Rare cytogenetic subtype in a case of Ewing sarcoma with diagnostic dilemma: A case report

Ewing sarcoma is aggressive tumor with round cell morphology and very common in <15 years of age and young adults. Overall, incidence ranges from 10 to 15% of all the bone sarcomas. Ewing sarcoma most commonly affects lower extremity especially femur and other sites includes pelvis, upper extremity, and axial skeleton and ribs. The tumor cells are round blue cells on routine microscopy and the close differential includes other soft-tissue tumors such as primitive neuroectodermal tumor and neuroepithelioma. In addition to histology, the ancillary tests such as immunohistochemistry and cytogenetics studies are important for confirm diagnosis. Ewing sarcoma characteristically shows involvement of EWS gene located on chromosome 22q12. The most frequent translocation is EWS::FLI1 [t(11;22)(q24;q12) which appears approximately 85% of the cases followed by rare subtypes. Here, we report a case of young male who presented with fever, low backache, and weakness in lower limbs since 20 days. On CBC profile was normal and no significant past history; radiologically, there was mild-to-moderate compression fracture of L4 vertebral body with associated mild-to-moderate retropulsion of the posterior portion directly indenting and compressing the descending intrathecal nerve roots on both sides with small to moderate sized adjacent soft-tissue component. Diffuse alteration of marrow signal intensity involving cervical, dorsal, lumbar, and sacral vertebral bodies s/o? leukemia/lymphoma. Bone marrow and trephine biopsy suggested non hematopoietic malignancy. Cytogenetics studies showed aneuploidy (48,XY,+4,+8,t[9;22;21]); on that basis considered myeloid neoplasm with BCR:: ABL1 fusion. Which further on fluorescent in situ hybridization (FISH) considered negative. The final diagnosis was favored Ewing’ sarcoma based on the immunohistochemistry and cytogenetic translocation of chromosome 21 and 22. We report this case to highlight the importance of FISH as well as conventional karyotype for the additional chromosomal abnormalities in the Ewing’ sarcoma which, in isolation, leads to diagnostic dilemma.