Background: Knowledge of treatment assignment may affect patient-reported outcomes (PROs), which is of concern in oncology, where open-label trials are common. This study measured the magnitude of open-label bias by comparing PROs for similar patient groups in oncology trials with different degrees of concealment.

Methods: Individual patient data from ipilimumab arms of two melanoma and docetaxel arms of two non-small cell lung cancer (NSCLC) trials were adjusted for differences using propensity score weighting. Patients were aware of treatment assignment in CA184-022 and CheckMate 057 ("open-label"), but not in MDX010-20 and VITAL ("blinded"). Overall survival (OS) and mean changes from baseline to week 12 in EORTC QLQ-C30 (melanoma) and LCSS (NSCLC) scores were compared between open-label and blinded groups.

Results: After adjustment, baseline characteristics were balanced between blinded (melanoma, n = 125; NSCLC, n = 424) and open-label groups (melanoma, n = 69; NSCLC, n = 205). Study discontinuation and PRO completion rates at week 12 and OS were similar. There was no clear direction in differences in change scores between groups. In the melanoma trials, role functioning (mean [95% confidence interval [CI]]=-5.2[-15.4, 5.0]), global health status (-1.3[-8.7, 6.1]), pain (6.2[-1.8, 14.2]) favored the blinded while emotional functioning (2.2[-5.8, 10.2]) and diarrhea (-8.3[-17.3, 0.7]) favored the open-label group. In the NSCLC trials, changes in dyspnea (5.4[-0.7, 11.5]) favored the blinded and changes in appetite (-1.2[-8.1, 5.7]) favored the open-label group. None were clinically/statistically significant.

Conclusions: This study adds to the growing evidence demonstrating that concerns regarding open-label bias should not prohibit the interpretation of large and meaningful treatment effects on PROs.