Seminal Vesicle Involvement by Carcinoma In Situ of the Bladder: Clonal Analysis Using Next-Generation Sequencing to Elucidate the Mechanism of Tumor Spread

We present a rare case of urothelial carcinoma in situ (CIS), which invades the prostate and seminal vesicle (SV). A 70-year-old man underwent transurethral resection of bladder (TURB), and the pathologic examination revealed multiple CIS. Although the patient received intravesical bacillus Calmette-Guerin (BCG) therapy following TURB, recurrence of CIS was confirmed in the bladder and left distal ureter at 3 months following BCG. Radical cystectomy was performed due to BCG-refractory CIS. Microscopically, CIS was found throughout the mucosa of the bladder, left ureter, prostatic duct, and both SVs. Next-generation sequencing revealed significant differences in tumor clonality between bladder and SV CIS cells. Among 101 (bladder CIS) and 95 (SV CIS) somatic mutations, only two were shared, and only one gene (ARHGAP23) was common exon coding region gene. In conclusion, multicentric genetic changes, in line with the field-cancerization effect, may result in SV involvement by CIS of the bladder.