[A Case Report of Triple Negative Breast Cancer Diagnosed as Granulomatous Mastitis].

Granulomatous mastitis is a chronic inflammatory disease of unknown causes that forms a breast mass and may be difficult to distinguish from breast cancer on imaging studies. The patient was a woman in her 50's. Needle biopsy was performed for a mass in the upper outer quadrant of the right breast and revealed granulomatous mastitis. Breast magnetic resonance imaging showed that the tumor was malignant. Taking into account that there is a difference between histologic findings and imaging findings and that surgery after steroid therapy for granulomatous mastitis is more likely to cause complications, we decided to perform lumpectomy. The definitive pathological diagnosis was a triple negative, pT1cN0cM0 medullary carcinoma. Postoperative adjuvant chemotherapy was performed. The absence of axillary lymph-node metastasis was confirmed by right axillary sentinel lymph-node biopsy. Radiotherapy was performed on the preserved breast region. Even if granulomatous mastitis is diagnosed, biopsy should be repeated while paying attention to biopsy methods if there is a difference between pathological findings and image findings.