Urothelial carcinoma with abundant myxoid stroma

SummaryUrothelial carcinomas with abundant myxoid stroma have thus far been only briefly reported in a couple of textbooks yet not in the peer-reviewed literature. Thirteen cases of urothelial carcinoma with myxoid features were collected over 9 years. Cases with any distinct adenocarcinoma component were excluded from the study. The mean age of the patients was 64 years (range, 45-84 years). Nine of the 13 were male. All cases involved the bladder with one of the cases involving a bladder diverticulum. Treatment included transurethral resection of the bladder only in 6 patients, transurethral resection of the bladder with subsequent intravesical bacillus Calmette-Guérin treatment in 4 patients, radical cystectomy only in 2 patients, and neoadjuvant chemotherapy followed by cystectomy in 1 patient. In all cases, the myxoid stroma was associated with invasive urothelial carcinoma. The 2 most common patterns of cancer with myxoid stroma were small- or medium-sized nests seen in 10 cases followed by filiform cancer seen in 4 cases. Other patterns of invasive cancer associated with myxoid stroma were short cords and individual cells. The percentage of invasive urothelial carcinoma that had myxoid stroma ranged from 5% to 95% (mean, 50%). An unusual finding was the presence of invasive low-grade urothelial carcinoma associated with myxoid stroma in 5 cases, 4 of which had an overlying low-grade papillary urothelial carcinoma component. All cases were uniformly positive for cytokeratin 7 and negative for CDX2 with 5 cases also positive for cytokeratin 20. Urothelial carcinoma associated with the extracellular myxoid matrix was positive for MUC5 in 3 cases and for MUC2 in 2 cases. Two of the MUC5-positive cases were also positive in the urothelium for polyclonal CEA. Histochemical stains for Alcian blue with and without hyaluronidase, periodic acid–Schiff, and mucicarmine showed positivity in the areas of myxoid differentiation. The current study describes a rare variant of urothelial carcinoma that may be confused with primary or secondary adenocarcinoma of the bladder, which can have therapeutic and prognostic implications.