Targeting FSH in androgen-independent prostate cancer: abarelix for prostate cancer progressing after orchiectomy
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Tomasz M Beer1, Mark Garzotto, Kristi M Eilers
1Division of Hematology and Medical Oncology, Oregon Health and Science University, Portland, Oregon 97239, USA.
Objectives:
To determine the efficacy of the gonadotropin-releasing hormone antagonist abarelix in patients with androgen-independent prostate cancer progressing after orchiectomy and to measure its effect on serum follicle-stimulating hormone (FSH).
Methods:
Sixteen patients with prostate cancer progressing after orchiectomy received abarelix-depot 100 mg by intramuscular injection on days 1, 15, and 29 and then every 28 days for up to 24 weeks (52 weeks in patients who met the criteria for a prostate-specific antigen [PSA] response after 24 weeks). PSA response was the primary endpoint and was defined as a 50% reduction confirmed 4 weeks later. The time to progression and effect of therapy on serum FSH were secondary endpoints.
Results:
No patient met the criteria for a PSA response. Five patients (31%, 95% confidence interval 11% to 58%) experienced confirmed reductions in the PSA level ranging from 9.3% to 31.8%. At the end of the six cycles of therapy, 6 patients remained stable without PSA progression or other signs of disease progression. The median time to progression was 12 weeks (95% confidence interval 6 to 18). The mean serum FSH concentration declined after 4 weeks of study treatment by nearly 90% from a baseline of 45.1 IU/L (95% confidence interval 34.0 to 56.2) and remained suppressed throughout the observation period. Treatment was well tolerated, with one grade 3 allergic reaction.
Conclusions:
Treatment with abarelix in patients with androgen-independent prostate cancer after orchiectomy results in marked reduction in circulating FSH. None of the patients met the PSA response criteria; nonetheless, minor reductions in serum PSA were observed in 5 of 16 patients.
Insights
Abarelix significantly reduced follicle-stimulating hormone (FSH) in men with advanced prostate cancer. While no patients achieved the primary prostate-specific antigen (PSA) response, some showed minor PSA reductions and disease stabilization.
Area of Science:
- Oncology
- Endocrinology
Background:
- Androgen-independent prostate cancer (AIPC) progression after orchiectomy presents a therapeutic challenge.
- Hormonal therapies aim to suppress androgens, but efficacy can be limited.
Purpose of the Study:
- To evaluate the efficacy of abarelix, a gonadotropin-releasing hormone (GnRH) antagonist, in patients with AIPC.
- To assess the impact of abarelix on serum follicle-stimulating hormone (FSH) levels.
Main Methods:
- A phase II study involving 16 patients with AIPC progressing post-orchiectomy.
- Abarelix depot (100 mg) administered intramuscularly at specified intervals for up to 24 weeks.
- Primary endpoint: prostate-specific antigen (PSA) response (50% reduction confirmed 4 weeks later).
- Secondary endpoints: time to progression and serum FSH levels.
Main Results:
- No patient achieved the primary PSA response criteria.
- Five patients (31%) demonstrated confirmed PSA level reductions (9.3%–31.8%).
- Median time to progression was 12 weeks; 6 patients had stable disease.
- Mean serum FSH concentration decreased by nearly 90% within 4 weeks and remained suppressed.
Conclusions:
- Abarelix treatment led to a significant reduction in circulating FSH levels in patients with AIPC.
- Despite not meeting PSA response criteria, abarelix showed potential for minor PSA reduction and disease stabilization in some patients.
- Abarelix was generally well-tolerated, with one instance of a grade 3 allergic reaction.
