Activity of new agents (NAs) as third-line treatment in metastatic castration-resistant prostate cancer (mCRPC) patients (pts) showing a primary resistance (PRes) to NAs-based second line therapy after docetaxel (DOC): Preliminary results from a multicenter Italian study.

Abstract

216 Background: The androgen receptor machinery remains the ultimate target of NAs in mCRPC post-DOC, abiraterone acetate (AA), cabazitaxel (CAB), and enzalutamide (ENZ). It is postulated that some mechanisms of resistance may be common to all NAs. This may be crucial in planning their sequential use, mainly when a PRes to one of them is observed. The present study assessed the activity of NAs in pts who previously experienced a PRes to another NA administered after DOC. Methods: We collected data of pts who received sequentially two NAs after DOC in 32 Italian hospital. For each pt we recorded the clinical outcomes of all treatments received after DOC. For the study purpose, we consider with PRes all pts progressing within 3 months after second line NA start. All other pts were considered as without PRes. Results: A consecutive series of 271 mCRPC pts, median age 71 yrs (46-91), with bone (89%), nodal (56%) or visceral (19%) mets, was collected. All pts received NAs as second line after DOC (AA 54% – CAB 34%– ENZ 12%) and 54 (20%) showed a PRes. Among these, third line treatment [AA (31%), CAB (42%), and ENZ (27%)], produced a biochemical and an objective response rate of 11% in both cases, with a median progression free survival (PFS) and a median overall survival (OS) of 4 mos and 8 mos, respectively. No statistically significant differences were observed in terms of clinical outcomes on the basis of NA sequences (see Table). Conclusions: It appears from this preliminary data, that the activity of NAs in pts showing a PRes to second line NAs is very limited, regardless the NA is administered. [Table: see text]