A 73-year-old Japanese man visited the urology clinic with the chief complaint of gross hematuria in June 2015. His prostate specific antigen (PSA) level was 146.7 ng/ml and he was diagnosed with prostate adenocarcinoma with a Gleason Score of 5+4. With bone metastasis in the right femur (cT3aN0M1), he was treated by orchiectomy and bicalutamide. He had gross hematuria in October 2017 and a prostate tumor was detected by computed tomography (CT) and magnetic resonance imaging without increasing PSA levels. Prostate re-biopsy showed prostate neuroendocrine carcinoma and local radiation therapy (74 Gy) was performed. Follow-up CT revealed a left adrenal tumor with a positive positron emission tomographic scan in October 2018. Under the diagnosis of metastatic neuroendocrine carcinoma, chemotherapy using cisplatinum and etoposide was performed. The tumor shrunk after five courses of treatment, followed by regrowth in April 2019. Radiation therapy (50 Gy) was added to the left adrenal tumor and it shrunk again. However, a left retroperitoneal tumor was detected in July 2019 and it was resected under laparoscopic surgery and diagnosed as metastatic neuroendocrine carcinoma. Since then, no recurrence has been observed.