Purpose

To study the relationship between body mass index (BMI) and rates of sphincter-preserving operations, overall survival, cancer recurrence, and treatment-related toxicities in patients with rectal cancer.

Patients and methods

We evaluated a nested cohort of 1,688 patients with stage II and III rectal cancer participating in a randomized trial of postoperative fluorouracil-based chemotherapy and radiation therapy.

Results

Obese patients were more likely to undergo an abdominoperineal resection (APR) than normal-weight patients (odds ratio, 1.77; 95% CI, 1.27 to 2.46). When analyzed by sex, increasing adiposity in men was a strong predictor of having an APR (P <.0001). Obese men with rectal cancer were also more likely than normal-weight men to have a local recurrence (hazard ratio [HR], 1.61; 95% CI, 1.00 to 2.59). In contrast, obesity was not predictive of cancer recurrence in women, nor was BMI predictive of overall mortality in either men or women. Underweight patients had an increased risk of death (HR, 1.43; 95% CI, 1.08 to 1.89) compared with normal-weight patients but no increase in cancer recurrences. Among all study participants, obese patients had a significantly lower rate of grade 3 to 4 leukopenia, neutropenia, and stomatitis and a lower rate of any grade 3 or worse toxicity when compared with normal-weight individuals.

Conclusion

Increasing BMI in male patients with rectal cancer is associated with a decreased likelihood of sphincter preservation and a higher chance of local recurrence. For both men and women, overweight and obese patients experience less toxicity associated with adjuvant chemoradiotherapy, suggesting that actual body weight dosing of fluorouracil for obese patients is justified.