WTP5.02 Two cases of cystic neutrophilic granulomatous mastitis: a breast cancer mimic requiring accurate diagnosis

Introduction Cystic neutrophilic granulomatous mastitis (CNGM) is an uncommon, inflammatory breast condition with distinct histological characteristics often associated with Corynebacterium infection. Between 2001 and 2019, 141 cases have been reported in the literature. Clinically, CNGM may present with features that mimic invasive carcinoma. We report on 2 cases of CNGM presenting to a specialist Breast Unit. Case Reports Case 1 A 37 year old female presented with non-tender, firm right breast swelling superior to the nipple areolar complex. Examination confirmed clinically suspicious, firm, asymmetric nodularity. Ultrasound and mammogram identified a 3.1cm cystic area at the site of clinical concern. Core biopsy suggested CNGM, and subsequent tissue culture identified Corynebacterium species. The patient was treated with a 2-month course of Tetracycline. Case 2 A 39-year-old female with a 2-month history of left nipple retraction, breast tenderness and skin thickening. Examination findings included peau d’orange and firm nodularity between 12 and 3 o’clock positions. Ultrasound and mammogram confirmed a 6.5cm diffuse, mixed solid/cystic area. Enlarged axillary and intramammary nodes were also identified. Core biopsy suggested CNGM, and culture identified Corynebacterium. The patient was treated with a 3-month course of Tetracycline. Clinical and radiological findings were slow to resolve in both cases. Repeat cultures excluded persistent Corynebacterium. Conclusion CNGM can mimic breast cancer, and these cases demonstrate the importance of triangulating clinical, radiological, and histological findings in breast assessment. When CNGM is diagnosed, it is important to assess for Corynebacterium species. CNGM treatment requires prolonged antibiotics, usually beyond resolution of clinical symptoms.