Cytological diagnosis of Xp11 translocation renal cell carcinoma: An unusual suspect in bone metastases from unknown primary malignancies

Background: Renal cell carcinoma (RCC) constitutes 3% of all cancers, with a higher incidence in patients with age between 60 and 70 years. RCC frequently present as a metastatic tumor at diagnosis, and bones represent one of the most frequent sites. Many cases, mainly in young patients, includes the Xp11 translocation RCC. The cytological diagnosis of Xp11 translocation RCC in adult population it is rarely performed, likely for the morphological overlap with other adult renal cell carcinoma subtypes. Methods: We retrospectively analyze a series of 92 adult patients with metastatic bone tumors, diagnosed on fine-needle aspiration cytology (FNAC) samples, focusing mainly on the cytological, immunophenotypic and molecular features of Xp11 translocation RCC. Results: In our series 6 of 92 (6.5%) cases were metastatic RCC (mRCC), among them 2 cases were metastasis from Xp11translocation RCC. Those cases showed a bloody background, with several groups of atypical cells arranged in syncytial groups or in papillary groups composed by atypical cells with abundant cytoplasm, with scattered clear cells. TFE3 was positive on immunocytochemical analysis and specific translocation t(Xp11.23) was detected by FISH analysis. Conclusions: In adult patients with mRCC, it is necessary to consider also Xp11 translocation RCC among the diagnostic hypotheses. FNAC represents a valid tool to investigate bone lesions but cytological features of Xp11 translocation RCC are still poorly described and must necessarily be better defined.