A Challenging Case of Myeloid Sarcoma Misdiagnosed as High-Grade B-Cell Lymphoma

A 46-year-old female presented with back pain associated with progressive bilateral lower extremity weakness and paresthesia. Imaging studies revealed a retroperitoneal mass with severe spinal compression. Histological sections showed blastoid cells with large nuclei, irregular membranes, fine chromatin, and prominent nucleoli. Immunohistochemical stains (IHC) showed neoplastic cells positive for B-cell markers. This patient was diagnosed with a high-grade B-cell lymphoma before transferred to our institution for further work-up. After review of the case, additional IHC was requested which revealed positivity for CD117 and myeloperoxidase (MPO). The overall morphological and immunophenotypical features were most compatible with myeloid sarcoma with aberrant expression of B-cell markers and this patient's diagnosis was amended. A literature review showed that 40-50% of myeloid sarcomas are misdiagnosed as lymphoma since they can frequently stain with B-cell or T-cell markers, which makes it challenging for an accurate diagnosis and sub-classification. We present this case to raise awareness of the potential diagnostic pitfalls.