[711] Pseudoliposarcomatous Changes in the Perinephric Adipose Tissue of Nephrectomy Specimens Mimicking Well Differentiated Retroperitoneal Liposarcoma: Evaluation in 200 Nephrectomies

B Balzer, R Gupta, AJ Lazar, P Rao, MB Amin. Cedars Sinai Medical Center, LA, CA; MD Anderson Cancer Center, Houston

Background: We have anecdotally observed atypical stromal cells in the fibrous septae, lymphoid aggregates and vascular changes in the perinephric adipose tissue in nephrectomy specimens. On occasions these features raised serious consideration for well differentiated retroperitoneal liposarcoma. En-bloc resections for well differentiated retroperitoneal liposarcoma may contain the kidney as perinephric fat may be involved by R-LPS. This study aims to formally evaluate the pseudoliposarcomatous changes noted in the perinephric fat.
Design: Five to eight slides each from 200 nephrectomy specimens performed for renal epithelial tumors were screened to evaluate changes in the perinephric fat. Focus was on features useful in the distinction from R-LPS. Characterization by fluorescent in situ hybridization for MDM2 mutation is currently underway.
Results: A spectrum of mesenchymal changes that may be observed in liposarcoma was variably seen in 22 cases. Cases showed an admixture of variably sized fibrous bands with atypical hyperchromatic stromal cells (n=22), lymphocytic aggregates (n= 12), variation in adipocyte size (n=10), and myxoid areas (n=3). All the cases demonstrated lochkern nuclei at least focally. All of these morphologic features were simultaneously present in 4 cases resulting in marked overlap with R-LPS. None of the cases showed typical lipoblasts, areas of necrosis or mitoses. The renal tumors were most commonly clear cell renal cell carcinoma and 55% of the tumors were pT1; only 2 cases were pT3. None of the cases had a preoperative biopsy.
Conclusions: The diagnosis of a well differentiated liposarcoma is fraught with challenges; various conditions such as such as fat necrosis, atrophic fat, hibernomatous changes, fat predominant angiomyolipoma or fixation artifacts may have cells that simulate lipoblasts. Pseudoliposarcomatous changes in the perinephric adipose tissue have not been previously documented and represent yet another pitfall. Awareness of these changes in nephrectomy specimens is important so as to prevent over diagnosis of well differentiated retroperitoneal liposarcoma.
Category: Genitourinary (including renal tumors)

Wednesday, March 11, 2009 1:00 PM

Poster Session VI # 125, Wednesday Afternoon