A new study found that, more than bad luck, nine out of 10 cancers are caused by environmental and lifestyle risk factors.
Cancer is a result of DNA cell mutations, which lead to the aberrant growth of cells. The disease process is complicated and, for study author Dr. Yusuf Hannun of the Stony Brook University Cancer Center, the scientific community must come together to establish models that can help identify the extrinsic and intrinsic factors that cause the particular types of the disease.
In January 2015, researchers from Johns Hopkins University said in a study that most of the tissue differences associated with cancer risk are caused by nothing but bad luck. The study conclusion, however, garnered numerous negative feedback.
"Many scientists argued against the 'bad luck' or 'random mutation' theory of cancer but provided no alternative analysis to quantify the contribution of external risk factors," said Song Wu, lead author of the new research and an assistant professor in the applied mathematics and statistics department in Stony Brook.
The research team then embarked on a study using the same data that the previous study used. This time, the paper gives an alternative examination of the issue by using four different analytic methods.
First, the team studied the extrinsic risks by tissue cell turnover. They specifically reanalyzed the quantitative relationship between the apparent lifetime risk of cancer and the separation of normal tissue stem cells among the cancer types. Having a directly proportional relationship signifies that intrinsic risk factors have a significant role in disease development.
The verdict? The relationship pattern is rare and only about 10 percent of cancers are influenced by intrinsic factors. Such finding is backed up by epidemiologic data showing that people who migrated to other countries developed the cancer prevalent in the area where they moved to.
Next, the researchers performed a mathematical survey and studied the "fingerprints" embedded on cancer genomes by various mutation processes. After identifying the signatures, they categorized each as having either an intrinsic or extrinsic root.
The team found that while a few types of cancer are caused by more than 50 percent of intrinsic mutations, most cancers are likely due to extrinsic factors.
In the third method, the experts studied the SEER (Surveillance, Epidemiologic and End Results Program) data. They discovered that the incidence and mortality rates of cancer continue to rise, signifying that extrinsic factors are strongly involved.
For the last approach, the team utilized computational designing to delve into the roles of intrinsic mechanisms to cancer development based on gene mutations.
The researchers found that more than three mutations are needed in order for cancer to develop. Intrinsic factors are inadequate to be responsible for the observed risks, implicating the small rates of intrinsic cancer risks in most cancers.
"Collectively, we conclude that cancer risk is heavily influenced by extrinsic factors," the authors wrote. "These results are important for strategizing cancer prevention, research and public health."
The study was published in the journal Nature.
