The Obesity/Cancer Connection: Evidence Grows, More Calls for Action

Published in June 2015 Issue             

A new study in the April 16 online issue of
JAMA Oncology finds obesity was associated with an increased risk for prostate cancer in African American men and that the risk quadrupled as body-mass index (BMI) increased.

During a median follow-up of 5.6 years, 1,723 men developed prostate cancer (270 total cases among African American men and 1,453 total cases among non-Hispanic white men). Overall, the study found a 58 percent increased risk for prostate cancer among African American men.

Obesity was not associated with risk for prostate cancer overall among non-Hispanic white men but there was a significant association between obesity and the risk for prostate cancer in African American men. The risk increased across BMI categories, jumping from 28 percent among African American men with a BMI less than 25 to 103 percent among African American men with a BMI of at least 35, according to the results.

Study authors noted the reasons underlying their findings are unknown but they speculate that one explanation may be that the biological effects of obesity differ in African American and non-Hispanic white men.

"This study reinforces the importance of obesity prevention and treatment among African American men, for whom the health benefits may be comparatively large. Although obesity is linked to poor health outcomes in all populations, clinicians might consider the unique contribution of obesity prevention and treatment to the health of their AA [African American] patients. Such targeted efforts may contribute to reductions in prostate cancer disparities," the article concludes.

Researchers analyzed data collected between 2001 and 2011 by the Selenium and Vitamin E Cancer Prevention Trial, which included nearly 3,400 black men and almost 22,700 white men, all cancer-free and age 55 and up at the start.

In an editor's note, Charles R. Thomas Jr., MD, a deputy editor of JAMA Oncology, wrote: “Despite the limitations inherent in the methodology utilized for the analysis and the inability to define a clear mechanism behind the association between BMI and risk, the findings do provide a further rationale for weight reduction and a target BMI for clinicians to aim for in care of African American men."

The obesity/cancer connection is not new. Last year, the American Society of Clinical Oncology (ASCO) “called for increased education, research and advocacy to reduce the toll of obesity, both as a leading cause of cancer and a complication in the care of cancer patients.”

This was ASCO’s first-ever policy statement on cancer and obesity. In it the organization emphasized that obesity is becoming a central challenge in cancer prevention and care, and that it is projected to soon overtake tobacco as the leading preventable cause of cancer in the United States. The complete statement, which was published online in the October 1, 2014 edition of the Journal of Clinical Oncology is available online here.

ASCO reports that by 2030, almost 500,000 Americans may be diagnosed with obesity-related cancers annually and that among people with cancer, obesity can increase the risk of cancer recurrence and lower survival. They refer to a 2003 study in the New England Journal of Medicine that suggests that being overweight or obese contributes to as many as one in five cancer-related deaths.

“With nearly three in four Americans obese or overweight, obesity has become a tremendous public health challenge that also impacts cancer care and prevention today,” said ASCO Immediate Past President Dr. Clifford A. Hudis, MD, FACP, at the time the policy statement was issued. “Cancer doctors need to play a lead role in reducing obesity’s impact, both in the care of our patients and as advocates for broader action. We can’t allow obesity to undo decades of progress in prevention, early diagnosis and treatment of cancer.”

Obesity is a known risk factor for colon, breast, endometrial, kidney and esophageal cancers.

Bariatric Surgery and Cancer Prevention

The benefits of weight loss and bariatric surgery have also been well documented. In 2009, a study in Lancet Oncology found that women with obesity who undergo bariatric surgery experience a 42 percent drop in their cancer risk.

Nicolas Christou

Dr. Nicolas Christou, the director of bariatric surgery and professor of surgery at McGill University in Montreal conducted a study back in 2008 that showed men and women who had bariatric surgery were 78 percent less likely to develop any cancer, when compared with their equally overweight counterparts who did not have surgery. The study findings were first reported at the ASMBS Annual Meeting and later published in SOARD.

“The study was significant because it was the first time that bariatric surgery was shown to have such an affect on the incidence of several specific types of cancer, particularly breast and colon cancers,” said John M. Morton, MD, ASMBS President and Director of Bariatric Surgery at Stanford Hospital & Clinics.

The incidence of breast and colon cancer was reduced by 85 percent and 70 percent, respectively. Researchers also observed a 70 percent reduction in pancreatic cancer and a 15 percent reduction in uterine cancer, but there were not enough cases of these particular cancers to be statistically significant.

A study published in the journal, Obesity, in 2009 showed bariatric surgery resulted in significant decreases in the incidence of cancer and cancer-related deaths, primarily among patients with advanced cancers. The Swedish Obese Subjects (SOS) study of 2,000 patients, published in Lancet Oncology in 2009, compared outcomes of those who went on diet programs and those that had bariatric surgery and found a dramatic reduction in cancer incidence among women who had surgery.

“The evidence is there and now more physicians, policy makers and organizations are paying attention,” said Dr. Morton. “We must support evidence-based treatments for obesity. It’s a matter of life and death.”