Prevalence of oligoprogressive, metastatic castration-resistant prostate cancer (mCRPC) amenable to stereotactic ablative radiotherapy (SABR) in men undergoing abiraterone acetate (AA) therapy.

Abstract

e587 Background: SABR is increasingly used for the treatment of men with oligometastatic prostate cancer, including patients (pts) presenting with oligoprogression. The latter is a clinical situation where a limited number of metastatic tumor sites progress (usually defined as ≤ 3-5), while all other metastases are controlled by a given systemic therapy. The frequency of oligoprogression potentially amenable to SABR is unknown. Methods: Thus, in a retrospective chart analysis we studied the progression pattern of 35 men with chemotherapy-naïve mCRPC undergoing AA therapy, and of 20 men undergoing AA therapy after docetaxel chemotherapy. Applying RECIST1.1 and/or PCWG2 criteria, pts were considered SABR candidates if they radiologically progressed in ≤ 5 distinct metastatic locations, while all other metastases were stable or responding. Results: In chemotherapy-naïve men, pre-AA metastatic lesions were located in bone (94%), lymph nodes (49%), lungs (17%) and liver (3%), whereas progression during AA therapy occurred in bone (89%), lymph nodes (49%), lungs (14%) and liver (9%). 12 pts (34%) fulfilled the criteria of oligoprogression with a median of 2 progressive lesions/pt (range 1-5). 8 pts presented with bone progression only, 3 with nodal progression, and 1 pt with combined bone/nodal progression. Post-docetaxel pts had pre-AA metastatic lesions located in bone (75%), lymph nodes (35%), lungs (5%) and liver (5%). Progression during AA therapy occurred in bone (80%), lymph nodes (75%), lungs (20%) and liver (5%). Only 1 pt met oligoprogression criteria with a single progressive bone metastasis. Conclusions: A sizeable number of men with chemotherapy-naïve mCRPC progressing during AA therapy might be considered for SABR. By contrast, progression of post-docetaxel mCRPC treated with AA is typically widespread. Further efforts are needed to identify criteria for oligoprogressive pts most suitable for SABR with sustained benefit versus men that may progress rapidly with widespread metastases following radiotherapy.