Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 56 3 2018 03 06 204 207 EN Fariba Binesh Department of Pathology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Hassan Ali Vahedian Department of Oncology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Masoud Shabani Department of Radiology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Saeedeh Zare Department of Radiology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. Seyed Hossein Shahcheraghi Department of Modern Sciences and Technologies, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. AND Infectious Diseases Research Center, Shahid Sadoughi University of Medical Sciences, Yazd, Iran. 2016 11 26 2017 04 16 Breast plasmacytoma is a rare neoplasm. Here we present a case of extramedullary plasmacytoma of the breast in a 41-year-old Iranian lady who was a known case of spine plasmacytoma. Two years ago study case was presented with severe back pain. At that time, MRI revealed an expansile and destructive lesion in the body of S1 which was suggestive of metastasis. The patient underwent incisional biopsy that was a representative of a plasmacytoma. Skeletal survey, bone marrow aspiration, and serum protein electrophoresis were negative. The patient received radiation therapy. This year (2 years later) she detected a mass in her right breast. A mammography revealed a 30 mm high-density mass with an ill-defined border in the right breast. The mass was excised, and histological examination confirmed the diagnosis of plasmacytoma. Although plasmacytoma of the breast is rare, this tumor should be considered as a differential diagnosis of a breast mass, especially in patients with plasma cell dyscrasias. https://acta.tums.ac.ir/index.php/acta/article/view/6035 https://acta.tums.ac.ir/index.php/acta/article/download/6035/5069