It’s long been known that obesity is linked to increased risk of developing colon cancer, but now researchers at the Mayo Clinic campus in Minnesota have found that obesity is associated with worse outcomes in patients who have already been diagnosed and treated for the cancer.
“There was a stronger relationship between BMI and clinical outcome in men compared to women”
The authors found that obesity was significantly associated with a greater number of tumor-containing regional lymph nodes and worse survival rates, independent of other tumor features. Their data also showed that depending on a patient’s gender, varying levels of obesity were associated with an increased risk of death ranging from 19 percent to 35 percent, compared to non-obese patients. The study was published today in Clinical Cancer Research.
The researchers say their findings, culled from thousands of patients who had their colon cancer surgically removed and were enrolled in one of seven chemotherapy trials supported by the National Cancer Institute (NCI), suggest that colon cancer patients should try to maintain a body mass index (BMI) that is less than 30. A BMI less than 30 can fall into normal (20–24.9) or overweight (25–29.9) categories. A BMI 30 and higher is considered obese. A person’s BMI is the ratio between height and weight, and can be calculated at www.nhlbisupport.com/bmi.
“We found that obesity is associated with more aggressive colon cancers, with the effect being stronger in men than in women,” says the study’s lead author, Frank Sinicrope, M.D., a Mayo Clinic medical oncologist. “Our data suggest that a little extra weight is okay, but body weight in the obesity range puts a patient at increased risk for cancer recurrence and spread and, based upon other studies, also would be expected to increase the risk of precancerous colon polyps and a second colon cancer.”
The study population included patients participating in clinical trials conducted by Mayo Clinic and the North Central Cancer Treatment Group and a study from the Southwest Oncology Group. The researchers calculated BMI at study entry in 4,381 patients with resected stage II (lymph node negative) or stage III (node positive) colon cancers who had enrolled in one of seven randomized trials testing 5-fluorouracil-based adjuvant chemotherapy. Among these patients, 868 (20 percent) were considered obese. Within this group, 606 patients were class 1 (BMI 30–34.9) and 262 were very obese (class 2 or 3, which is a BMI of 35 or greater).
Researchers found that, overall, class 2 and 3 obesity was associated with a 19 percent increase in the risk of death, and that any class of obesity was significantly associated with an increased number of metastatic regional lymph nodes, compared to normal weight patients.
The researchers also observed differences between men and women. “There was a stronger relationship between BMI and clinical outcome in men compared to women,” says Dr. Sinicrope. “The greater the level of obesity in men, the higher their risk of cancer recurrence and death. In women, however, the highest risk was seen in those with class 1 obesity, compared to normal weight women.”