BCOR and endometrioid stromal sarcoma: BCOR in-frame internal tandem duplications in exon 15 and BCOR-CCNB3/BCOR-MAML1 gene fusion are regarded as specific molecular and key tumor driving event in a subtype of bone sarcoma, clear cell sarcomas of the kidney (CCSK), primitive myxoid mesenchymal tumor of infancy (PMMT), and in endometrial stromal sarcomas [4, 5, 12, 15].