San Francisco, California (UroToday.com) The loss of the RB (retinoblastoma) gene is associated with poor outcome in metastatic castration-resistant prostate cancer (mCRPC) likely because of multiple biological mechanisms including deregulation of androgen receptor signaling activity. The addition of chemotherapy to anti-androgen therapy, especially in patients with loss of RB, may be beneficial. In this study, the authors conducted a phase 2 trial randomizing patients with mCRPC 1:1 to either upfront abiraterone acetate with crossover to cabazitaxel upon treatment failure or combination therapy with abiraterone and cabazitaxel.
Molecular data regarding RB status was captured prior to randomization. Primary outcomes were radiographic progression free survival, and secondary outcomes were overall survival, PSA progression-free survival, objective response rate and toxicity. An exploratory objective of circulating tumor cells for RB and androgen receptor expression was also included.
A total of 81 patients were enrolled on study. Risk stratification per the Halabi nomogram from CALGB 90401 was balanced between arms with 2/3 of patients classified as low risk.
Results from the trial to date show numerical improvement in the combination of abiraterone and cabazitaxel with regards to radiographic progression free survival, PSA progression free survival and PSA decline on therapy. Overall survival is numerically larger. No formal statistical testing results are reported, but this combination does appear to be promising and could warrant further study. The results of the exploratory analysis of circulating tumor cells and RB status was not reported in this poster.
Presented by: Susan F Slovin, MD, Medical Oncologist at Memorial Sloan Kettering Cancer Center, New York, New York
Written by: Alok Tewari, MD, PhD, Medical Oncology Fellow at the Dana-Farber Cancer Institute, Boston, Massachusetts at the 2020 Genitourinary Cancers Symposium, ASCO GU #GU20, February 13-15, 2020, San Francisco, California