Researchers in Hong Kong wanted to confirm the efficacy of abiraterone acetate (Zytiga) used prior to chemotherapy that had been shown in the trial setting. In their analysis they came up short; raising some very significant concerns about Zytiga’s efficacy when used prior to chemotherapy.
They reviewed the clinical records of men with metastatic castrate resistant prostate cancer (mCRPC) who had been treated with Zytiga from all 6 public oncology centers in Hong Kong between August 2011 and December 2014. They evaluated their treatment efficacy, its determinants and toxicities.
They evaluated 110 men with castrate resistant prostate cancer of whom 58 were still chemo-naive and 52 who had already received chemotherapy (post-chemo). The median follow-up time was 7.5/11.4 months for chemo-naive/post-chemo men. They also found that 6.9/15.4 % of chemo-naive/post-chemo men had visceral metastases.
The median overall survival (OS) and progression-free survival (PFS) were 18.1/15.5 months and 6.7/6.4 months for chemo-naive/post-chemo patients, respectively.
They found that among chemo-naive men, those with visceral diseases had significantly inferior OS (2.8 vs 18.0) and PFS (2.8 vs 6.8 months) than those without visceral disease.
They did find that pain control was comparable in both groups of men.
In multivariate analysis, they found that the presence of prostate-specific antigen (PSA) response (greater than or equal to 50% drop from baseline) within the first 3 months of therapy was associated with favorable OS and PFS in both chemo-naive and post-chemo group.
They concluded that in their study population of men from Hong Kong that in the real life clinical practice outside the trial setting, OS after Zytiga in the chemo-naive cohort (18.1 months) was considerably shorter than that reported in the COU-AA-302 trial (34.7 months), and the OS was particularly short in those men with visceral metastases (2.8 months).
Conversely, Zytiga was efficacious in post-chemo patients.
However, Zytiga resulted in comparable pain control in both groups of men. The presence of PSA response within the first 3 months of treatment was a significant determinant of survival.
This is an important study that now must be evaluated outside of Hong Kong. Clearly, these results have the potential to reverse current clinical practice once we evaluate if their findings are specific to men from Hong Kong, have been influenced by the retrospective nature of the study or are a simple fluke. The FDA needs to insist that additional trials be performed to gather more data.
BMC urology. 2016 Mar 22*** epublish *** Darren M C Poon, Kuen Chan, S H Lee, T W Chan, Henry Sze, Eric K C Lee, Daisy Lam, Michelle F T Chan