Obesity and Cancer Treatment Outcomes: Interpreting the Complex Evidence

Area of Science:

• Oncology
• Epidemiology
• Metabolic Health

Background:

• Epidemiological data and biological mechanisms suggest a link between excess adiposity (body mass index, BMI) and cancer risk.
• Interpreting the influence of overweight (BMI 25.0-29.9 kg/m² ) or obesity (BMI ≥ 30.0 kg/m²) on cancer progression, mortality, and survival presents significant challenges.

Purpose of the Study:

• To explore the complex relationship between elevated BMI and cancer outcomes, including disease progression, treatment, and survival.
• To critically evaluate methodological challenges in interpreting the impact of obesity on cancer, such as selection bias, confounding, and reverse causality.

Main Methods:

• Review of epidemiological evidence and biological plausibility for the link between adiposity and cancer.
• Discussion of methodological issues in cancer research concerning patients with elevated BMI, including treatment selection and surgical outcomes.
• Framework for evaluating biases and confounding factors in studies investigating obesity and cancer outcomes.

Main Results:

• Elevated BMI can influence treatment decisions (surgery, chemotherapy dosing, clinical trial eligibility) and may complicate surgical outcomes (morbidity, lymph node harvest, margins).
• Suboptimal chemotherapy dosing in obese patients might negatively affect prognosis, while immune checkpoint inhibitor efficacy could be enhanced, though reverse causality is a concern.
• The 'obesity paradox' describes instances where overweight or obesity is paradoxically associated with improved survival.

Conclusions:

• The direct versus indirect effects of overweight and obesity on cancer outcomes remain a critical research question.
• Methodological rigor, particularly prospective studies, is essential to accurately interpret causality and avoid spurious conclusions in obesity-cancer research.
• Addressing biases like selection bias, confounding, and reverse causality is crucial for a clearer understanding of the obesity-cancer relationship.