Real-world discontinuation and efficacy data of abiraterone acetate/prednisone (AAP) plus androgen deprivation therapy and radiotherapy in localized prostate cancer.

367 Background: Data from STAMPEDE trial confirmed Overall survival benefit for patients with high-risk localized or locally advanced prostate cancer treated with Radiotherapy (RT) plus 24-month Abiraterone/prednisone (AAP) and ADT. Nevertheless, a 17% discontinuation rate in the experimental arm of the trial was reported. Here we present a cohort of patients treated with this regimen at two Institutions. Methods: We conducted a retrospective analysis of patients with localized or locally advanced prostate cancer who underwent treatment with AAP+ADT+RT with at least 18 months of follow-up. Primary endpoint was the discontinuation rate of AAP in the ITT population. Secondary endpoints included PSA decline rate, PSA nadir <0.02 ng/mL and safety. Clinical data were collected from patients’ electronic records. GraphPad Prism software was used for chart design, data comparison and statistical analysis. Results: Overall, 104 patients completed RT (60 Gy in 20#) and met inclusion criteria for this analysis. Of them, 61 (58.7%) patients had N0 disease, while 43 (41.3%) had N1 disease. AAP was discontinued prior the pre-planned two years in 29/104 (27.9%) patients. Among those who discontinued, median duration of AAP was 13.5 mo [3.2-23.5], while median duration of ADT was not reached [6.1-35.9]. Reasons for AAP discontinuation included hepatotoxicity (n=8), heart concerns and oedema (n=7 and 2, respectively), brain fog (n=2), hypokalaemia (n=2), quality of life deterioration (n=5), other (n=3). In total, 73/104 patients (70.2%) reached a PSA nadir <0.02 ng/mL at the 18-month analysis. No significant difference in achieving a PSA < 0.02 ng/mL was seen between those stopping AAP early (20/29 - 69%) and those who didn't (53/75 - 70.7%). Conclusions: Our analysis revealed a notably high rate of early discontinuation of AAP in the real-world setting in patients treated for their localized prostate cancer when compared to what observed in the STAMPEDE trial. Nonetheless, early discontinuation did not negatively impact on short-term treatment efficacy as a possible surrogate for long-term treatment benefit. Future studies on larger populations with longer follow-up are warranted to confirm these results.