Abstract IA39: Explaining the obesity paradox in cancer: The role of muscle

Abstract

Abstract Although overweight and obesity, assessed by body mass index (BMI), are reliably related to an increased risk of cancer, data on the relationship between BMI and cancer prognosis are inconsistent. An emerging literature suggests that the relationship between BMI and cancer survival is often U-shaped and that overweight, and in some cases mild obesity, may not increase risk and might even offer protection. This is termed the “obesity paradox” and has been demonstrated in patients with lymphoma, leukemia, colorectal, endometrial, thyroid, and renal cancers. Reasons provided to explain the obesity paradox in cancer include methodologic biases such as reverse causality, confounding, detection bias, or collider bias. Yet others posit that the association reflects true benefits of a higher BMI, including extra nutritional reserves, greater muscle mass, a lower likelihood of dose-limiting toxicity, and less aggressive tumors, each of which may be independently associated with better prognosis. We will present evidence of the obesity paradox in breast and colorectal cancer. We will also present data on the importance of adequate muscle reserves to optimal cancer outcomes and explain how muscle may explain the U-shaped relationship between BMI and survival in these cancers. We will show that BMI is not an accurate measure of either adiposity or muscle, especially among cancer survivors. We will illustrate that when BMI is used to measure body size, an obesity paradox can emerge because “overweight” patients often have higher levels of protective muscle but lack adiposity levels sufficient to increase their risk of mortality. Citation Format: Bette Caan. Explaining the obesity paradox in cancer: The role of muscle [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr IA39.