Insurance companies in the US are only covering Xtandi for use after Zytiga therapy has failed. This clause for the use of Xtandi requires prior use of Zytiga and have clinically progressed on this treatment. Only then will the insurance companies cover the use of Xtandi. This is probably because Xtandi costs $7,500 per month which is considerably more than Zytiga at $5,000 per month.
However there is no clinicall evidence so far that Xtandi works in Zytiga relapsed patients. Patients who have Zytiga Resistant Prostate Cancer (ZRPC) have tumours that have become completely hormone independent so they are unlikely to respond to another antihormonal therapy such as Xtandi. Zytiga has been shown to work when Xtandi has failed but there is currently no evidence that Xtandi will work when Zytiga has failed.
The trial of the closely related antiandrogen AR-509 shows hope that Xtandi may show reponses after Zytiga, since AR-509 is a closely related analogue of Xtandi, and the clinical trials on AR-509 showed a 10% response rate in prostate cancer patients who had previously received Zytiga. So there is hope that at least some patients may benefit from Xtandi post Zytiga.
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