Primary diffuse large B-cell lymphoma of the breast.

Diffuse large B cell lymphoma (DLBL) of the breast is a rare subtype of breast tumor, the diagnosis of which is based on the cytological and histopathological features of this unique neoplasm. A 28-year-old woman noticed a mass in her right breast. It could not be definitely diagnosed clinically by diagnostic imaging (mammography, ultrasonography), so malignant tumor not otherwise specified was diagnosed. Fine-needle aspiration cytology (FNAC) suggested that it was malignant lymphoma; however it was difficult to distinguish from reactive lymphocytes. Excisional biopsy of the breast mass suggested malignant lymphoma. Based on the diagnosis of malignant lymphoma by FNAC and excisional biopsy, lumpectomy was performed and DLBL was diagnosed histologically according to the World Health Organization classification. DLBL is difficult to distinguish from other types of malignant lymphoma by routine immunohistochemical evaluation. Some previous studies have showed that the octamer-binding transcription factor 2 (Oct2) and coactivator B-cell Oct-binding protein 1 (BOB.1) and the pan-B-cell markers CD20 and CD79a may aid in the diagnosis of malignant lymphoma. In our case, the staining of large atypical lymphocytes for CD20, CD79a, BOB.1 and Oct2 was strongly positive and supports the notion that BOB.1 and Oct2 are also useful immunohistochemical markers for DLBL of the breast.