Importance: In oncology randomized clinical trials, suboptimal access to best available care at recurrence (or relapse) may affect overall survival results.

Objective: To assess the proportion and the quality of postrecurrence treatment received by patients enrolled in US Food and Drug Administration (FDA) registration trials of systemic therapy in the adjuvant or neoadjuvant setting.

Evidence review: For this systematic review, all trials leading to an FDA approval from January 2018 through May 2023 were obtained from the FDA website and drug announcements. Randomized clinical trials of an anticancer drug in the neoadjuvant or the adjuvant setting were included. Trials of supportive care treatment and treatments given in combination with radiotherapy were excluded. Information abstracted for each trial included tumor type, setting, phase, type of sponsor, reporting and assessment of postrecurrence, and overall survival data.

Findings: A total of 14 FDA trials met the inclusion criteria. Postrecurrence data were not available in 6 of 14 registration trials (43%). Of the 8 remaining trials, postrecurrence treatment was assessed as suboptimal in 6 (75%). Overall, only 2 of 14 trials (14%) had data assessed as appropriate.

Conclusions and relevance: This systematic review found that 43% of randomized clinical trials of anticancer treatment in the adjuvant or neoadjuvant context failed to present any assessable postrecurrence treatment data. In instances in which these data were shared, postrecurrence treatment was suboptimal 75% of the time. The findings suggest that regulatory bodies should enforce rules stipulating that patients have access to the best standard of care at recurrence.