J Pathol Transl Med.  2023 Sep;57(5):284-288. 10.4132/jptm.2023.08.08.

EWSR1 rearranged primary renal myoepithelial carcinoma: a diagnostic conundrum

  • 1Department of Onco-Pathology, Mahamana Pandit Madan Mohan Malviya Cancer Centre, Varanasi, India


Primary renal myoepithelial carcinoma is an exceedingly rare neoplasm with an aggressive phenotype and Ewing sarcoma breakpoint region 1 (EWSR1) rearrangement in a small fraction of cases. In addition to its rarity, the diagnosis can be challenging for the pathologist due to morphologic heterogeneity, particularly on the biopsy specimen. At times, immunohistochemistry may be indecisive; therefore, molecular studies should be undertaken for clinching the diagnosis. We aim to illustrate a case of primary myoepithelial carcinoma of the kidney with EWSR1-rearrangement in a 67-year-old male patient who presented with right supraclavicular mass, which was clinically diagnosed as carcinoma of an unknown primary. An elaborate immunohistochemical work-up aided by fluorescent in-situ hybridization allowed us to reach a conclusive diagnosis. This unusual case report advocates that one should be aware of the histological mimickers and begin with broad differential diagnoses alongside sporadic ones and then narrow them down with appropriate ancillary studies.


EWSR1 gene rearrangement; Kidney; Myoepithelial carcinoma; Prognosis


  • Fig. 1. The neoplastic cells are arranged in cords, trabeculae, tubules and scattered singly over a loose myxoid stroma (A). The neoplastic cells are oval to spindle-shaped and possess largely monomorphic nuclei, dispersed chromatin, inconspicuous nucleoli, and a scant to moderate amount of eosinophilic cytoplasm (B). The neoplastic cells are positive for AE1/AE3 (C) and smooth muscle actin (D).

  • Fig. 2. Positron emission tomography and computed tomography (PET-CT) images of the hypermetabolic right supraclavicular mass (A, B). PET-CT images of the left renal lesion (C, D).

  • Fig. 3. The tumor cells are disposed in nests and sheets (A). The tumor cells are round, with a high nucleo-cytoplasmic ratio, fine to vesicular nuclei, prominent nucleoli, and scant cytoplasm (B). The tumor cells are positive for AE1/AE3 (C), CD10 (D), smooth muscle actin (E), and p63 (F).

  • Fig. 4. Fluorescent in-situ hybridization using dual-color breakapart probe illustrating Ewing sarcoma breakpoint region 1 (EWSR1) gene rearrangement. The pink arrows indicate separated (split) red and green signals denoting a rearrangement involving the EWSR1 gene at 22q12. The white arrow points toward a normal fused signal, which is the site of the EWSR1 gene.



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