Myeloid Sarcoma: A Series of Five Cases from a Tertiary Care Centre in Tamil Nadu, India

Myeloid Sarcoma (MS) constitutes a rare extramedullary manifestation characterised by the clonal proliferation of myeloid precursor cells. It may present in association with Acute Myeloid Leukaemia (AML), Myelodysplastic Syndromes (MDS), or Myeloproliferative Neoplasms (MPN), or as an isolated entity. Its variable morphology and frequent absence of a prior haematological history present a significant diagnostic challenge. This report delineates five cases of MS diagnosed at our tertiary care centre between July 2023 and June 2025. All patients were male, with a median age of 36 years. Affected anatomical sites included soft tissue (n=2), bone (n=1), lymph node (n=1), and testis (n=1). Two patients had an underlying diagnosis of Chronic Myeloid Leukaemia (CML). Histopathological evaluation consistently revealed blastic morphology, often closely mimicking lymphoma or small round cell tumours. Immunohistochemistry (IHC) proved indispensable for definitive diagnosis, with all cases demonstrating positivity for CD34 and Myeloperoxidase (MPO). Notably, one case also exhibited CD99 and FLI-1 expression, thereby creating diagnostic overlap with Ewing sarcoma. This case series highlights the diverse presentations and inherent diagnostic pitfalls of MS, emphasising the importance of considering MS in the differential diagnosis of extramedullary masses and employing judicious IHC, particularly MPO and CD34, to ensure accurate diagnosis.