DNA Errors Responsible for Most Cancer Mutations

There are obviously habits you can practice to lower your risk for getting cancer – but a new study finds that DNA copying "mistakes" are responsible for almost two-thirds of cancer mutations.

The study, published in Science, follows a 2015 report from the same authors Cristian Tomasetti and Dr. Bert Vogelstein that said cancer risk mostly has to do with random DNA mistakes, reports CNN. They noted DNA copying errors could be behind why certain cancers are more common than others (i.e. colon over brain). The new study delves deeper into discussing this "dumb luck," as CNN put it, and its importance over genetic or lifestyle elements related to cancer development.

"It is well-known that we must avoid environmental factors such as smoking to decrease our risk of getting cancer. But it is not as well-known that each time a normal cell divides and copies its DNA to produce two new cells, it makes multiple mistakes," Tomasetti, who is an assistant professor of biostatistics at the Johns Hopkins Kimmel Cancer Center and the Johns Hopkins Bloomberg School of Public Health, said in a statement.

Researchers examined the mutations responsible for abnormal cell growth across 32 cancers and created a mathematical model based on DNA sequencing data from The Cancer Genome Atlas and epidemiologic data from the Cancer Research UK database.

Overall, the Washington Post reports, the analysis found, 66 percent of mutations that contribute to cancer are due to unavoidable DNA-replication mistakes, while 29 percent are attributable to environmental factors and 5 percent to heredity. But it can take three, four or more mutations to make a cell turn malignant, the Post reported, so this is not to say that two-thirds of cancer cases are caused by random copying errors, the researchers said.

Nor is this to say that such random errors caused the most mutations of all cancers. For example, 65 percent of lung cancer mutations are related to environmental elements like smoking and DNA copying errors are responsible for just 35 percent.

"We hope this research offers comfort to the literally millions of patients who have developed cancer but have led near perfect lifestyles," Vogelstein told CNN.

The 2015 study led to debate in the science community since it focused on cancer cases only in the U.S. and didn't look at breast or prostate cancers. The new study showed a comparable pattern around the globe and examined stem cell division data alongside cancer incidence data from the International Agency for Research on Cancer, database amounting to 4.8 billion people. Researchers found a strong correlation with cancer incidence and normal cell divisions in 17 cancer types. They also looked at breast and prostate cancer data.

"I was concerned about the last article, because it didn't talk enough about prevention and it left people thinking, 'Gee you're just destined to get cancer and you can't do anything about it,'" Dr. Otis Brawley, chief medical officer of the American Cancer Society, told CNN. Although "much happier" with the new study, it "doesn't tell me anything I hadn't known for the last 20 years," he added.