Primary Ewing sarcoma of the kidney: A series of four cases.

Ewing sarcoma (ES), the neuroectodermal derived tumour typically occurs in the bone and soft tissue of children and young adults. Primary ES of the kidney is strikingly rare and only a few cases and small case series have been documented. Due to the highly aggressive nature of this neoplasm, distinction from other morphological mimickers is truly indispensable in terms of treatment and prognosis. Here we describe the clinicopathological features of four cases of primary ES of the kidney with special emphasis on one case having extensive neural differentiation postneo- adjuvant chemotherapy (NACT). Extensive neural differentiation in renal ES has not been documented to date.Four patients (age range from 15-35 years) had kidney mass and multiple distant metastases at first presentation. Primary diagnosis of Ewing sarcoma was rendered by histopathology with the help of immunohistochemistry on core biopsy material. Tumour cells in all cases showed diffuse membranous CD99, nuclear FLI-1 and NKX2.2. Two of the patients had undergone radical nephrectomy followed by combination chemotherapy. Another two patients were first treated with neo-adjuvant chemotherapy (NACT) followed by radical nephrectomy. In one of them, histopathological examination of nephrectomy specimens revealed extensive neural differentiation. The adrenal gland was free in all four cases. The follow-up period was 12 -24 months. Three patients had survived and one of them became disease-free.Primary ES of the kidney is a rare and lethal entity. Due to overwhelming rarity, chemotherapy protocol has not been standardised and followed as ES in bone/soft tissue. Histopathological confirmation and prompt initiation of treatment may improve patient survival and outcome.