Though genetic and lifestyle factors can play a significant role in the development of certain cancers, a new study has found that bad luck in mutating stem cells is the biggest risk factor for 2/3 of all cancers overall. The work was performed by Cristian Tomasetti and Bert Vogelstein of Johns Hopkins University School of Medicine and Johns Hopkins Kimmel Cancer Center, respectively. The paper was published in Science.
“All cancers are caused by a combination of bad luck, the environment and heredity, and we’ve created a model that may help quantify how much of these three factors contribute to cancer development,” Vogelstein said in a press release. “Cancer-free longevity in people exposed to cancer-causing agents, such as tobacco, is often attributed to their ‘good genes,’ but the truth is that most of them simply had good luck."
This development has some rather striking implications. Improving certain lifestyle factors like weight, tobacco use, or alcohol consumption can certainly contribute to the prevention of some specific cancers, such as lung cancer. However, for other cancers that are more likely to be influenced by unpredictable cell mutations, the lifestyle choices might not make that much of a difference. This could warrant the need to more aggressively pursue ways to identify cancer in the earliest stages, when it can more easily be dealt with.
In order to determine how random mutations influenced the risk of developing cancer, Tomasetti and Vogelstein searched existing studies that quantified the number of cell divisions that stem cells undergo over the course of a lifetime in over 30 different types of tissue. They found a correlation between the total number of times a stem cell will divide in a tissue with the likelihood that the tissue will develop cancer.
This is likely due to the fact that the more times DNA is replicated for cell division, the more likely it becomes that there will be an error and mutations will occur. If the mutation is not edited properly, it will remain in the sequence, adding to other mutations that could be acquired in the future. If this continues, it can lead to cancer. This is the first study to examine the odds of this occurrence quantitatively.
“We found that the types of cancer that had higher risk than predicted by the number of stem cell divisions were precisely the ones you’d expect, including lung cancer, which is linked to smoking; skin cancer, linked to sun exposure; and forms of cancers associated with hereditary syndromes,” says Vogelstein.
Unfortunately, this study does not include some cancers, such as breast cancer and prostate cancer, as previous studies quantifying the number of mutations have not been consistent. This could be clarified by future research. Additionally, the study isn't saying that lifestyle factors aren't important and shouldn't be cause for concern in the prevention of cancer.
“This study shows that you can add to your risk of getting cancers by smoking or other poor lifestyle factors. However, many forms of cancer are due largely to the bad luck of acquiring a mutation in a cancer driver gene regardless of lifestyle and heredity factors. The best way to eradicate these cancers will be through early detection, when they are still curable by surgery,” concludes Vogelstein.