Primary sclerosing epithelioid fibrosarcoma of kidney with variant histomorphologic features: report of 2 cases and review of the literature

The authors present two cases of primary sclerosing epithelioid fibrosarcoma (SEF) of the kidney. Both patients had a mass in the upper part of the left kidney without any primary extrarenal neoplastic lesions. Grossly, the tumors were solid masses both measuring 7.5 cm in the greatest diameter. Histologically, one of the lesions exhibited a predominantly lobular growth of round or oval small uniform epithelioid cells in variable cellularity. Circular zones of crowded tumor cells alternating with hypocellular collagenous tissue in a concentric fashion around entrapped native renal tubules were distinctive. The second case was distinctive with significant cytological atypia in the neoplastic cells and prominent reactive proliferations in the trapped renal tubules. Immunohistochemically, vimentin, bcl-2 and MUC4 were diffusely positive in both. They were negative for S-100 protein, CD34, and desmin, whereas CD99 were positive in one lesion. Fluorescence in situ hybridization assay using dual staining probes detected EWSR1-CREB3L1 fusion in each lesion, which is characteristic molecular findings of SEF. One patient presented widespread distant metastases at the time of diagnosis. In the other, no tumor deposits were detected other than primary. Both patients have been alive with 30 and 10 month follow-ups, respectively. These tumors are 6th and 7th cases of primary renal SEF in the literature confirmed by FISH study, which exhibit unique and remarkable histomorphologic features.