Efficacy of combined androgen blockade therapy in patients with metastatic hormone-sensitive prostate cancer stratified by tumor burden

OBJECTIVE: To determine the effect of combined androgen blockade with a first-generation anti-androgen on the prognoses of metastatic hormone-sensitive prostate cancer patients stratified by tumor burden. METHODS: We retrospectively analyzed the cases of metastatic hormone-sensitive prostate cancer patients who were treated with androgen deprivation therapy in 2008-2017 at 30 institutions in Japan. To compare the overall survival and progression-free survival rates of the patients treated with castration monotherapy and combined androgen blockade, we carried out a Cox proportional hazards regression analysis using both inverse probability of treatment weighting and instrumental variables methods. High-burden disease was defined as the presence of four or more bone metastases and/or visceral metastasis. RESULTS: Of 2048 patients, 702 (34.3%) and 1346 (65.7%) patients were classified as the low- and high-burden groups, respectively. In each group, >80% of the patients were treated with combined androgen blockade. Although there was no significant between-group difference in the overall survival according to the androgen deprivation therapy method, in the high-burden group the progression-free survival of the combined androgen blockade-treated patients was significantly better than that of patients treated with castration monotherapy: inverse probability of treatment weighting method, hazard ratio 0.49, 95% confidence interval 0.34-0.71; instrumental variables method, hazard ratio 0.80, 95% confidence interval 0.60-0.98. CONCLUSION: In the high-burden group, combined androgen blockade with a first-generation anti-androgen resulted in superior progression-free survival compared with castration monotherapy. For well-selected metastatic hormone-sensitive prostate cancer patients, the use of combined androgen blockade might still have some suitable scenarios.