Small-Cell Carcinoma of the Bladder With Concurrent High-Grade Prostate Cancer: A Case Report and Review of the Literature.

Small-cell carcinoma of the bladder (SCCB) is a rare, aggressive neuroendocrine malignancy associated with early metastasis and poor survival. Due to its rarity, optimal management is not well defined and is generally extrapolated from small-cell lung cancer treatment paradigms. We report a rare case of SCCB with synchronous high-grade prostate adenocarcinoma managed with a bladder-preserving multimodal approach. An 82-year-old man presented with hematuria and urinary retention, who was diagnosed with limited-stage SCCB following transurethral resection of bladder tumor (TURBT). He received neoadjuvant cisplatin and etoposide, but definitive therapy was significantly delayed due to severe necrotizing perineal infection with fistula formation requiring multiple surgical interventions. During this period, he was also diagnosed with high-risk prostate adenocarcinoma (Gleason 4 + 5 = 9, prostate-specific antigen (PSA) > 100 ng/mL, with normal PSA range less than or equal to 4 ng/mL) and was initiated on androgen deprivation therapy. After recovery and surgical repair of a large inguinal hernia (that would have hindered external beam radiation therapy planning), he underwent definitive bladder-preserving radiotherapy using simultaneous integrated boost volumetric modulated arc therapy (VMAT), delivering 60 Gy in 20 fractions to the prostate and proximal seminal vesicles, 55 Gy in 20 fractions to the whole bladder, and 44 Gy in 20 fractions to the elective pelvic lymph nodes. Treatment was well tolerated with minimal toxicity. Follow-up cystoscopy and imaging demonstrated a complete response in both malignancies. More than three years after treatment, the patient remains without evidence of disease, with a low PSA and no evidence of local, distant, or intracranial recurrence on serial brain magnetic resonance imaging (MRI) studies. This case demonstrates that durable long-term disease control in SCCB may be achievable with individualized bladder-preserving multimodal therapy, even in the setting of significant treatment delays, severe intercurrent complications, and synchronous high-grade prostate cancer. It also highlights the feasibility of simultaneous integrated pelvic radiotherapy for dual malignancies and supports MRI surveillance as a reasonable alternative to prophylactic cranial irradiation in carefully selected patients with SCCB.