Xp11.2 translocation/TFE3 gene fusion renal cell carcinoma with a micropapillary pattern: cases report and literature review.

Xp11.2 translocation/transcription factor E3 (TFE3) gene fusion renal cell carcinoma (Xp11.2 translocation RCC) was first classified as a distinct type of renal tumor by the World Health Organization in 2004. However, its morphology and clinical manifestations often overlap with those of conventional RCCs. Moreover, a micropapillary pattern (MPP) comprising small papillary cell clusters surrounded by lacunar spaces has never been described in RCC. We compared the clinicopathological and prognostic characteristics of one patient with Xp11.2 translocation RCC exhibiting an MPP (TFE3-M) to those of four patients with conventional Xp11.2 translocation RCC (TFE3-N); all five tumors resembled conventional RCCs on gross pathology. All patients exhibited similar histologies, clinical manifestations, and prognoses, and all underwent radical nephrectomy. However, their characteristics differed significantly from those of other MPP-comprising neoplasms. Both tumor types were positive for TFE3 and vimentin; however, TFE3-M tumor cells expressed epithelial membrane antigen and human melanoma black-45 but not cluster of differentiation 10 (CD10), whereas the TFE3-N cells expressed P504S, CD10, and vimentin but not cytokeratin 7. Our RT-PCR analysis result showed that TFE3-N and TFE3-M tumor cells were identified expressing and fusion genes, respectively. These findings suggest that TFE3-M should be classified as a histological subtype of Xp11.2 translocation RCC, although its relationship with other MPP-exhibiting neoplasms remains unclear. The histological characteristics of Xp11.2 translocation RCCs depend on MiT family transcription factors and their gene fusion partners. Xp11.2 translocation RCC should be considered for malignancies presenting with a particular pattern; such malignancies can be identified reliably by their morphological and immunohistochemical profiles.