Mucin‐producing urothelial‐type adenocarcinoma of the prostate diagnosed after robot‐assisted radical prostatectomy

INTRODUCTION: Mucin‐producing adenocarcinoma of the prostate is a rare disease that includes prostate adenocarcinoma with mucus production, secondary adenocarcinoma from the bladder or colorectum, and adenocarcinoma from the urothelium of the prostatic urethra. We describe prostate‐specific antigen‐negative mucin‐producing urothelial‐type adenocarcinoma of the prostate. CASE PRESENTATION: The patient had urinary retention and a serum prostate‐specific antigen level of 0.74 ng/mL. Computed tomography and magnetic resonance imaging revealed a prostate tumor with a mucous component. We diagnosed adenocarcinoma by prostate biopsy and subsequently performed robot‐assisted radical prostatectomy. Mucin‐producing urothelial‐type adenocarcinoma of the prostate was diagnosed by pathological examinations. Lung metastasis, developing within 3 months after surgery, was treated using chemotherapy. CONCLUSION: Endocrine therapy is ineffective for mucin‐producing urothelial‐type adenocarcinoma of the prostate. Mucin‐producing urothelial‐type adenocarcinoma of the prostate diagnosis requires pathological and immunohistochemical analyses. It is important to surgically remove the primary lesion, and robot‐assisted radical prostatectomy may provide an effective approach. Multimodal therapy is essential to treat for mucin‐producing urothelial‐type adenocarcinoma of the prostate.