Myeloid sarcoma: A 7-year retrospective study from a tertiary cancer care center, illustrating the clinical, morphological, and immunohistochemical features

Objectives Myeloid sarcoma (MS) is a tumor mass formed by the collection of myeloid blasts at sites other than bone marrow. MS can occur as an isolated mass or concurrently as acute myeloid leukemia (AML) in bone marrow or in a case of myeloproliferative neoplasm/myelodysplastic neoplasm. The aim of the study was to highlight the varied presentation and morpho-immunohistochemistry guide to recognize this entity in biopsy for its therapeutic connotation. Material and Methods The present study is a retrospective analysis; cases diagnosed as MS between 2014 and 2021 were included in the study. Clinicopathological details like age, gender, site of biopsy, bone marrow status, histopathology, immunohistochemistry, treatment, and follow-up information, where available, were included. Results A total of 24 cases were diagnosed with the age range of 2–67 years (Mean 32.08 ± 17.38 years), male: female ratio was 1.1:1. The sites at presentation were: spinal/paraspinal region, lymph nodes, breast, cervix, orbit, nasal cavity/nasopharynx, skin, mediastinum, cheek swelling, central nervous system, and chest wall. De novo MS was present in seven cases (29%), while concurrent AML in peripheral blood /bone marrow was noted in six cases (25%). Histopathological analysis revealed three morphological types: differentiated, monocytic, and undifferentiated. IHC done in 22 cases showed positive for Leucocyte common antigen (LCA) (14/18), MPO (16/22), CD117 (20/22), CD34 (12/22), CD56 (5/10), and CD68 (4/11). Molecular markers that were positive were RUNX1::RUNX1T1, NPM1, and BCR::ABL1 in three, two, and two cases, respectively. Conclusion The present case series showcases the common and uncommon clinical presentation of MS cases. The varied sites of involvement, non-diagnostic radiological features, and undifferentiated morphology make diagnosis a challenge. The authors suggest in tandem use of broad IHC panel, flow cytometry, and molecular studies for arriving at the right diagnosis.