Mucosa-associated lymphoid tissue lymphoma of the breast: bilateral metachronous presentation

Primary breast lymphoma is a rare clinical entity accounting for less than 0.5% of all breast malignancies [1]. By far, the most common histology observed in primary breast lymphoma is diffuse large B-cell lymphoma, which accounts for 53–73% of cases in large primary breast lymphoma series [2–4]. Extranodal marginal zone B-cell lymphoma, or mucosa-associated lymphoid tissue (MALT) lymphoma, makes up only *9% of primary breast lymphomas [5]. Conversely, only 1–3% of localized extranodal MALT lymphomas arise from the breasts [6–9]. An interesting finding observed by Tsang et al. from Princess Margaret Hospital in a study of 103 cases of localized MALT lymphoma was a predilection for relapses to occur in contralateral paired organs, which was observed in one-third of orbital adnexa and salivary gland MALT lymphoma recurrences [8]. This finding may be related to presence of ‘homing receptors’ in malignant lymphocytes, which are postulated to mediate the pattern of tissuespecific disease dissemination that is observed in intestinal MALT lymphoma and several other hematologic malignancies, including cutaneous lymphoma and multiple myeloma [10]. However, it is unclear if this propensity for tissue-specific involvement also extends to MALT lymphomas arising in the breast. There have been a number of case reports of patients presenting with synchronous bilateral primary breast MALT lymphoma [11–14]. Here, we report a case of a stage IAE MALT lymphoma of the breast, with isolated relapse in the contralateral breast 3 years after local therapy. A 57-year-old woman presented with a palpable, non-tender, pea-sized mass in the lower inner quadrant of her right breast. A diagnostic mammogram was performed, which showed a 1.4 cm nodule in the inferior, medial aspect of the right breast with irregular margins. A targeted ultrasound of this nodule revealed a 1.3 cm hypoechoic mass with lobulated margins. An ultrasound-guided core needle biopsy of this lesion was performed. Histopathology and immunohistochemistry were consistent with marginal zone B-cell lymphoma. The patient underwent staging with positron emission tomography/ computed tomography scanning and a bone marrow biopsy, both of which were negative for extramammary disease involvement. The patient was therefore classified as stage IAE, and received definitive radiation therapy to the right whole breast consisting of 30 Gy in 15 fractions utilizing opposed tangent fields. After the radiation therapy, the patient had complete resolution of her breast mass both clinically and radiographically. She remained in good health for approximately the next 3 years, when a routine screening mammogram revealed an infiltrative process with a finely reticulated pattern in the upper medial aspect of her left breast. This pattern was felt to be similar in appearance to the nodule seen in her right breast during her initial presentation. There were no palpable abnormalities clinically. An ultrasound of the left breast showed a hyperechoic pattern in the fatty tissue extending at least 3 cm. An ultrasound guided biopsy of this lesion revealed