Do you ever find yourself worried about what caused a loved one’s cancer or perhaps your own and want to get to the bottom of whether it might have been physiological or derived from external environmental risks?
New research out this week has shown that 70 to 90 percent of cancers are caused by environmental factors in a frightening turnaround from research tabled earlier in 2015 that pointed to genetic factors.
A team of researchers from Stony Brook University, New York, led by Yusuf Hannun, MD, the Joel Strum Kenny Professor in Cancer Research and Director of the Stony Brook University Cancer Center, have found quantitative evidence proving that extrinsic risk factors, such as environmental exposures and behaviours weigh heavily on the development of a vast majority (approximately 70 to 90 percent) of cancers. The finding, reported in the December 16 online issue of Nature, in a paper titled “Substantial contribution of extrinsic risk factors to cancer development,” may be important for strategising cancer prevention, research and public health.
Inspired by a January 2015 research paper in Science, which concluded that the majority of the variation in cancer risk among tissues is due to “bad luck,” the Stony Brook team used the same data to assess what leads to the risk of developing cancer. And this team of scientists concluded the opposite – that most cancers are the result of external risk factors not because of internal or intrinsic factors of “bad luck”.
The scientists undertaking the study developed four distinct approaches to assess cancer risk. With these four approaches, they discovered collectively and individually that most cancers are attributed largely to external risk factors, with only 10-to-30 percent attributed to random mutations, or intrinsic factors.
As reported in News Medical, firstly, they re-examined the association between lifetime cancer risk for lung, pancreatic and colorectal cancer, as well as cancer of other tissues, and the division of normal tissue stem cells in the individuals reported in the Science paper. Their findings showed that tissue with similar stem cell divisions did not show a similar observed lifetime cancer risk and concluded that intrinsic factors only play an important role in around 10% of cancers.
Then secondly, the team analysed studies on mutational signatures in cancer and identified 30 distinct signatures among various cancers. The signatures were categorized as having either extrinsic or intrinsic origins. The analysis showed that the majority of cancers such as lung, colorectal, bladder and thyroid cancers had large numbers of mutations that were likely caused by extrinsic factors.
Thirdly, the researchers assessed the Surveillance, Epidemiologic and End Results Program data, which showed that the incidence of cancer and cancer mortality have been increasing, suggesting that external factors contribute heavily to these cancers.
Finally, the team used known gene mutations and the likelihood that they arise due to intrinsic mutations rates to perform computational modeling and determine the contribution of intrinsic factors to the development of cancer.
Co-author of the paper Yusuf Hannun says the scientific team’s approach “provides a new framework to quantify the lifetime cancer risks from both intrinsic and extrinsic factors, which will have important consequences for strategising cancer prevention, research and public health.
With all the additional genetic research around, we all worry about whether one day we will be found to have cancer. And for those already confronted by it, the curiosity over its cause is not small.