Case report describes myeloid sarcoma relapse in breast after nasal cavity presentation

Myeloid sarcoma (MS) is a rare extramedullary manifestation of acute myeloid leukemia. While MS can involve various organs, isolated involvement of the nasal cavity or breast is uncommon, and the sequential involvement of both sites in a single patient is extremely rare. We present the case of a 68-year-old female who developed an MS relapse in the right breast 6 years after being treated for primary MS of the right nasal cavity. In 2018, she presented with a right nasal mass, initially suspected clinically to be a polyp. Histopathological and immunohistochemical (IHC) analyses confirmed MS. She achieved complete remission following localized radiotherapy and cytarabine-based systemic chemotherapy. After a six-year disease-free interval, she presented in 2025 with a painful right breast nodule. Initial imaging indicated a primary breast malignancy (BI-RADS 4B). However, postoperative IHC analysis, demonstrating myeloperoxidase (MPO) positivity, confirmed an extramedullary relapse of MS. The patient was subsequently treated with further chemotherapy and hypofractionated radiotherapy. This case highlights that extramedullary MS can perfectly mimic primary solid tumors both clinically and morphologically. It emphasizes the critical role of a comprehensive immunohistochemical panel, particularly the inclusion of myeloid-specific markers, in differentiating MS from poorly differentiated carcinomas. Such pathological vigilance is indispensable for avoiding catastrophic diagnostic pitfalls and preventing inappropriate surgical interventions in patients presenting with atypical extramedullary masses.