Multicenter prospective study of switching from GnRH agonists to GnRH antagonist for patients with early stage of castration resistant prostate cancer as a second-line hormonal therapy.

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183 Background: It was reported that GnRH antagonist could extend progression free survival for prostate cancer patients significantly longer than GnRH agonist in a first line hormonal therapy. However, the usefulness of switching from GnRH agonist to GnRH antagonist as a second hormonal therapy remains obscure. We performed a multicentral prospective study to investigate whether the switching from GnRH agonist to GnRH antagonist (degalerix) for patients with castration resistant prostate cancer (CRPC) as the 2nd line hormonal therapy was effective. Methods: 37 patients who were pathologically diagnosed as prostatic adenocarcinoma and developed CRPC after 1st line hormonal therapy with GnRH agonist plus anti-androgens were enrolled. After confirming anti-androgen withdrawal syndrome, they were treated with switching from GnRH agonists to degalerix. The primary endpoint was PSA response (PSA decline or up to 10% over baseline PSA). Secondary endpoints were the time to 25% PSA increase from the baseline (PSA response time), PSA progression free survival (PPFS), the time to treatment failure, cancer specific survival, radiographic PFS (rPFS), and safety. Results: Mean age was 76 years old, super high risk; 20 cases (54.1%), high risk; 11 cases (29.7%), intermediate risk; 5 cases (13.5%), low risk; one case (2.7%). PSA responder rate was 24.3% (9 cases). In responders, the median PSA response time was 5.75 months, the median PPFS was 1.77 months, and rPFS rate at 3 months was 96%. Regarding safety, only 2 cases (5.4%) showed G3 of AE. The PSA response had no relationship with the change of serum testosterone, LH nor FSH. Conclusions: The effectiveness of switching from GnRH agonist to GnRH antagonist showed to be limited. Although no predictive factor of the switching was recognized, some long-term responders were seen. We expect the possibility of switching to GnRH antagonist for patients in the early stage of CRPC, especially non-metastatic status. Clinical trial information: UNKNOWN.