Successful treatment of recurrent small cell carcinoma of urinary bladder with pembrolizumab.

Introduction: Small cell carcinoma of urinary bladder is rare and has an aggressive malignant behavior and poor prognosis. Advanced bladder cancers are treated with immune checkpoint inhibitors, however, its efficacy for small cell carcinoma of urinary bladder is unclear.

Case Presentation: A 54-year-old female, diagnosed with clinical stage T2N0M0 small cell carcinoma of urinary bladder, underwent radical cystectomy after three cycles of etoposide-cisplatin neoadjuvant chemotherapy. Despite the fact that pathological examination revealed no residual carcinoma in bladder in her cystectomy specimen, local recurrence of a 60-mm mass detected in the follow-up investigation 7.5 months later. This was completely treated by pembrolizumab without any adverse effects. Immunohistochemical staining revealed that the tumor had no programmed death ligand 1 expression but it showed CD8-positive T-lymphocyte infiltration into the tumor.

Conclusion: Immune checkpoint inhibitors might have curative potentials for treatment of small cell carcinoma of urinary bladder.