[1011] Characterization of Fibromuscular Pseudocapsule of Renal Cell Carcinoma

Leonardo P Roquero, Oleksandr N Kryvenko, Nilesh S Gupta, Min W Lee. Henry Ford Health System, Detroit, MI; Johns Hopkins Hospital, Baltimore, MD

Background: Fibromuscular pseudocapsule (FMP) in renal cell carcinoma (RCC) has been described but little is known about its prevalence and significance. The aim of this study is to further characterize FMP in clear cell (CCRCC), chromophobe (CHRCC) and papillary RCC (PRCC).
Design: 120 consecutive cases of RCC were analyzed for the presence of FMP (defined as parallel bundle of fibromuscular tissues encircling more than 2/3rd of tumor interface with uninvolved parenchyma). RCC at renal capsule or at renal hilum were excluded. FMP was arbitrarily graded: Grade 1 – FMP thickness comparable to adjacent muscular vessel; Grade 2 – FMP thickness more than twice the diameter of adjacent muscular vessel; and Grade 3 – grade 2 findings with vasculopathy (myxoid change, elastic fiber disruption and/or intimal fibroplasia). Tumor size, degenerative changes, and percent tumor regression, and Fuhrman nuclear grade (FNG) were also evaluated. Selected cases were stained with elastic silver stain, Alcian blue pH 2.5, SMA, and CD31.
Results: 105 cases were eligible for the study (44 CCRCC, 44 CHRCC, and 17 PRCC). More CCRCC had FMP (89%, 39/44), than CHRCC (30%, 13/44) and PRCC (35%, 6/17). Average tumor size with FMP was 3.9 cm and 3.7 cm without FMP. Grade 2 FMP was common in CCRCC (56%, 22/39), while CHRCC and PRCC had grade 1 in 77% (10/13) and 83% (5/6) cases, respectively. Grade 3 FMP was only seen in CCRCC (10%, 4/39). CCRCC had more extensive tumor regression (19%, 0-90%) than CHRCC (7%, 0-40%) and PRCC (14%, 0-90%). No correlation was noted with hemorrhagic and cystic changes, tumor size and grading of FMP. The sinusoidal-like vasculature of CCRCC was focally seen in CHRCC. FNG 2 was the predominant grade in CCRCC (50%) and PRCC (53%). Grade 3 was present in 34% CCRCC (15/44) and 29% PRCC (5/17). There were no FNG 4 tumors. FMP was common in lower grade CCRCC (64%, 25/39) and PRCC (83%, 5/6). SMA and CD31 showed linear slit-like endothelium-lined spaces within the FMP. Arterial elastic membrane disruption or fibrointimal mucin deposits were present in grade 3 FMP.
Conclusions: FMP is rather characteristic of CCRCC, less frequent in CHRCC and rare in PRCC. The smooth muscle in FMP may be vascular in origin and may represent complex vasculopathy presumably from increased intratumoral vascular pressure of sinusoidal vascular network. Tumor regression and degenerative changes in relation to FMP need to be further elucidated.
Category: Genitourinary (including renal tumors)

Tuesday, March 5, 2013 9:30 AM

Poster Session III # 93, Tuesday Morning


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