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: Childhood cancer five-year survivors diagnosed during 1970-1986 in the Childhood Cancer Survivor Study Exposure: Underweight status, defined as body mass index (BMI) < 18.5 kg/m2 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/m2. 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 smok