[712] Dedifferentiated Liposarcoma (De-Diff LPS) Presenting as a Primary Renal Mass Resulting in a Nephrectomy: A Report of 8 Cases with Discussion of Differential Diagnostic Implications

B Balzer, R Gupta, P Rao, GP Paner, M Amin, JK Mckenney, AJ Lazar, MB Amin. Cedars Sinai Medical Center, LA, CA; MD Anderson Cancer Center, Houston; Loyola University Medical Center, Maywood; William Beaumont Hospital, Royal Oak; Stanford University, Palo Alto

Background: When occurring alone, well differentiated retroperitoneal liposarcomas (R-LPS) are relatively easy to diagnose radiologically; when dedifferentiation occurs the typical fat densities may be absent rendering the neoplasm difficult for radiologic diagnosis of an R-LPS. We describe 8 cases of nephrectomies performed for clinically and radiologically suspected primary renal neoplasms, which eventually led to the detection of R-LPS.
Design: Seven cases histologically presented as a sarcoma involving the kidney or hilar region in which histopathologic evaluation of the spindle cell malignancy and the perinephric fat resulted in the diagnosis of de-diff LPS; one was a clear cell RCC with perinephric liposarcoma.
Results: Patients' age ranged from 41-81 years occurring equally in males and females. The tumor size ranged from 5- 25cm. Three tumors showed meningothelial-like whorls mimicking a metanephric stromal tumor or follicular dendritic cell tumor resulting in a work up for these diagnoses. Four cases showed high grade spindle cell morphology including chondroid differentiation in one case, resulting in work up for sarcomatoid carcinoma and primary renal sarcoma. A panel of immunohistochemical stains, CK, S100, desmin, actin, HMB45, CD21, CD35 (all negative) was not supportive of a particular diagnosis. All cases with meningothelial whorls were CD 34 positive. Observation of atypical hyperchromatic cells and/or lipoblasts in the perinephric fat resulted in the diagnosis of liposarcoma.
Conclusions: The differential diagnoses of high grade spindle cell tumors involving the kidney include sarcomatoid change in renal cell carcinomas (RCC) and mesenchymal neoplasms primarily involving the kidney or metastatic to it. Our experience indicates that in cases not conforming to any of the more specific diagnoses, consideration should be given to the possibility of de-diff LPS with attention to the histology of the perinephric fat. The appropriate characterization in such cases has significant clinical implications as liposarcoma is typically not suspected by the urologist and the treatment approach is different than that for a primary renal spindle cell malignancy.
Category: Genitourinary (including renal tumors)

Wednesday, March 11, 2009 1:00 PM

Poster Session VI # 126, Wednesday Afternoon