A rare case of nodular mucinosis of the breast away from the nipple‐areola complex

Abstract

A 40‐year‐old Chinese woman with no significant medical history presented with a right breast lump of 2‐year duration. It has been gradually increasing in size and painful during menstruation. She did not notice any breast skin changes or nipple discharge. She has three children, breastfed all of them, and has never taken any hormone‐ containing medication. On examination, there was a small soft, mo‐ bile lump at 1‐2 o clock of the right breast. Examination of the rest of the right breast and the nipple‐areola complex was unremarkable. Mammography did not reveal any circumscribed lesion or microcal‐ cifications (Figure 1). Ultrasonography of the right breast revealed a 1.1 × 1.1 × 0.7 cm, lobulated, circumscribed nodule at 2 o clock, 7.1 cm from the nipple (Figure 2). It was indeterminate for fibroad‐ enoma or mass (BI‐RADS 4). Ultrasound‐guided core biopsy of the nodule revealed a low‐grade fibromyxoid stromal proliferation. As the histologic features were not definitive, with both neoplastic and non‐neoplastic diagnoses possible, decision was made to carry out excision biopsy. Patient subsequently underwent hookwire‐guided excision biopsy of the lesion. Grossly, the specimen is a 1 × 1 × 1 cm myxoid nodule with punctate calcification. All resection margins are clear, and the rest of breast tissue shows stromal fibrosis and adenosis. There is no ev‐ idence of malignancy. Histopathologically, the sections show a cir‐ cumscribed nodular lesion consisting mainly of myxoid stroma with scattered bland spindle cells and elongated thin‐walled blood ves‐ sels (Figure 3A,B). A few entrapped mammary ducts and stroma are present at the periphery (Figure 3C). No high‐grade nuclear atypia or increased mitosis is seen. The myxoid stroma is negative for PAS (periodic acid‐Schiff) and positive for Alcian blue (Figure 3D). The overall features are compatible with nodular mucinosis of the breast (NMB). Postoperatively, patient recovered well and has been followed up regularly in outpatient clinic, with no signs of recurrence.