A Case of Breast Cancer with Polyostotic Fibrous Dysplasia that was Indistinguishable from Multiple Bone Metastases

Abstract

A 49-year-old woman visited our hospital after noticing that a lump in her left breast had recently begun to grow. The lump was first noticed 10 years previously. A tumor with a maximum diameter of 6 cm was palpated in the lower outer quadrant of the left breast without lymph node swelling in the left axilla. Ultrasonography showed an intracystic tumor with a sessile solid part. A core needle biopsy was performed, and a diagnosis of ductal carcinoma and mucinous carcinoma was made. A bone scintigraphy revealed abnormal accumulation in multiple bone lesions, and multiple bone metastases were highly suspected. However, it was considered that most of the breast tumor was situated within the cyst, and a bone computed tomography (CT) scan did not show typical findings of bone metastasis. Additional CT and magnetic resonance imaging scans revealed that the multiple bone lesions were consistent with polyostotic fibrous dysplasia. The patient was therefore diagnosed with early breast cancer, and underwent a left mastectomy and sentinel lymph node biopsy. Since fibrous dysplasia of bone shows similar findings to that of bone metastasis detected by bone scintigraphy, distinction between the two is critical for managing patients with breast cancer.