Xp11.2 translocations in adult renal cell carcinomas with clear cell and papillary features.

4613 Background: Xp11.2 translocation renal cell carcinoma (RCC) is a rare tumor with unpredictable clinical course and prognosis in adults. Recognition of these tumors depends on the identification of a RCC with unique histology, particularly clear cell and papillary (CCP) features. Our objectives were to determine the incidence of Xp11.2 translocations in adult RCCs with clear cell and papillary features, and to characterize the clinicopathological features and prognosis of adult Xp11.2 RCCs. Methods: Slides for 1047 RCCs in adults (1999-2009) were retrieved from multiple institutions. Cases were reviewed histologically in order to detect any degree of clear cell and papillary change. Tissue microarrays were constructed from the clear cell and papillary RCCs as well as 40 non-papillary clear cell, 5 papillary, 3 chromophobe and 2 unclassified RCCs. Immunohistochemistry using TFE3, a marker highly sensitive (97.5%) and specific (99.6%) for Xp11.2 translocations was performed. Four pathologists independently reviewed the TFE3 results. Clinical and pathologic data were also retrieved. Results: Out of 1047 RCCs, 140 (13%) exhibited clear cell and papillary features. Four out of these 140 (3%) were positive for TFE3. All of the non-papillary clear cell, papillary, chromophobe and unclassified RCCs were negative for TFE3. Mean follow up for TFE3+ RCCs was 55 months. Conclusions: Xp11.2 translocation RCCs diagnosed by TFE3 immunohistochemistry were identified in 3% of adult RCCs that had clear cell and papillary changes. These tumors appear to present with smaller tumour size, lower stage and better prognosis in comparison to non-Xp11.2 CCPRCC and clear cell RCCs. In addition to Xp11.2 translocation carcinoma, coexistence of clear cell and papillary features may be present in other subsets of tumors that have yet to be characterized. [Table: see text]