Blinding and patient-reported outcome completion rates in US Food and Drug Administration cancer trial submissions, 2007-2017

Background: Patient-reported outcomes (PROs) are commonly included in submissions to the United States Food and Drug Administration (FDA). Open-label designs are frequent in cancer trials. Between-arm differences in PRO missingness may affect results. We sought to compare PRO completion rates between study arms in randomized open-label and double-blind cancer trials.

Methods: Randomized, controlled trials for oncology and malignant hematology products submitted to the FDA in fiscal years 2007-2017 were identified using internal FDA databases. Applicant study reports were reviewed to assess PRO use and reporting of completion rates. Completion rates were collected for each PRO and compared between arms. Results were summarized using descriptive statistics.

Results: Ninety-six trials for anticancer products from 2007 to 2017 contained PROs. Fifty-one (53.1%) were randomized, controlled trials with useable information on PRO completion. The median completion rate for investigational arms was 89.7% (range = 33.7-100.0%) and 88.2% (range = 11.0-100.0%) for control arms. At six months, seven double-blind trials had gaps of at least 10% in at least one PRO between arms; in four trials, these gaps favored the control arm (median difference = 11.5%, range = 10.0-17.0%). For open-label trials, four trials had such gaps, all of which favored the investigational arm (median difference = 28.5%, range = 10.0-69.0%).

Conclusions: Among trials that provided interpretable PRO completion information, completion rates were high. Most trials had comparable completion rates between arms. However, when large between-arm completion rate differences existed, differences favoring the experimental arm were more common in open-label trials compared with double-blind trials. Procedures must be put in place to improve reporting of PRO completion and reduce missingness, particularly in open-label trials.