719 SERUM CONCENTRATION OF TESTOSTERONE MEASURED BY ISOTOPE DILUTION-LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY (ID-LC-MS/MS) IN MEN AFTER BILATERAL ORCHIECTOMY OR LUTEINIZING HORMONE RELEASING HORMONE (LHRH) AGONIST THERAPY

P in chemotherapy-naive patients (pts) with mCRPC, and to assess the frequency of interpretation of bone scans that is discordant with PSA and clinical response. METHODS: COU-AA-002 was a single-arm, open-label, multicenter, phase II study of 1000 mg AA with 5 mg po P BID in continuous 28-day cycles. Primary end point: pts achieving a 50% PSA decline by Week 12. Secondary end points: objective radiographic response (RECIST), time to PSA progression (TTPP), overall survival and clinical benefit of disease stabilization, change in ECOG status and safety. Bone scan flare was evaluated for all pts who had scans available at baseline, 4, and 7 months. RESULTS: Between October 2007 and May 2008, 33 pts with mCRPC were enrolled. A 50% PSA decline at Week 12 was seen in 22 pts (67%). Maximal PSA declines of 50% and 90% were seen in 26 (79%) and 15 (46%) pts, respectively, with undetectable PSA levels ( 0.1 ng/mL) in 2 pts. Overall, an objective tumor response occurred in 9/33 (27%) as partial responses; 2 had stable disease. The median time on therapy was 63 weeks (range, 8 –104 weeks), with 15 (46%) pts still on treatment. Median TTPP was 71 weeks (95% CI; 40 weeks, not estimable). ECOG-PS improved from 1 to 0 in 8 (24%) pts. Bone scan flare was observed in 30% overall and in 10/23 (43.5%) of those who experienced a decline in PSA. Adverse events were mainly grade 1 to 2, with the most common being fatigue (46%), hot flush (30%), bone pain (24%), peripheral edema (24%), arthralgia (21%), dizziness (21%), and hypokalemia (21%). CONCLUSIONS: Clinical response to AA P was frequent and durable in chemotherapy-naive pts with mCRPC, with over 50% on therapy for 1 year. The high rate of bone scan flare indicates that further investigation is needed to clarify the clinical meaning of this phenomenon. AA P was well tolerated. Maturing data from the COU-AA-302 phase 3 study comparing AA/P to placebo/P will further clarify the effects of abiraterone in chemotherapy-naive mCRPC.