A Rare <i>BCOR-</i> ITD Musculoskeletal Sarcoma in an Adult Male Patient

Tumors characterized by <i>BCOR</i> abnormalities occur in diverse body sites and rarely in the bone and soft tissues, in the form of <i>BCOR::CCNB3</i> sarcomas and <i>BCOR</i>-ITD sarcomas, mostly in the pediatric patients. A 35-year-old male patient presented with pain in his right thigh and fullness in his right abdomen. Radiological imaging disclosed a large mass lesion measuring 7 cm × 8.4 cm × 12.3 cm in the right lower abdomen, involving the iliac bone and adjacent muscles. Histopathological examination of the biopsy revealed a tumor comprising oval to spindle cells arranged in interlacing fascicles and focal palisades with interspersed mitotic figures and distinct areas of fibromyxoid stroma exhibiting focal hyalinization in some places. By immunohistochemistry, the tumor cells were diffusely, intensely positive for BCOR, significantly positive for cyclin D1, weakly and patchily for TLE1, and also for SATB2. Furthermore, fluorescence in-situ hybridization for <i>BCOR</i> rearrangement revealed negative results, while comprehensive genetic testing, as well as Sanger sequencing, revealed <i>BCOR</i>-ITD <i>exon 15</i> mutation (inframe_90). This constitutes an extremely rare <i>BCOR</i>-ITD sarcoma, in an adult male patient. The various differential diagnoses and the value of high-throughput molecular testing to uncover these rare tumors are discussed herewith.