BCOR overexpression in pediatric sarcomas- a morphologic continuum of mixed round and spindle cell tumors

The vast majority of BCOR (BCL6 corepressor) sarcomas occur in the pediatric population and include different clinico-pathologic entities. This study evaluates morphology, immunohistochemistry and clinical outcome in pediatric BCOR sarcomas. Children, aged ≤ 18yrs, diagnosed to have translocation negative Ewing-like sarcoma, clear cell sarcoma of the kidney and primitive myxoid mesenchymal tumor of infancy, over a period of five years were included. Immunohistochemical staining for BCOR antibody was done and the cases with BCOR overexpression were subjected to a further immunopanel comprising of special AT-rich sequence-binding protein 2 (SATB2), Transducin-Like enhancer of split-1 (TLE1), Cyclin D1 and NKX2.2. The clinical outcome of patients with BCOR overexpression was assessed. BCOR overexpression was seen in 16/42 cases; Five were primary soft tissue tumors, three were primary bone tumors, seven were clear cell sarcoma of the kidney and one primary renal sarcoma. The median age of this group was 3.5 years (range 2–18 years) with male predominance (75%). All the BCOR positive tumors showed statistically significant morphological and immunohistochemical overlap. 4/16 did not take treatment at our center. Of the 12 who received treatment, 8 are in Complete Remission 1 (CR1). The mean event-free survival (EFS) and overall survival (OS) were 51.89 months (95% CI: 37.36-66.42) and 62.08 months (95% confidence interval (CI): 52.85-71.30) respectively. BCOR sarcomas did not show any statistically significant histological and immunohistochemical differences, thus reiterating the morphologic continuum of these clinically distinct tumors.