The Breast Mass That Wasn't Cancer

A 33-year-old woman presents to the breast surgery clinic with a 6-week history of a progressively enlarging, painful left breast mass. She notes overlying skin erythema that has worsened despite two courses of oral cephalexin prescribed by her primary care physician. She has no fever, nipple discharge, or axillary lymphadenopathy. She has no history of breast trauma or prior breast surgery. She stopped breastfeeding her youngest child 18 months ago.

She has no significant past medical history and takes no immunosuppressive medications. She is a non-smoker. A mammogram performed 2 weeks ago was read as BI-RADS 4 (suspicious), prompting a core needle biopsy.

On examination the left breast has a firm, tender, ill-defined 4 × 5 cm mass in the periareolar region with overlying violaceous skin changes. There is no fluctuance, no nipple retraction, and no palpable axillary lymphadenopathy. The right breast is unremarkable.

The core biopsy returns showing non-caseating granulomatous inflammation with lipogranulomas containing cystic spaces surrounded by neutrophils. No malignant cells are identified. Acid-fast and fungal stains are negative. Standard aerobic cultures show no growth at 48 hours. The pathologist notes the histologic pattern is consistent with cystic neutrophilic granulomatous mastitis (CNGM).