Clinicopathologic, immunohistochemical, molecular cytogenetic profile with treatment and outcomes of 34 cases of Ewing sarcoma with epithelial differentiation, including 6 cases with "Adamantinoma-like" features, diagnosed at a single institution, India.

To analyze clinicopathological features, including treatment profile of 34 cases of Ewing sarcomas with epithelial differentiation, including 6 cases with adamantinoma-like features. EWSR1 gene rearrangement was tested by fluorescence in-situ hybridization. Thirty-four tumors occurred in 19 males and 15 females (M:F = 1.26:1), with age ranging from 7 to 61 years (average = 24.2); in extremities (17), pelvis (5), paraspinal region (6), head and neck region (3), abdomen (2) and lung (1). Prior to molecular testing, 20/34(58.8%) cases were unequivocally diagnosed as Ewing sarcomas. Histopathologically, the most commonly observed pattern was nesting-type, comprising malignant round cells, including adamantinoma-like features, seen in 6 tumors. Immunohistochemically, tumor cells were diffusely positive (cytoplasmic membranous staining) for CD99/MIC2 (34/34), Fli1 (30/30); focally for synaptophysin (4/16) (25%); variably positive for AE1/AE3(31/32)(96.8%), including diffuse immunoexpression in 4 cases; EMA(6/8) and p40(3/8). All 34 (100%) tumors, tested for EWSR1 rearrangement, displayed positive results. According to the treatment details (available in 24/34 cases, 70.5%), most patients (13/24)(54.1%) were treated with surgical resection and a specific chemotherapy(CT) regimen (neoadjuvant or adjuvant settings), including 7 patients, who received adjuvant radiotherapy. During follow-up (16 cases, 47%), 5 patients developed recurrences and 8 developed metastasis, including a single, who developed recurrence. Finally, 10 patients were alive-with-disease (2-22 months); 6 free-of-disease (5-36 months). This constitutes one of the largest documentation of these rare tumors from our subcontinent, which are diagnostically challenging; require molecular confirmation and associated with treatment implications.