By Amir Khan
Obesity and physical inactivity are linked to an increased risk of colorectal cancer, according to a study published today in the journal Cancer Research — but more research is needed before scientists can say whether, or for whom, losing weight and exercising more will actually reduce cancer rates.
Study subjects with higher body mass who exercised less were more likely than others to develop colorectal cancer — but only among those with a particular subtype of the cancer, a finding that may one day permit doctors to develop treatments that are tuned to the particular subtype or patient.
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“We know that exercise and avoiding obesity decrease colorectal cancer risk, but little is known about why," Shuji Ogino, M.D., Ph.D., associate professor of pathology at Dana-Farber Cancer, said in a statement. To get at the "why", Ogino and his colleagues measured the presence or absence of a particular molecule — named CTNNB1 — that was present in some tumors, that is associated with obesity and that, when it mutates, has been found to cause colorectal, ovarian and other types of cancer.
Fifty four percent of study subjects had tumors where the molecule was not present. The colorectal cancer risk among these "CTNNB1-negative" patients increased by more than a third for every 10 pounds more they weighed. Those who exercised less saw a statistically significant increase in their cancer risk, as well.
On the other hand, neither weight gain nor decreased exercise levels increased the cancer risks of study subjects whose tumors contained the CTNNB1 molecule.
Approximately 1,140,000 people in America diagnosed with colorectal cancer, according to the American Cancer Society. Researchers say the latest findings are an indication that doctors may need to treat the cancer as two, if not more, separate diseases.
“Typically colon cancer is treated as a single disease," Ogino said in a statement. "We need to integrate molecular pathology and epidemiology in education and research to improve public health."
Peter Campbell, PhD, director of the tumor repository for the American Cancer Society, says that treatment for colorectal cancer should be tailored to the patient, and that studies such as this are paving the way for individualized therapies.
“No two patients have a similar tumor if you compare them on a molecular basis,” he says. “Studies like this are really starting to get towards patient-centered medicine, where we’re beginning to understand that medicine isn’t one size fits all.”
The findings may also one day help people predisposed to CTNNB1-negative cancer avoid the disease entirely.
“In the future, we may be able to identify individuals who are susceptible to the development of CTNNB1-negative tumors, and lifestyle preventive measures can be taken,” the researchers wrote in the study. “Thus, our findings may help us develop better cancer prevention strategies.”
However, until technology is able to determine what kind of colorectal cancer you may be at risk for, it’s important to exercise and eat right to reduce your risk of developing the disease, Campbell says.
“Age appropriate screening starting at age 50 is the biggest bang for your buck,” he says. “Eating a diet high in fruits and vegetables and low in red meat is also very important. Colorectal cancer is the largest cause of nonsmoking cancer in the United States, but it doesn’t have to be.”
"Obesity and Lack of Exercise May Raise Risk For Colorectal Cancer" originally appeared on Everyday Health.