Objective

Two pivotal clinical trials, both published in June 2017, have demonstrated that abiraterone acetate (AA) combined with androgen deprivation therapy (ADT) significantly extends the survival of metastatic castration-sensitive prostate cancer (mCSPC) patients compared to ADT alone. Yet, the benefits may be pronounced for younger compared with older patients. We aimed to assess whether the publication of the trials’ results was associated with differential AA utilization between age groups.

Methods

We utilized electronic medical records and claims data from the TriNetX platform, collected from healthcare organizations across the United States. Our analysis included newly diagnosed mCSPC patients observed from June 2014 to June 2019. We designed a difference-in-differences (DID) event study to assess the differential uptake rate of AA every six months before and after publication. The dependent variable was a binary indicator of AA initiation. The primary independent variables included time fixed effects (the first pre-publication period, December 2016 to May 2017, was set as reference), an indicator of < 70 years old, and interactions between time fixed effects and age indicator. We employed a linear generalized estimating equation with an exchangeable correlation, adjusting for demographics and clinical conditions.

Results

Our sample included 6,896 newly diagnosed mCSPC patients with a baseline mean age of 71 years. The pre-publication trends of AA use were similar between the groups. Over the two years after publication, the increase in uptake rate was significantly faster among the younger than older, with a DID estimate of 5% (3% – 8%).

Conclusions

Despite the absence of clinical guideline recommendations for differential use of AA between age groups, our study suggests that self-selection might exist due to the evidence of heterogeneity. This finding also warrants attention that the uncertainties of trials’ subgroup analyses might lead to health loss among the older.