The difference in serum testosterone recovery between Gn-RH Antagonist and LH-RH agonist among patients with prostate cancer treated with radiation therapy.

382 Background: Only limited data exist related to the serum testosterone (TST) recovery after discontinuation of Gn-RH antagonist (Degarelix acetate). In the present study, we investigated the difference in serum testosterone (TST) recovery between LH-RH agonist and Gn-RH antagonist among prostate cancer (Pca) patients received radiation therapy in combination with androgen deprivation therapy (ADT). Methods: We analyzed the association between TST levels after the end of endocrine therapy and clinical factors in 130 patients who underwent ADT for prostate cancer at Chiba University hospital between May 2003 and May 2020. The proportional hazards model and Kaplan-Meier methods were used for the statistical analysis. Results: The median patient age and PSA were 72 years, and 16.8ng/mL, respectively. The median initial TST and nadir TST were 457 ng/dL, and 20ng/dL, respectively. The median duration of ADT was 857 days. As factors affect the speed of recovery to the castration level (TST 50 ng/dL), univariate analysis showed that Gn-RH antagonist presented the significantly shorter TST recovery compared to those of LH-RH agonist (HR 1.9, p=0.0078), together with the duration of hormone therapy (857 days) and Nadir TST level (20 ng/dL), GS8 and PSA (16.8ng/mL). Multivariate analysis showed that Nadir TST level was an independent predictor (HR 2.0, p=0.0093). As factors affect the speed of recovery to the physiological level (TST 200 ng/dL), univariate analysis showed that Gn-RH antagonist presented the significantly shorter TST recovery compared to those of LH-RH agonist (HR 2.1, p=0.0064). Multivariate analysis showed that duration was the only independent predictor (HR0.34, p=0.0029). Kaplan-Meier curve demonstrated shorter time for the TST recovery in Gn-RH antagonist compared to the LH-RH agonist for the castration level (p=0.0064) and the physiological level (p=0.0052). Conclusions: TST recoveries were significantly shorter in Pca patients treated with Gn-RH antagonist than LH-RH agonist. Nadir TST value, duration, and a type of LH-RH drug may comprehensively suggest us the dynamics of TST recovery after ADT. [Table: see text]