Unluckiness Is A Leading Cause Of Cancer

Cancer And Luck

That’s what a study released last week found:

Bert Vogelstein and Cristian Tomasetti of Johns Hopkins University have put forth a mathematical analysis of the genesis of cancer that suggests many cases are not preventable. Drawing on the published literature, they estimated the number of cells in an organ, what percentage of them are long-lived stem cells, and how many times the stem cells divide. With every division, there’s a risk of a cancer-causing mutation in a daughter cell. Tomasetti and Vogelstein reasoned that the tissues that host the greatest number of stem cell divisions are those most vulnerable to cancer. When Tomasetti crunched the numbers and compared them with actual cancer statistics, he concluded that this theory explained two-thirds of all cancers.

George Dvorsky unpacks the findings:

Take colon cancer, for example, which is far more common than cancer of the duodenum. The researchers found that there are about about 1012 stem cell divisions in the colon over a lifetime, compared with 1010 in the duodenum. This would explain why certain tissue types give rise to cancers millions of times more often that other tissue types. As the researchers note in their paper, “[The] lifetime risk of cancers of many different types is strongly correlated (0.81) with the total number of divisions of the normal self-renewing cells maintaining that tissue’s homeostasis.”

In all, the researchers found that 65% of cancer incidence can be attributed to random mutations in genes that drive cancer growth.

But Annalisa Merelli doesn’t want us to think of cancer as simply about luck:

Notably, some types of tissues associated with cancer that are often linked to lifestyle habits—skin and lung, for instance—did show an increase in mutation as a consequence of environmental factors (essentially confirming that quitting smoking and avoiding excessive sun exposure are very good ideas). Further, the study didn’t include two of the most common cancers, breast and prostate. Tomasetti himself had this to say:

“I’m not claiming any cancers, overall across the population, are the result of pure chance,” Tomasetti told the BBC. “But what I am claiming is there are some tissues—for example blood cancer—where there is very little evidence of any hereditary or environmental factor.”

Tara Culp-Ressler adds more context:

“If two-thirds of cancer incidence across tissues is explained by random DNA mutations that occur when stem cells divide, then changing our lifestyle and habits will be a huge help in preventing certain cancers, but this may not be as effective for a variety of others,” Cristian Tomasetti, an assistant professor of oncology at Johns Hopkins and one of the co-authors of the study, told BBC News. “We should focus more resources on finding ways to detect such cancers at early, curable stages.”

As Tomasetti alludes to, the findings don’t mean that doctors should stop encouraging lifestyle changes that can help lower Americans’ risk of developing cancer. Certainly, some cancers are greatly influenced by individual choices.