Increased Prediagnosis BMI Associated With Increased Risk of Second Obesity-Associated Cancers in Colorectal Cancer Survivors


Key Points

  • Baseline overweight and obesity were associated with 39% and 47% increased risks of second obesity-associated cancers.
  • The increase in risk for first obesity-associated cancers was 18% for overweight and 61% for obesity at baseline.

Overweight and obesity are associated with increased risk of primary colorectal cancer, as well as increased risk of breast, endometrial, esophageal, pancreatic, and kidney cancers. In a pooled analysis of prospective cohort studies reported in the Journal of Clinical Oncology, Gibson et al found that prediagnosis overweight or obesity was associated with increased risk of second obesity-related cancers in colorectal cancer survivors.

Study Details

The study involved 11,598 incident first primary colorectal cancer survivors from five prospective cohort studies (National Institutes of Health-AARP Diet and Health Study; Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial; Iowa Women’s Health Study; Alpha-Tocopheral, Beta-Carotene Cancer Prevention Study; and Agricultural Health Study). Among all colorectal cancer survivors, 44% had body mass index (BMI) of 25 to 29.9 kg/m2 (overweight) and 25% had BMI of ≥ 30 kg/m2 (obesity) at baseline. Second obesity-associated cancers were defined as postmenopausal breast, kidney, pancreas, esophageal adenocarcinoma, and endometrial cancers.

Increased Risk of Second Cancers

During 128,383 person-years of follow-up after colorectal cancer diagnosis and a median follow-up of  3.7 years, 224 obesity-associated second cancers were diagnosed (118 postmenopausal breast, 43 kidney, 34 pancreas, 10 esophageal adenocarcinoma, and 19 endometrial cancers).

Compared with survivors with prediagnosis BMI of 18.5 to 24.9 kg/m2, risk of a second obesity-associated cancer was significantly increased in those who were overweight (hazard ratio [HR] = 1.39; 95% confidence interval [CI] = 1.01–1.92) and in those who were obese (HR = 1.47, 95% CI = 1.02–2.12; P = .03 for trend). An increase of 5 BMI units at baseline was associated with a nonsignificant 12% increased risk of second cancer (HR = 1.12, 95% CI = 0.98–1.29). 

Although hazard ratios were generally elevated for each category of second cancer among overweight and obese patients, the increased risks were not statistically significant. For postmenopausal breast cancer, the most common second cancer, hazard ratios were 1.36 (95% CI = 0.89–2.08) for overweight and 1.17 (95% CI = 0.71–1.93) for obesity.

Increased Risk of First Cancers

In comparison, among the 25,364 participants in the pooled cohorts (15,074 with breast, 3,440 with kidney, 2,929 with pancreas, 931 with esophageal, and 2,990 with endometrial cancers), hazard ratios for first obesity-associated cancers were 1.18 (95% CI = 1.14–1.21) for overweight and 1.61 (95% CI = 1.56–1.66) for obesity at baseline (P < .001 for trend; HR = 1.23, 95% CI = 1.21–1.24 per 5 BMI units). Colorectal cancer survivors were somewhat more likely than the overall cohort to be overweight (44% vs 41%) and obese (25% vs 21%) prior to diagnosis.

The investigators concluded: “[Colorectal cancer] survivors who were overweight or obese before diagnosis had increased risk of second obesity-associated cancers compared with survivors with normal weight. The risks were similar in magnitude to those observed for first cancers in this population, suggesting increased prevalence of overweight or obesity, rather than increased susceptibility, may contribute to elevated second cancer risks in colorectal cancer survivors compared with the general population. These results support emphasis of existing weight guidelines for this high-risk group.”

Todd M. Gibson, PhD, of St. Jude Children’s Research Hospital, is the corresponding author for the Journal of Clinical Oncology article.

The study was supported by the National Cancer Institute. The study authors reported no potential conflicts of interest.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.