Systemic treatment for coexisting mucinous urethral adenocarcinoma and prostate adenocarcinoma

INTRODUCTION: Mucinous urethral adenocarcinoma is a rare and progressive cancer of the prostatic urethra. Reports on palliative systemic treatment for mucinous urethral adenocarcinoma are few. We present a case of coexisting mucinous urethral and prostate adenocarcinomas managed with systemic treatment. CASE PRESENTATION: A 66‐year‐old man presented with gross hematuria and urinary retention. Prostate‐specific antigen level was elevated, at 99 ng/mL, and prostate biopsy revealed moderately to poorly differentiated adenocarcinoma. Hormone therapy and standard chemotherapy for prostate adenocarcinoma were ineffective. Prostate re‐biopsy revealed coexisting mucinous urethral and prostate adenocarcinomas. Gemcitabine + cisplatin chemotherapy and folinic acid + 5‐fluorouracil + irinotecan chemotherapy temporarily suppressed the cancer, but 14 months after presentation, he developed liver metastasis and died. Autopsy revealed metastasis of both mucinous urethral adenocarcinoma and carcinosarcoma. CONCLUSION: Mucinous urethral adenocarcinoma is difficult to diagnose in coexistence with prostate adenocarcinoma. This was an extremely rare case showing chemoresistance due to epithelial‐mesenchymal transition.