Introduction/Background Breast extramedullary myeloid or granulocytic sarcoma (GS) is a rare tumor. It is considered as a form of acute myeloid leukemia (AML). The clinical and radiographic features of the breast GS are not specific, and therefore the diagnosis can be very challenging.

Methodology We report a case of extramedullary myeloid sarcoma involving the breast treated at the Radiotherapy Oncology department of Habib Bourguiba Hospital in Sfax.

Results A 25-year-old pregnant patient, with AML diagnosed by a bone marrow biopsy. Chemotherapy (CT) was indicated but refused by the patient. She consulted again 3 months after she gave birth with a spinal cord compression. In addition, the patient presented mastodynia. Physical examination revealed painful and tight breasts with no inflammatory signs neither palpable nodules on axillary lymph nodes. Breast ultrasound revealed irregular hypoechoic areas of both breasts suggestive of granulomatous mastitis. The ultrasound examination was graded ACR 4 bilaterally. A complementary breast biopsy concluded to a bilateral GS. The patient was treated according to the adult AML protocol for favorable group. She received 6 cycles of Cytarabine-Idarubicin CT with clinical improvement and complete disappearance of echogenic areas on breast ultrasound. The myelogram showed a complete remission with only 3% of blasts. For the spinal cord compression, the patient underwent palliative radiotherapy at total dose of 20 Gy in 10 fractions and did not report any clinical improvement, she kept a complete paraplegia but with no sign of spinal cord compression.

Conclusion GS of the breast tissue is an extremely rare entity. Providing a correct diagnosis can be challenging for the breast pathology team, since there is not enough data and large prospective studies in the literature. Besides being rare, this tumor closely mimes other neoplasm; it’s therefore important to report local experiences in order to better assist clinicians in their therapeutic management.

Disclosures There are no financial conflicts of interest to disclose.