Background: The single-arm, open-label, multicenter, phase II Apa-RP study evaluates the biochemical recurrence (confirmed prostate-specific antigen [PSA] > 0.2 ng/mL)-free rate in patients with high-risk localized prostate cancer (HR-LPC) after radical prostatectomy following adjuvant apalutamide and androgen-deprivation therapy. In this substudy, relugolix, an oral gonadotropin-releasing hormone antagonist, was evaluated in combination with apalutamide.
Objective: The aim of this study was to evaluate whether the approved standard maintenance dose of relugolix in combination with apalutamide sustains castrate testosterone levels (< 50 ng/dL).
Patients and methods: Twelve patients with HR-LPC who met all the main study criteria were included in the substudy. Patients received relugolix monotherapy for 2 weeks (loading dose [360 mg] at Day - 14 then 120 mg/day daily until Day - 1), then daily relugolix (120 mg) with apalutamide (240 mg) from Day 1 to Day 28. Endpoints were rate of maintained castration (testosterone < 50 ng/dL) through Day 28 (primary) and safety (secondary).
Results: All 12 patients received relugolix and apalutamide and achieved castrate testosterone levels after 2-week relugolix monotherapy (median testosterone 348.5 ng/dL and 8.7 ng/dL at Days - 14 and - 1). All 11 patients who had testosterone measured at Day 28 maintained castrate testosterone (median 10.0 ng/dL) without relugolix dose adjustment. Treatment-emergent adverse events (TEAEs) occurred in nine patients during relugolix monotherapy and in eight patients during relugolix + apalutamide coadministration. Hot flush was the most common TEAE reported, in six and four patients, respectively.
Conclusions: Relugolix administered at approved standard doses concurrently with apalutamide was effective in maintaining castrate testosterone levels in HR-LPC without new safety signals.
Trial registration number and date: NCT04523207, 21 August 2020.
The Apa-RP study evaluates the combination of apalutamide with drugs that lower male sex hormones for reducing the risk of prostate cancer recurrence. Patients in this study had their prostate gland surgically removed and were at high risk for disease recurrence. Relugolix, a newly approved oral drug for advanced prostate cancer, lowers blood testosterone (the primary male sex hormone) and, in combination with apalutamide, may reduce the risk of prostate cancer recurrence. The Apa-RP substudy goal was to test whether relugolix lowers blood testosterone and maintains these low levels when administered with apalutamide. Researchers looked at the testosterone levels of 12 patients with early prostate cancer who received standard doses of relugolix alone for 2 weeks followed by apalutamide and relugolix for an additional 28 days. Testosterone was measured before and after 2 weeks of relugolix treatment, and then again 28 days after apalutamide was added. All 12 substudy patients achieved low testosterone levels (< 50 ng/dL) after 2 weeks of relugolix treatment. Testosterone was measured at Day 28 of relugolix + apalutamide treatment in 11 patients, all of whom maintained low testosterone without adjustment of their relugolix dose. Adverse effects were consistent with those previously reported for each drug when administered alone. All 12 patients completed the substudy and moved onto the main study, the longer-term results of which will be reported in the future. In summary, relugolix administered at the same time as apalutamide was effective in maintaining low testosterone levels in patients with prostate cancer, without any new safety concerns.
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