| Summary: | Abstract Objective The objective of the study is to evaluate whether low nadir testosterone during treatment with triptorelin pamoate, a luteinising hormone‐releasing hormone (LHRH) agonist, is associated with improved clinical outcomes in patients with advanced prostate cancer using a retrospective analysis of clinical trial data. Patients and methods Data were pooled from three prospective, 9–12‐month Phase III studies of triptorelin monotherapy in patients with advanced prostate cancer (including NCT00751790). The serum testosterone concentration suppression targets evaluated were <0.35 nmol/L (<10 ng/dl), <0.7 nmol/L (<20 ng/dl), <1.7 nmol/L (<50 ng/dl) and ≥1.7 nmol/L. Overall survival (OS) and disease‐specific survival (DSS) by testosterone suppression group were assessed by Kaplan–Meier analysis, with log‐rank test. The time frame for the primary analysis was Days 1–518 (median OS follow‐up 254 days [range, 29–518 days]) and for the sensitivity analyses was Days 1–262. Supplementary analyses combined the ≥0.7‐ to <1.7‐nmol/L and ≥1.7‐nmol/L groups. Results The sample size comprised 592 patients (most received triptorelin monotherapy; four reported concomitant androgen receptor‐axis–targeted therapy). Nadir testosterones of <0.35, ≥0.35 to <0.7, ≥0.7 to <1.7 and ≥1.7 nmol/L were achieved by 96%, 3.2%, 0.34% and 0.17% of patients, respectively. Better OS with decreasing level of nadir testosterone was observed (p < 0.001) and this persisted after sensitivity/supplemental analyses (all p < 0.001). Differences in DSS with decreasing levels of nadir testosterone were not statistically significant in the primary analysis. Sensitivity/supplemental analysis showed better DSS with decreasing level of nadir testosterone (Days 1–262, p = 0.01; combined groups Days 1–518, p = 0.03; combined groups Days 1–262, p = 0.005). Conclusion Low nadir testosterone achieved during treatment with the LHRH agonist triptorelin was associated with improved OS and DSS in patients with advanced prostate cancer.
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