A systematic review of randomized clinical trials (RCTs) in 10 obesity-related cancer types revealed that information on the eligibility and enrollment of obese participants in cancer RCTs is underreported. The authors led by Professor Ludovic Trinquart of the Boston University School of Public Health, Boston, MA, USA urged in the Annals of Oncology for more transparency to understand the applicability of obesity-related cancer RCT results to obese patients with cancer.

Obesity is a risk factor for numerous cancer types and may influence cancer treatment outcomes. Underrepresentation of obese patients in obesity-related cancer RCTs may affect the generalizability of results, the authors wrote in the study background.

The authors conducted a systematic review of RCTs in patients with esophageal, colon/rectal, liver, gallbladder, pancreatic, postmenopausal breast, endometrial, ovarian, kidney, and thyroid cancers. In particular, they selected RCTs published between 2013 and 2016 in 5 major journals.

For each trial, the study team examined the article, the protocol, and the registration record. Furthermore, they assessed if eligibility criteria limiting the enrol'ment of obese participants were reported, the proportion of obese participants that were enrolled, and if a subgroup analysis according to obesity status was reported. They systematically contacted corresponding authors and asked for information about eligibility of obese participants and the proportion of obese participants.

In total, 76 RCTs were included in the analysis of colon/rectal, postmenopausal breast, and kidney cancers being the most frequently studied types.

Based on available public sources, information on the eligibility of obese participants was available in 7% of trials. The proportion of obese participants could be estimated in 12% of trials only. The investigators found a subgroup analysis in only one RCT.

In terms of unpublished information, the eligibility of obese participants was explicitly stated in 41% of trials, but it was unclear if the remaining 59% of trials considered obese participants as eligible and what proportion of obese participants was included. Across 22 trials, the median proportion of obese participants included was 18%.