Outcomes and toxicity of oral Fosfestrol in metastatic castration-resistant prostate cancer-a real-world experience

Introduction: Although there are multiple drugs approved for the treatment of metastatic castration-resistant prostate cancer (CRPC), the cost can be a limiting factor in using them in a resource-limited setting. Therefore, less expensive alternatives are the need of the hour. We have been using Fosfestrol which is a cheap and orally administered oestrogen analogue in metastatic CRPC. We carried out a retrospective study to analyse its efficacy and toxicity. Results: A total of 65 patients received Fosfestrol during 2015-2020. The median age was 65 years (range 50-83 years). Thirty-four patients (53%) had other medical comorbidities. Skeletal-only metastasis was the commonest pattern of metastasis (n = 41, 64%) followed by skeletal with nodal metastasis (n = 15, 23%). The majority of the patients had undergone upfront surgical castration (n = 60, 93%). All the patients had adenocarcinoma and 38 patients (58%) had a high Gleason's score. Forty-one patients (63%) had a prostate specific antigen (PSA) response (decrease of & GE;50% in the PSA concentration from the pre-treatment baseline PSA value) and 54 patients (83%) had a symptomatic response. At the end of a median follow-up of 16 months, the median progression-free survival (PFS) was 8.3 months (CI 4.7-11.8) and the median overall survival (OS) was 27.5 months (CI 25.4-29.5). PSA response and prior treatment with abiraterone acetate were found to have a significant association with survival outcomes. Patients with PSA response had better median PFS and OS; while patients who have received prior abiraterone acetate therapy had worse survival outcomes. Twenty-nine patients (45%) received some form of subsequent treatment after stopping Fosfestrol. The most common oxicity observed was thrombosis (n = 9, 13%) followed by gynecomastia (n = 4, 6%). Conclusion: We conclude that oral Fosfestrol is a cheap and effective agent in the armamentarium against metastatic CRPC and warrants further studies in a clinical trial setting.