Key Clinical Message: Primary breast MALT lymphoma is an extremely rare and indolent malignancy with favorable outcomes. This case report aims to report typical imaging and pathologic findings to improve understanding and awareness of the presentation, diagnosis, and management of this uncommon entity.IntroductionPrimary breast lymphomas (PBL) are uncommon, having been reported to represent up to 1% of all cases of non-Hodgkin lymphoma [1,3] and only 0.4-1% of all breast malignancies [2,3]. Mucosa-associated lymphoid tissue (MALT) lymphoma is an extranodal B-cell lymphoma and a subtype of marginal zone lymphoma (MZL), which is a classically indolent form of non-Hodgkin’s lymphoma (NHL) with an average age of presentation above 65 years of age with a slight female predilection. MALT lymphomas are more commonly associated with mucosal sites such as the gastrointestinal tract, lungs, and salivary glands, with the stomach being the most frequent extranodal site. As such, primary involvement of the breast is extremely unusual, only accounting for up to 9% of primary breast lymphomas and therefore fewer than 0.1% of all breast malignancies [4]. The clinical presentation of primary breast MALT lymphoma can be subtle, often manifesting asymptomatically as a painless, palpable mass. Due to its rarity and nonspecific presentation on mammography, this entity may not be considered in the initial differential, potentially leading to delays in diagnosis.Case HistoryThe patient is a 65-year-old female with no significant past medical history who presented to her primary care physician for routine healthcare maintenance. No concerning breast symptoms were identified, with the patient denying breast pain, nipple discharge, or palpable mass. She had no personal history of breast or ovarian cancer, no family history of breast cancer, with a low lifetime Tyrer-Cuzick score of 12%. Given her age, she underwent routine screening mammography, with identification of a new asymmetry in the anterior lateral left breast. This was categorized as BI-RADS 0 and callback for diagnostic mammography was performed. On diagnostic mammogram, the asymmetry persisted on spot compression views (Figure 1A-B), although no sonographic correlate was definitively identified. This was classified as BI-RADS 4, with a recommendation for tissue sampling.

IntroductionMultiple similarities in the embryogenic epithelial-myoepithelial cell differentiation of the salivary glands and breast tissue allows for overlap of neoplastic development of classically salivary gland tumors in the breast. While biphasic epithelial-myoepithelial lesions of the breast are uncommon and include pleomorphic adenoma, adenoid cystic carcinoma, and benign adenomyoepithelioma, malignant transformation of benign adenomyoepithelioma into epithelial-myoepithelial carcinoma of the breast is extremely rare, with fewer than 50 reported cases in the existing literature over the past four decades [1,2]. Thus far, there have previously been no cases that bring up the possibility of EMC development following the treatment of primary breast cancer in the existing literature.