[819] Kidney Injury Molecule-1 (KIM-1) Expression in Sarcomatoid Differentiation in Renal Cell Carcinoma (RCC): Implications for Differential Diagnosis of Malignant Spindle Cell Lesions of the Kidney

R Malhotra, PL Zhang, JV Bonventre, R Gupta, MB Amin, P Rao, M Amin. William Beaumont Hospital, Royal Oak, MI; Brigham and Womens Hospital, Boston, MA; Cedars-Sinai Medical Center, Los Angeles, CA; M.D.Anderson Cancer Center, Houston, TX

Background: KIM-1 is a transmembranous protein involved in phagocytosis of injured proximal tubules in the kidney. Recent studies have shown it to be a sensitive and specific marker for RCC particularly those derived from proximal tubules. In this study, we investigate the utility of this marker in distinguishing sarcomatoid differentiation in RCC from potential diagnostic mimics.
Design: 13 cases of sarcomatoid differentiation in RCC (11 clear cell and 2 papillary RCC), 6 dedifferentiated liposarcomas primarily involving the kidney and presenting clinically as RCC, 15 cases of renal angiomyolipomas and one malignant PEComa of the kidney were stained with antibody directed against KIM-1 molecule (clone: AKG7; dilution1:20). Controls for this study included 10 cases of renal parenchyma and 4 cases each of clear cell type and papillary RCC. Staining results were recorded for both intensity (0 - 3+) and extent (negative, focal, moderate, diffuse).
Results: KIM-1 expression was noted in 12 out of 13 cases of sarcomatoid RCC. Staining was diffuse in sarcomatoid areas in 6 cases, with staining intensity ranging from 1+ to 3+. One case showed focal moderate staining. Staining was focal and weak in additional 5 cases and one case was negative. None of the other cases - dedifferentiated liposarcomas, renal angiomyolipomas or PEComa - stained with KIM-1.
Conclusions: KIM-1, a relatively specific marker for proximal tubule associated renal neoplasia, is expressed in a large majority of sarcomatoid RCCs. This finding has potential diagnostic utility in distinguishing between malignant spindle cell lesions involving the kidney, particularly in needle biopsies where the epithelial component of the RCC may not be represented. This immunostaining has a potential role in metastatic settings where accurate diagnosis may have therapeutic ramifications.
Category: Genitourinary (including renal tumors)

Monday, March 9, 2009 2:00 PM

Platform Session: Section A, Monday Afternoon