PSA levels after dexamethasone withdrawal (DW) in castration resistant prostate cancer (CRPC).

278 Background: PSA decline (PSAD) in CRPC after withdrawal of antiandrogens and steroid related drugs is well established. DW responses have been anecdotal and not well characterized. In this study we investigated the frequency and magnitude of PSA changes after DW. Methods: We retrospectively identified patients treated in the Royal Marsden for CRPC with D monotherapy. Patients were considered evaluable if they had between DW and their next treatment or radiotherapy an interval of at least 7 days, no other intervention and at least one PSA reading. Patients who received radiotherapy during treatment with D or received D for palliation of symptoms were excluded. The number of patients showing PSAD was recorded together with its percentage change from baseline. Chi-square test was used to compare response rates between different groups and 95% confidence intervals (CI) for the description of frequencies. PSA progression (PSAP) was defined according to Prostate Cancer Working Group 2 criteria. Results: 200...