cancer
March 24, 2017

Two-thirds of cancers are caused by bad luck

Cancer is brought on by errors in genetic material, and two-third of all cancer-causing errors come from arbitrary mistakes, not as a result of heredity or ecological factors, according to a new report in the journal Science.

The errors, or mutations, cause cancer because even a small error in genetic material can make cells grow out of control, the study said.

Past research has shown two big factors play a role in the generation of cancer-causing mutations: Either the mutation was passed down, or it was brought on by external factors that harm DNA, like cigarette smoke or radioactivity.

However, cancer can also arise from arbitrary errors. When a cell divides to reproduce, it duplicates its DNA so that each one of the new cells will have its own copy of the genetic code. However, every time this copying occurs, there is a chance for a mistake to happen. In many cases, these errors can lead to cancer.

"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," study author Cristian Tomasetti, assistant professor of biostatistics at the Johns Hopkins Kimmel Cancer Center, said in a statement. "These copying mistakes are a potent source of cancer mutations that historically have been scientifically undervalued, and this new work provides the first estimate of the fraction of mutations caused by these mistakes."

Looking at Cancerous Mutations

To reach their conclusion, the researchers looked at the mutations that cause abnormal cell growth in 32 cancer types. Then, the created a mathematical model using DNA sequencing information from The Cancer Genome Atlas and epidemiologic information from the Cancer Research UK database.

The study team's mathematical model showed the driving forces behind many cancer types. For instance, 77 percent of key mutations in pancreatic cancers are as a result of arbitrary DNA copying errors, 18 percent to environmental factors, like smoking, and the final 5 percent to heredity.

The researchers say their method is similar to efforts to figure out why typos happen when typing a book. They might be due to a bad keyboard (hereditary issues), typing while tired (environmental issues) or random chance.

"You can reduce your chance of typographical errors by making sure you're not drowsy while typing and that your keyboard isn't missing some keys," said study author Dr. Bert Vogelstein, co-director of the Ludwig Center at the Johns Hopkins Kimmel Cancer Center."But typos will still occur because no one can type perfectly. Similarly, mutations will occur, no matter what your environment is, but you can take steps to minimize those mutations by limiting your exposure to hazardous substances and unhealthy lifestyles."

He added that people who develop cancer despite avoiding known risk factors should not feel guilty, based on the study’s findings.

"It's not your fault," Vogelstein said. "Nothing you did or didn't do was responsible for your illness."

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Image credit: Steve Gschmeissner/Science Source