Risk of increased mortality in underweight survivors: A brief report from the Childhood Cancer Survivor Study

Background: Approximately 1 in 10 adult survivors of childhood cancer is underweight. Although the consequences of being overweight or obese have been well described, outcomes among childhood cancer survivors who are underweight are unknown. Objective: To determine whether underweight status increases the risk of mortality. Procedure: Cohort study: Marginal models with generalized estimating equations to evaluate the associations between body mass index (BMI), serious or life-threatening chronic conditions, and death in the setting of long-term follow-up questionnaires and National Death Index search. Participants: C. Exposure: Underweight status, defined as body mass index (BMI) < 18.5 kg/m(2) compared with ideal body weight. Based on available literature on body weight and mortality from the general population, ideal body weight was defined as BMI 22.0-24.9 kg/m(2). Main outcomes: Overall mortality and cancer-specific mortality. Results: Of 9454 survivors (median age 35 years old (range, 17-58), an average of 17.5 years from diagnosis), 627 (6.6%) participants were underweight at baseline or follow-up questionnaire. Of 184 deaths, 29 were among underweight survivors. Underweight status was more common among females (9.1% vs. 4.5%, p < .01) and participants with younger age at diagnosis (8.2% for < 5 years vs. 6.1% for >= 5 years, p < .01), lower household income (8.9% for < $20,000 vs. 6.0% for >= $20,000, p < .01), or a history of serious chronic condition (p = .05). After adjustment for these factors, in addition to prior smoking and a history of radiation therapy, the risk of all-cause mortality within two years of BMI report was increased (OR 2.85; 95% CI: 1.63-4.97; p < .01) for underweight survivors, compared with ideal-weight survivors. Conclusions: Childhood cancer survivors who are underweight are at increased risk for late mortality that appears unrelated to smoking status, recognized chronic disease, or subsequent malignancy. Whether targeted nutritional interventions would ameliorate this risk is unknown.