[782] Large Nested Pattern of Urothelial Carcinoma (UC): 17 Cases of a Novel Variant.

Roni M Cox, Jonathan I Epstein. The Johns Hopkins Hospital, Baltimore, MD

Background: We describe a unique pattern of UC invasion consisting of large, irregular to regular nests with bland cytology.
Design: We prospectively retrieved 17 cases of large nested UC from one of the author's consult files (2004-2010).
Results: Mean patient age was 60.8 years (31-81), 82% male. 15/17 cases were TURBT, 1 a nephroureterectomy, and 1 a radical cystectomy (RC). 14/17 had low grade papillary UC as the surface component, 1 case high grade papillary UC, 1 low grade papillary UC with focal (<5%) high grade component, and 1 no surface component. 15/17 invaded into muscularis propria (MP), 1 into lamina propria (LP) with no MP present, and 1 into smooth muscle indeterminate between muscularis mucosae and MP. In all cases, the invasive component was composed of medium-large nests with irregular to regular shaped borders. 1 showed a verruciform, pushing border into the MP with the nests having central cyst formation. Nuclei lacked hyperchromasia with only mild-moderate nuclear atypia. Occasional slightly enlarged, hyperchromatic nuclei with small-indistinct nucleoli were noted. In 4 cases there was focal and 1 case more extensive necrosis. The mean mitotic count per 10 HPFs was 5.5 (range 0-39). A mild-moderate fibrous and/or inflammatory stromal reaction was present surrounding the nests in 13/17 cases with in 1 case a marked reaction; the remaining 3 cases had no stromal reaction. In 12/17 cases, the large, bland nests were the only invasive component present. Focal (<5%) areas of conventional invasive UC were identified in 4/17 cases; 1 case had an invasive component comprised of 70% large nests and 30% conventional UC. 1/17 cases had angiolymphatic invasion. 4 cases had subsequent RC available for review. 2/4 RC's had no residual carcinoma, 1 had large nested UC in MP, and 1 had mixed large nested UC and focal conventional UC invading through the MP into perivesicle tissue. Clinical follow-up was available for 15/17 patients [mean f.u. 35.8 months (5-52 mos)]. 3/15 developed metastatic disease (2 lung, 1 unknown) with 2 of these dead of disease; another patient was dead of disease with no known details. Of the 3 patients that died of disease, 2 had no and 1 had focal (<5%) conventional invasive UC on TURBT.
Conclusions: These cases which posed great diagnostic difficulty both for contributing pathologists as well as for the consultant represent the first description of a large nested pattern of UC that is distinguished from an inverted growth pattern of non-invasive UC by either MP invasion, irregularly infiltrating nests, or a stromal reaction. These tumors despite bland cytology have metastatic potential.
Category: Genitourinary (including renal tumors)

Tuesday, March 1, 2011 9:00 AM

Platform Session: Section A, Tuesday Morning

 

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