An unusual breast lump: osseous metaplasia

We present a rare case of osseous metaplasia in the breast with no other associated breast pathology. A 46-year-old HIV-positive lady presented to the breast clinic with new onset intermittent left-sided mastalgia. Clinical examination revealed an indeterminate mass in the left breast with palpable left axillary lymphadenopathy. Mammography and ultrasonography were suggestive of a possible malignancy, with the latter also detecting the presence of abnormal nodes in the axilla. An ultrasound-guided core biopsy of the breast lesion showed only hyalinised normal breast tissue on two occasions. Owing to the diagnostic uncertainty, the patient underwent a wire-guided excision biopsy of the breast lesion, with the final histology demonstrating bone matrix deposition with viable osteocytes within lacunae and associated osteoclasts with spindle cells, consistent with osseous metaplasia. A core biopsy of the axillary lymph nodes was normal. The patient was therefore reassured and discharged from the clinic.