Urothelial carcinoma with abundant myxoid stroma.

Urothelial 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.