A radiation-related second primary gastrointestinal stromal tumor in the bladder

A 69-year-old man underwent 78 Gy/39 Fr of intensity-modulated radiation therapy for prostate cancer. Seven years after radiotherapy, a nonpapillary bladder tumor was identified. Transurethral resection of the bladder tumor was performed, and the pathological diagnosis was spindle cell sarcoma. Immunostaining revealed KIT^-, DOG1⁺⁺, CD34^-, Actin⁺⁺, Cytokeratin^-, Desmin^-, S100 protein^-, and Vimentin⁺⁺. No tumor recurrence was observed until 17 months after tumor resection. DOG1 is strongly and specifically expressed in gastrointestinal stromal tumors. This was a rare case of bladder gastrointestinal stromal tumor as a radiation-related second primary tumor.