Salvage focal brachytherapy in castration-resistant prostate cancer with neuroendocrine differentiation after radiation therapy

Introduction: Treatment strategy for castration-resistant prostate cancer with neuroendocrine differentiation after radiation therapy has not been established. Case presentation: We described a case of castration-resistant prostate cancer with neuroendocrine differentiation after initial external beam radiotherapy followed by salvage androgen deprivation therapy. Magnetic resonance imaging detected recurrence of a suspicious lesion in the left lobe of the prostate, although the prostate-specific antigen level was <0.2 ng/mL. Transperineal prostate saturation needle biopsy detected adenocarcinoma with neuroendocrine differentiation. The patient underwent salvage focal brachytherapy and had a prostate-specific antigen progression-free survival of 20 months with no obvious adverse events. No recurrence has been detected on magnetic resonance imaging for 18 months. Conclusion: Salvage focal brachytherapy for prostate cancer after external beam radiotherapy can be one of the treatment strategies for local recurrence of castration-resistant prostate cancer with neuroendocrine differentiation.