Editor's Commentary - Phase II study of abiraterone acetate in chemotherapy-naive metastatic castration-resistant prostate cancer displaying bone flare discordant with serologic response

BERKELEY, CA (UroToday.com) - Dr. Charles Ryan and collaborators published a phase II trial of abiraterone acetate (Zytiga, AA) in chemotherapy-naïve metastatic castration-resistant prostate cancer (CRPC) patients.

Of particular study interest was “bone flare,” defined as a radiologist’s report indicating disease progression after 3 or more months of therapy in the context of a ≥50% decrease in PSA with bone scan improvement or stability 3 months later. In addition to the durable clinical responses to AA, they found bone flare to be common and confounding to interpret.

Men with CRPC were treated in a single-arm, open-label multicenter phase II study with AA 1,000mg daily with prednisone 5mg twice daily until disease progression. Tumors were evaluated with bone scan, CT, MRI or other imaging modalities. This was repeated every 3 cycles. The primary endpoint was the proportion of patients achieving a ≥50% decline in PSA. Bone scan flare was defined as discordant interpretation of the bone scan and a ≥50 decline in PSA.

A total of 33 men were enrolled between 2007 and 2008. Median baseline PSA was 23ng/ml, and all men had radiographic evidence of metastatic disease and 79% had bony metastasis. While all 33 men were evaluable for response and safety, only 23 were evaluable for the bone flare issue. The PSA primary endpoint was met in 67% of men, and in 2 men the PSA became undetectable. The median time to PSA progression was 16.3 months and 19 men received treatment for at least 12 months. Among thirteen patients with measurable disease, 9 (69%) had a partial response and 3 (23%) had stable disease. Among 23 patients with bone scans at 3 months, 12 men (52%) had progression according to the radiologists’ reports. There was subsequent improvement at the next bone scan in 4/12 and stable disease in 7/12. Thus the bone flare with subsequent improvement or stability was noted in 4/23 men (17%) and 7/23 men (30%) of evaluable patients and 4/33 (12%) and 7/33 (21%) of enrolled men, respectively. Most adverse events were grade 1 or 2.

Ryan CJ, Shah SK, Efstathiou E, Smith MR, Taplin ME, Bubley GJ, Logothetis CJ, Kheoh T, Kilian C, Haqq C, Molina A, Small EJ

 

Clin Cancer Res. 2011 Jul 15;17(14):4854-61
doi: 10.1158/1078-0432.CCR-11-0815

PubMed Abstract
PMID: 21632851

UroToday.com Prostate Cancer Section

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