Transdermal Estradiol Patches Show Noninferiority to LHRH Agonists in Prostate Cancer Metastasis-Free Survival

This phase 3 randomized trial investigated transdermal estradiol as an alternative to standard androgen deprivation therapy for prostate cancer management. The study enrolled 1360 men with locally advanced prostate cancer, specifically defined as M0 and N0 or N+ disease. Participants were recruited from 75 U.K. centers and followed for a duration of 36.0 months. The intervention involved tE2 patches delivering 100 μg of estradiol every 24 hours. The comparator group received luteinizing hormone-releasing hormone agonists.

The primary endpoint focused on 3-year metastasis-free survival. Results indicated 87.1% survival with tE2 compared to 85.9% with LHRH agonists. The hazard ratio was 0.96, with the upper limit of the one-sided 95% CI at 1.11. Noninferiority was met based on these statistical parameters, suggesting comparable efficacy in preventing metastasis over the study period.

Secondary outcomes included 5-year overall survival and safety profiles regarding specific adverse events. For 5-year overall survival, 81.1% of patients treated with tE2 survived compared to 79.2% in the LHRH agonist group. The hazard ratio for this outcome was 0.90, with a 95% CI ranging from 0.75 to 1.07. Regarding symptom management, grade ≥2 hot flashes occurred in 8% of the tE2 group versus 37% of the LHRH agonist group. Conversely, grade ≥2 gynecomastia was reported in 37% of patients receiving tE2 compared to 9% in the comparator arm.

Safety data highlighted distinct tolerability profiles between the two treatment arms. Overall adverse event rates for hot flashes were 44% with tE2 versus 89% with LHRH agonists. Gynecomastia adverse events occurred in 85% of the tE2 group and 42% of the LHRH agonist group. The provided data did not report serious adverse events, discontinuations, or general tolerability metrics. This absence of data limits the comprehensive assessment of severe safety risks associated with either regimen.

Funding for this research was provided by Cancer Research U.K. and the U.K. Research Institute Medical Research Council. The input data did not list specific methodological limitations or potential biases. Consequently, external validation or comparison to prior landmark studies in this therapeutic area cannot be detailed based on the available evidence. The study design supports internal validity, but external generalizability depends on the specific U.K. center demographics.

Clinically, these results suggest tE2 was noninferior to LHRH agonists for 3-year metastasis-free survival. The lower incidence of hot flashes may improve quality of life, while the higher incidence of gynecomastia requires patient counseling. Practice decisions should account for these trade-offs in symptom management. Physicians must consider patient preference regarding side effect profiles when selecting between these hormonal therapies.

Several questions remain unanswered regarding long-term outcomes beyond the reported follow-up periods. The lack of reported serious adverse events and discontinuation rates limits the assessment of severe safety risks. Further investigation is needed to understand the full safety profile and long-term efficacy in this population. Understanding the impact on overall survival beyond 5 years remains critical for long-term planning.