A breast cancer look-alike in primary care: Diagnosing idiopathic granulomatous mastitis

A BSTRACT Idiopathic granulomatous mastitis (IGM) is a rare benign inflammatory condition that can closely mimic breast cancer on clinical examination and imaging studies, creating diagnostic challenges for primary care providers who serve as the initial point of contact for breast complaints. We present the case of a 33-year-old woman with a strong family history of breast cancer who developed a 10 cm left breast mass associated with cyclic pain. Despite a normal mammogram five months prior, imaging workup including mammography, ultrasound, and MRI revealed findings highly suspicious for malignancy, with the MRI demonstrating diffuse asymmetric nonmass enhancement and abnormal axillary lymphadenopathy, resulting in a BI-RADS 4 classification. Ultrasound-guided biopsy of both the breast mass and axillary lymph node revealed noncaseating granulomatous inflammation without evidence of malignancy, confirming the diagnosis of IGM. The patient’s mass resolved spontaneously within weeks without intervention. This case highlights the importance of primary care providers recognizing IGM in the differential diagnosis of breast masses in reproductive-aged women. While thorough evaluation including tissue sampling remains essential to exclude malignancy, increased awareness of this benign condition that can masquerade as breast cancer can help guide clinical decision-making and patient counseling, especially for patients with heightened anxiety due to family history.