Abstract. Granulocytic sarcoma (GS) is an unusual type of tumor composed of immature cells outside the bone marrow. The disease exhibits a correlation with acute myeloid leukemia and other myeloproliferative disorders. Although it can invade a number of areas of the body, the involvement of the breast is uncommon. The present study reports the case of a 58-year-old female with a mildly tender lump in the left breast that had been apparent for one year. Available diagnostic techniques, including ultrasound, magnetic resonance imaging and mammography, were systematically used to determine a diagnosis of GS, and lumpectomy and systemic chemotherapy were performed. The patient was satisfied with the result of no local recurrence at the one year follow-up examination. The present study discusses the clinical and pathological characteristics of the present case of GC.