COW-2019-01

Q1. C

Invasive urothelial carcinoma, usual type, with abundant myxoid stroma

Invasive urothelial carcinoma with abundant myxoid stroma is a rare tumor initially described by Tavora, et al. and characterized by the presence of abundant extracellular mucin pools within which nests, microcysts and cords of invasive urothelial carcinoma cells are seen floating in the absence of glandular differentiation. As such, true gland formation should not be present. The cytological features vary from high-grade to deceptively bland and the associated papillary component when present can be of high- or low- grade. In another series, Cox, et al. reported similar cases in which a prominent cord-like arrangement reminiscent of chordoma or myxoid chrondrosarcoma was noted. Those cases which were referred to as invasive UC with chordoid features showed significant morphological overlap with the current entity. Regardless of the terminology used, this type of tumors has NOT been recognized as a distinct entity in the latest WHO classification (2016), as the characteristic myxoid background is regarded merely as a distinctive stromal reaction to usual invasive UC.

Importantly, pathologists should not confuse this entity with invasive mucinous adenocarcinomas from the prostate, intestine or bladder. Mucinous prostatic adenocarcinoma typically shows single or cribriform glands with positivity for prostatic markers such as NKX3.1. Mucinous adenocarcinomas originating in the intestine or bladder often display pools of mucin lined by neoplastic glandular enteric-type epithelium with varying degrees of cytologic atypia and intracytoplasmic mucin. In addition, for mucinous adenocarcinomas of intestinal origin, beta-catenin shows typical nuclear positivity and GATA3 is usually negative.

Two additional UC variants that may be considered in the differential diagnosis are micropapillary and sarcomatoid UC. Micropapillary UC, in contrast to UC with abundant myxoid stroma, shows prominent retraction artifact surrounding multiple small tight urothelial nests with peripheral nuclear location. Sarcomatoid UC may be associated with a myxoid stromal reaction, but in addition shows malignant cells with spindle morphology in contrast to the usual UC morphology present in UC with myxoid stroma. Despite its rarity, invasive UC with abundant myxoid stroma does not seem to differ significantly from the usual UC in terms of immunoprofile or clinical behavior.

Tavora F, Epstein JI. Hum Pathol. 2009;40(10):1391-8.
Cox RM, Schneider AG, Sangoi AR, et, al. Am J Surg Pathol. 2009;33(8):1213-9
Samaratunga H, Delahunt B. Pathology. 2012;44(5):407-18

Fadi Brimo, M.D., F.R.C.P. (C)
Pathologist and Associate professor
McGill University Health Center
Glen Site, Office E4-4188
1001 Decarie Blvd
Montréal, QC, H4A 3J1
Fadi.brimo@mcgill.ca

Bladder

urothelial carcinoma, myxoid, stroma, variant