Obesity paradox in patients with cancer: A systematic review and meta-analysis of 6,320,365 patients

BACKGROUND. Obesity, defined as a body mass index (BMI) [≥] 30 kg/m2, is associated with a significant increase in risk of many cancers. In last years, various studies suggested that obese cancer patients have better outcomes than non obese patients. This phenomenon, also known as the obesity paradox, is not well understood and presents controversial explanations. We performed a systematic review and metaanalysis to assess the association between obesity and outcome after a diagnosis of cancer. PATIENTS AND METHODS. PubMed, the Cochrane Library, and EMBASE were searched from inception to January 2020, for studies reporting prognosis of patients with obesity and cancer. Risk of death, cancer specific survival (CSS) and progression were pooled to provide an adjusted hazard ratio with a 95% confidence interval (HR 95%CI). The primary outcome of the study refers to overall survival (OS) in obese vs non obese patients with malignancies. Secondary endpoints were CSS and progression or disease free survival (PFS or RFS). RESULTS. Mortality and relapse associated with obesity in patients with cancer were evaluated among n=6,320,365 participants (n=203 studies). Overall, association of obesity and cancer was associated with a reduced OS (HR =1.14, 95% CI: 1.09 1.19; P<.01) and CSS (HR=1.17, 95%CI 1.12 1.23; P<.01). Patients were also at increased risk for relapse (HR=1.13, 95%CI 1.07 1.19; P<.01). Patients with breast, colorectal and uterine tumors were at increased risk of death. Conversely, obese with lung cancer, renal cell carcinoma and melanoma survived longer that non obese. CONCLUSIONS. In many cancer patients, obesity reduces survival and increases the risk of relapse. In lung cancer, renal cell carcinoma and melanoma obesity was protective in terms of outcome. More intensive follow up, adequate dosing of oncological treatments, calories intake restrictions, physical activity and monitoring of obesity related complications are effective measures for reducing mortality in these subjects.