo Maley, Ph.D., a researcher at The Wistar Institute, and his colleagues report that precancerous tumors containing a population of highly diverse cells were more likely to evolve into cancer than those containing genetically similar cells. The finding suggests that, in at least some forms of cancer, the more genetically diverse a precancerous tumor is, the more likely that tumor is to progress to full-blown cancer. If so, genetic diversity might act as a biomarker for cancer risk among patients with precancerous tissues.

"Although researchers first defined cancer in evolutionary terms in the 1970s, few researchers have actually studied the disease this way," says Maley, lead author on the study and an assistant professor in the molecular and cellular oncogenesis program at Wistar. "We wanted to know: If we measured a precancerous tumor's genetic diversity at baseline, could we predict who would go on to get cancer?" ...

Maley suggests that genetically diverse tumors have a high probability of generating mutant cells that will flourish and spread, allowing the tumor to transform and grow. In the future, in addition to serving as a biomarker for cancer risk, he adds, measures of genetic diversity might help doctors assess the success of cancer prevention therapies.

In fact, he speculates, genetic diversity among tumor cells might help explain why therapy sometimes fails. If a tumor contains a diverse population of cells, some of those cells are more likely to resist treatment, Maley says. Adapting to and surviving chemotherapy, these resistant cells could breed, leading to a cancer relapse. He hopes to pursue this hypothesis in the future. "More immediately," he adds, "we intend to validate the new study with other cohorts and other types of tumors."

Read more in the press release.

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In one way, this is actually rather old news. It's been known for a long time that genetic instability (which leads to increased genetic diversity in tumors) leads to faster chemoresistance and more aggressive malignant tumors. The novelty of the study is that it was applied to premalignant lesions.

I am assuming that by 'genetic diversity' they mean diversity of cell types, i.e., diversity of patterns of gene expression. After all, all the cells in one body have exactly the same genome.

This post reminds if of another pseudoscientific connection between cancer and evolution - the book "Cancer Selection" by one James Graham. There is rich material in there for at least a dozen long blog posts destroying one chapter at a time (but sho has the tiem to waste on it?!). Curiously, he superposes some pieces of correct information together in novel ways that may be insightful and enlightening, even though he takes wrong messages out ot the excercise.

You're correct when it comes to normal cells, but part of what drives cancer is genetic instability. However, cancer cells do not all share the same genome from which they were derived. They undergo mutation, chromosomal rearrangement, gene amplification, etc., such that the genomes of different clones of cancer cells can be quite different. True, they are still human genomes, but they have undergone considerable change.