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

Abstract

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 patients were identified who had received D of which 50 were evaluable. During D treatment PSA responses were not available for 5 patients, while 16 (35%, 95%CI [20%-50%]) had a ≥ 50% PSAD which was confirmed a month later with a second reading. For the responders, the median duration of PSA response from initiation of treatment to PSAP was 293 days (range: 219 to 1063). After DW, PSAD was observed in 12 patients (24%, 95% CI [12%,36%]). PSAD ≥ 25%, ≥ 30% and ≥ 50% was observed in 6, 3 and 2 patients respectively (12%, 6% and 4%) and in only one could the ≥ 30% PSAD be confirmed with a second reading a month later. In 5 cases of ≥ 25% PSAD, next treatment was initiated despite a dropping PSA, after 8 to 43 days. In one case only was PSAP reached during DW with a response duration of 53 days from DW to PSAP. The frequency of ≥ 25% PSAW responses was not significantly different between patients with and without prior response to dexamethasone: 6% and 17% respectively, Chi-square test p = 0.29. One patient reported improvement of his urinary symptoms after DW. Conclusions: DW responses are observed in a minority of patients. This phenomenon merits further prospective characterization and needs to be considered in the design of clinical trials.