Impact of obesity on cancer survivorship and the potential relevance of race and ethnicity

Abstract

Evidence that obesity is associated with cancer incidence and mortality is compelling. By contrast, the role of obesity in cancer survival is less well understood. There is inconsistent support for the role of obesity in breast cancer survival, and evidence for other tumor sites is scant. The variability in findings may be due in part to comorbidities associated with obesity itself rather than with cancer, but it is also possible that obesity creates a physiological setting that meaningfully alters cancer treatment efficacy. In addition, the effects of obesity at diagnosis may be distinct from the effects of weight change after diagnosis. Obesity and related comorbid conditions may also increase risk for common adverse treatment effects, including breast cancer-related lymphedema, fatigue, poor health-related quality of life, and worse functional health. Racial and ethnic groups with worse cancer survival outcomes are also the groups for whom obesity and related comorbidities are more prevalent, but findings from the few studies that have addressed these complexities are inconsistent. We outline a broad theoretical framework for future research to clarify the specifics of the biological-social-environmental feedback loop for the combined and independent contributions of race, comorbid conditions, and obesity on cancer survival and adverse treatment effects. If upstream issues related to comorbidities, race, and ethnicity partly explain the purported link between obesity and cancer survival outcomes, these factors should be among those on which interventions are focused to reduce the burden of cancer.

Figure 1.

Framework for the combined influence of race and obesity on cancer survivorship. The bottom Venn diagram represents distal determinants of disparate cancer survival outcomes. Disparities in these underlying social and physical determinants are embodied and expressed through biological responses and genetic pathways, which lead to disparities in risk for obesity and comorbidities. In the top Venn diagram, differential genes, obesity, and comorbidities then lead more proximally to disparities in survivorship outcomes. All of these relationships operate in a feedback loop of biological–social–physical environment interactions, making it difficult to disentangle which of the underlying or mediating factors are the greatest contributors to disparities in survivorship.