Maintenance GM-CSF in patients with castration-resistant prostate cancer (CRPC) who maximized their response to chemotherapy

Abstract

e16155 Background: There is no standard treatment for CRPC patients (pts) who completed chemotherapy. Time to progression (TTP) ranges from 3–6 months after stopping chemotherapy. GM-CSF (GM) is an immune-based growth factor with reported activity in CRPC. We hypothesized that GM maintenance in pts who have maximized their response to chemotherapy could delay TTP or time to next treatment (TNT). Methods: Eligible pts were those with CRPC who completed 10–12 cycles of docetaxel (D) or mitoxantrone (M) chemotherapy without progression; or those who maximized their response to chemotherapy before completing 10–12 cycles. Maximum response was defined as a <10% change in PSA repeated on two occasions with stable disease (SD) radiographically. Enrolled pts received GM at 250 ug/m2 subcutaneously for 14 days followed by 14-days of rest. GM was continued until disease progression. Primary end point was the clinical benefit defined as the sum of partial response (PR), complete response (CR) and SD. Secondary end points included toxicity, TTP, and TNT. Results: To date, 12 pts out of planned 20 have been enrolled (9 were on D and 3 on M). Median age was 78 (66–96). Median PSA at enrollment was 56.5 (0.1–566). Only 1 pt had a Gleason score < 7. Median time from initial diagnosis to GM was 70 months. Median number of chemotherapy cycles prior to GM was 9 (6–12). Eight pts (66%) had visceral and bone disease. GM was well-tolerated with no drug-related grade 3 and/or 4 toxicities. Ten pts are evaluable (1 pt withdrew consent and another did not comply). Median GM cycles received so far was 3 (2–11). With a median follow up of 11 months (2–17), 3 pts demonstrated SD and 2 had PR for an overall clinical benefit of 50%. One pt remains on study at 7 months while the median response duration for the other 4 responding pts was 7 months. Four pts never received another treatment but the median TNT in other evaluable pts was 3 months. Conclusions: GM is safe, well tolerated, and has activity in CRPC after stopping chemotherapy. Combining chemotherapy with GM should be investigated in future studies. [Table: see text]