A huge new study published on Thursday is making a big claim about cancer and the patients who suffer from it: it may be a matter of bad luck instead of bad genes. The study claims that most mutations that lead to cancer just crop up out of the blue, and naturally, rather than due to adverse actions like smoking or bad genes.

While it is true that those things also contribute to cancer rates, bad luck plays a much bigger role than scientists realized, indicating that many cases of cancer are unavoidable. Scientists estimate that about 40 percent of cancers are preventable based on research, and have been trying to figure out what causes the other cancers that aren’t known ot be preventable.

The reality is that when a normal cell divides, it makes a few mistakes when it copies the DNA, which is totally natural. Usually, these mutations are to pieces of the DNA that aren’t important, but every now and then they occur in a cancer driver gene, which scienitsts now attribute to luck.

The abstract of the paper states: “Most textbooks attribute cancer-causing mutations to two major sources: inherited and environmental factors. A recent study highlighted the prominent role in cancer of replicative (R) mutations that arise from a third source: unavoidable errors associated with DNA replication. Tomasetti et al. developed a method for determining the proportions of cancer-causing mutations that result from inherited, environmental, and replicative factors (see the Perspective by Nowak and Waclaw). They found that a substantial fraction of cancer driver gene mutations are indeed due to replicative factors. The results are consistent with epidemiological estimates of the fraction of preventable cancers.”