[894] Variant Histologic Differentiation in Urothelial Carcinoma Is Frequently Under-Recognized and Documented in Community Practice

LP Kunju, RB Shah. University of Michigan, Ann Arbor, MI

Background: Urothelial carcinomas (UCs) have a peculiar capacity for "divergent" or "mixed histology" differentiation comprising of several unusual histologic variants, most of which have been recognized in the WHO 2004 classification. The recognition and documentation of these variants in the pathology report is critical as they have diagnostic, therapeutic and prognostic implications. Our aim was to assess the awareness and reporting practices of variant histology of UCs amongst community pathologists.
Design: All transurethral bladder tumor resections (TURBT) performed at outside institutions and reviewed at our institution prior to instituting therapy, were retrieved from the pathology database. UCs demonstrating divergent histologic differentiation diagnosed at our institution were selected and were compared with pathology reports sent by the referring community pathologists, to assess the differences in documentation of divergent histology. Cases with pure squamous cell carcinoma, adenocarcinoma and sarcoma were excluded. Mixed histologic differentiation was quantitated as focal (10-50%) and extensive (>50%).
Results: Of 589 TUBRT, 115 (19.5%) showed UCs with divergent differentiation. Majority (88%) cases showed a single pattern while 12% showed multiple patterns of divergent differentiation. Overall, 55% cases showed extensive divergent differentiation. Squamous differentiation (32%) was most commonly seen followed by small cell (14%), glandular (13%), micropapillary (10%), nested (8%), sarcomatoid (6%), lymphoepithelial (3%) and plasmacytoid (2%) differentiation. Divergent differentiation was not documented by the contributing community pathologist in 44% (51) cases. Of these 51 cases, divergent histologic differentiation was focal in 57% and extensive in 43% cases. The histologic variants most likely to be under-recognized included lymphoepithelial and plasmacytoid types (100%), followed by micropapillary (86%), nested (75%) and small cell (42%) differentiation. Overall, squamous, sarcomatoid and glandular differentiation had good reporting correlation (≥75%).
Conclusions: Our results suggest that histologic variants of UC are often under-reported and/or under-recognized in community practice, specifically lymphoepithelial, plasmacytoid, nested, micropapillary and small cell types. Increased awareness for recognition and documentation of these histologic variants is needed in order to avoid critical diagnostic misinterpretations.
Category: Genitourinary (including renal tumors)

Tuesday, March 23, 2010 1:00 PM

Poster Session IV # 99, Tuesday Afternoon


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