Abstract 2105: Implications of metastatic stage at presentation in docetaxel naïve metastatic castrate resistant prostate cancer

Abstract Background: Studies on metastatic hormone sensitive prostate cancer have shown that metachronous presentation has a better prognosis compared to synchronous disease. However, it remains unknown if such association is pertinent in metastatic castrate resistant prostate cancer (mCRPC). We performed a secondary analysis of ACIS study to determine if the response to dual androgen receptor axis-targeted therapy (ARAT) in in docetaxel naïve metastatic castrate resistant prostate cancer (mCRPC) varies based on M-stage at diagnosis and if prior local therapy plays an effect modifying role in the association of M-stage at presentation with survival. Patients and Methods: In this phase III randomized controlled trial, mCRPC patients with no prior exposure to androgen biosynthesis signaling inhibitors were randomly assigned to either apalutamide or placebo combined with abiraterone and prednisone. Cox regression models were applied for radiographic progression-free survival (rPFS), overall survival (OS) with interaction terms between M-stage and treatment regimen. Multivariable Cox regression analyses were performed to determine the adjusted association of M-stage with rPFS and OS after considering the effect modification by prior local therapy (LT). Results: Among 972 evaluable patients -432 had M0, 334 had M1 at diagnosis while M-stage was unknown in 206. We did not find any statistically significant heterogeneity of treatment effect on rPFS (interaction p=0.13; HR for placebo in M0 group: 1.42 [1.13-1.79]; M1/unknown group: 1.11 [0.90-1.37]), and OS (interaction p=0.87; HR for placebo in M0 group: 1.02 [0.81-1.29], and M1/unknown group: 1.00 [0.82-1.23]) based on M-stage at diagnosis. There was no significant association of M-stage with rPFS (HR for LT group: 1.08 [0.84-1.40], HR for no LT: 0.91 [0.67-1.24]) and OS (HR for LT: 1.04 [0.81-1.33] and no LT: 0.95 [0.70-1.29]) with no significant heterogeneity depending on receipt of LT (interaction p-value of 0.94 and 0.93, respectively). Conclusion: We did not find a statistically significant heterogeneity in efficacy of dual ARAT based on synchronous versus metachronous presentation. M-stage was not found to be a predictor for rPFS and OS after considering effect modification by prior LT. Citation Format: Shawn Malone, Christopher Wallis, Scott Morgan, Amar Kishan, Amy Tu Trinh Le, Julia Malone, Yilun Sun, Daniel Spratt, Fred Saad, Soumyajit Roy. Implications of metastatic stage at presentation in docetaxel naïve metastatic castrate resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2105.