When it is not cancer: Cystic neutrophilic granulomatous mastitis masquerading as carcinoma

Cystic neutrophilic granulomatous mastitis (CNGM) is a rare inflammatory breast disease that can clinically and radiologically mimic breast carcinoma. Accurate histological diagnosis is essential to prevent unnecessary treatment and guide appropriate therapeutic management. A 33-year-old female patient presented with a painful, firm nodule in the left breast, in the absence of typical inflammatory clinical findings. Breast ultrasound revealed an ill-defined, hypoechoic nodule measuring 17mm×22mm, with peripheral acoustic shadowing, classified as BI-RADS 4B. A core needle biopsy was performed. Histopathological examination with haematoxylin and eosin (H&E) staining demonstrated granulomatous inflammation with characteristic pseudocystic spaces rimmed by numerous neutrophils. The patient was managed conservatively, resulting in symptomatic improvement. This case underscores the diagnostic challenge of distinguishing CNGM from breast carcinoma. Clinicopathological correlation is crucial, as specific histological features are key to avoiding overtreatment. Raising awareness of this entity among clinicians and pathologists can optimise patient management and reduce unnecessary surgical interventions.