Trends in Obesity Prevalence Among Patients Enrolled in Clinical Trials for Obesity-Related Cancers, 1986 to 2016

IMPORTANCE: Obesity rates have risen in the United States since the 1980s. Several studies have shown links between obesity and the incidence of specific cancer types, but none have systematically examined obesity prevalence at the time of cancer diagnosis, or among clinical trial participants, all of which may affect clinical outcomes. OBJECTIVE: To examine the prevalence of obesity and, separately, overweight and obesity over 30 years among patients with cancer enrolled in clinical treatment trials for obesity-related cancers; and to compare trends with corresponding trends in the US. DESIGN, SETTING, AND PARTICIPANTS: This cohort study examined clinical treatment trials for obesity-related cancers conducted by the SWOG Cancer Research Network at community and academic sites. Participants included adult patients enrolled in phase 2 or phase 3 clinical treatment trials in obesity-related cancers between 1986 and 2016. Statistical analysis was performed from June 2020 to July 2022. EXPOSURES: Year of enrollment to a clinical trial. MAIN OUTCOMES AND MEASURES: Prevalence of obesity (body mass index [BMI] ≥ 30) and overweight or obesity (BMI > 25) at the time of clinical trial enrollment. Multivariable logistic regression analysis, adjusted for demographic and clinical factors, was used to analyze patient height and weight collected at clinical trial enrollment. RESULTS: Among 23 926 patients (median [IQR] age, 58 [51-66] years; 17 594 [73.5%] female; 969 [4.0%] Hispanic, 2173 [9.1%] non-Hispanic Black, 19 890 [83.1%] non-Hispanic White) enrolled between 1986 and 2016, unadjusted obesity rates increased from 23.5% (in 1986 to 1990 [n = 657]) to 42.3% (in 2011 to 2016 [n = 836]). There was an increasing linear trend in obesity (odds ratio [OR], 1.23 for each 5-year increase; 95% CI, 1.21-1.26; P < .001), which persisted after covariate adjustment for demographic and clinical characteristics. Findings were consistent for the combined prevalence of overweight and obesity. The observed overall increasing trend in obesity prevalence from 1999-2000 to 2015-2016 was greater in trial patients (21.3% [SE = 0.7] to 49.1% [SE = 1.6]) than in US adults (30.5% [SE = 1.5] to 39.6% [SE = 1.6]) (P for trend = .03), but was similar to US cancer survivors (18.9% [SE = 1.9] to 42.2% [SE = 2.1]; P for trend = .31). CONCLUSIONS AND RELEVANCE: This cohort study found that patients with cancer and obesity are currently well-represented in cancer clinical trials, increasing confidence that trial findings are generalizable to patients with obesity in clinical practice. Availability of data on height and weight at diagnosis through cancer registries will enable a more rigorous analysis of obesity prevalence among patients with cancer.