A pair of new studies from the American Cancer Society explore the relationship of colorectal cancer survival to two potential risk factors: obesity and diabetes. Together the studies, which appear in the Journal of Clinical Oncology, reveal new clues to the disease.
The impact of body mass index (BMI) on survival after colorectal cancer diagnosis is not well understood. For the first study, lead author Peter Campbell compared BMI before and after a diagnosis of colorectal cancer and survival among more than 2,000 men and women participating in the Cancer Prevention Study-II. The analysis found being obese before diagnosis was associated with 30 percent higher risk of mortality resulting from all causes (relative risk [RR], 1.30; 95% CI, 1.06 to 1.58), a 35 percent higher increase of death from colorectal cancer (RR, 1.35; 95% CI, 1.01 to 1.80), and a 68 percent higher risk of death from cardiovascular disease (RR, 1.68; 95% CI, 1.07 to 2.65). Meanwhile, being obese after diagnosis was not associated with all-cause or cause-specific mortality. The authors conclude that prediagnosis BMI, but not postdiagnosis BMI, is an important predictor of survival among patients with nonmetastatic colorectal cancer.
The second study, also led by Dr. Campbell, looked at diabetes. The authors wanted to know whether type 2 diabetes mellitus was associated with poorer survival among patients with colorectal cancer and also to find out whether that association varies by sex, insulin treatment, how long patients had diabetes, and how long they were using insulin. The analyzed outcomes among 2,278 men and women diagnosed with nonmetastatic colon or rectal cancer in the Cancer Prevention Study-II. They found among men and women combined, colorectal cancer patients with type 2 diabetes mellitus were at higher risk of death from any cause (RR, 1.53; 95% CI, 1.28 to 1.83), from colorectal cancer (RR, 1.29; 95% CI, 0.98 to 1.70), and from cardiovascular disease (RR, 2.16; 95% CI, 1.44 to 3.24). They did not find any differences by sex, how long patients had diabetes, or how long they had been using insulin use. They conclude patients with colorectal cancer and type 2 diabetes have a higher risk of mortality than patients with CRC who do not, with a particularly higher risk of death from cardiovascular disease.
We asked Dr. Campbell what he drew from the studies.
“I think the most important findings from these papers were that two very common metabolic conditions, obesity and type 2 diabetes, that usually developed several years prior to cancer diagnosis had such negative impacts on survival after colorectal cancer diagnosis. To me, I think these results really underscore, among other things, the importance of maintaining a healthy body weight throughout life.”