EZR-ROS1 fusion renal cell carcinoma mimicking urothelial carcinoma: report of a previously undescribed gene fusion in renal cell carcinoma.

A subset of renal cell carcinomas harbor gene fusions, and we report the first case of an EZR-ROS1 fusion in renal cell carcinoma. A 47-year-old female presented with hematuria and a mass involving the renal pelvis. Renal biopsy revealed a tumor with solid and tubular architecture that was diffusely positive for PAX8, CK7, and vimentin; retained expression of INI1; focally positive for P504S; and negative for GATA3 and TFE3. Partial nephrectomy was performed, and histologically, the tumor had solid and tubular architecture with mucin-like content within tubules. The nuclei corresponded to WHO/ISUP grade 2 and 3. The morphology was neither specific nor diagnostic, and a final diagnosis of unclassified renal cell carcinoma with solid and tubular architecture was rendered. Molecular sequencing revealed an EZR-ROS1 fusion: a fusion that has never been reported in renal cell carcinoma. Recognition of this fusion is of significance if the tumor becomes metastatic as treatment with crizotinib may be considered.