To date, only a few cases of "rosette forming t(6;11), HMB45-positive renal carcinoma" have been published. In this article, we contribute further data on 4 cases of this rare entity. Patients were 3 women and 1 man with an age range of 20 to 54 years (median, 23 years). Follow-up (range, 3-5 years; median, 4 years) did not reveal any metastatic events or recurrences. All tumors were well circumscribed and mostly encapsulated with homogeneous gray to tan cut surfaces. No necrosis was seen. All tumors displayed a solid or solid/alveolar architecture and contained occasionally long and branching tubular structures composed of discohesive neoplastic cells and pseudorosettes. The presence of pseudorosettes was a constant finding, but the number of pseudorosettes varied significantly among cases. All cases displayed focal immunoreactivity for the melanocytic marker HMB45, cathepsin K, and vimentin. Melan A, tyrosinase, cytokeratins, CD10, and microphthalmia transcription factor were each positive in 3 of 4 cases. On ultrastructural examination, numerous electron-dense secretory cytoplasmic granules with some resemblance to melanosomes were identified. The pseudorosettes were composed of reduplicated basement membrane material surrounded by small lymphocyte-like neoplastic cells. Using reverse transcription polymerase chain reaction, 2 tumors were positive for the Alpha-TFEB fusion transcript. The presence of the translocation t(6;11)(Alpha-TFEB) was confirmed in 2 analyzed cases. No von Hippel-Lindau tumor suppressor gene mutation, promotor methylation or loss of heterozygosity of 3p was found. Losses of part of chromosome 1 and chromosome 22 were found in one case.
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