Xanthogranulomatous reaction to a ruptured galactocele.

We describe a case of a 34-year-old, healthy, lactating female with a 2-month history of breast pain and an enlarging, tender mass on her right nipple. Her right breast was firm and mildly engorged without mass, warmth or erythema. A tender, yellow nodule was located on the superior aspect of the nipple, obstructing the flow of milk from this portion of the nipple. A biopsy showed epidermal erosion, sheets of cells with massively distended, foamy cytoplasm in the dermis, and a hypertrophied and occluded glandular duct, consistent with reactive squamous metaplasia. Immunostaining for CD68 confirmed the foamy cells were macrophages, and anti-human milk fat globulin-1 (HMFG1) labeled the substance within the macrophages consistent with human breast milk. Therefore, the lesion could be identified as a xanthogranulomatous reaction to a ruptured galactocele.