The Rare Isolated Solitary Muscle Metastasis of Breast Carcinoma Confirmed by 18F-FDG PET/CT

Muscle metastasis of breast carcinoma is a rare condition. It often coexists with other organ metastases. A mass in the left sternocleidomastoid muscle was detected 1 year after diagnosis in a 51-year-old patient with locally advanced invasive ductal breast carcinoma. Although biopsy from this lesion was applied two times, the malignancy was not found. However, the patient had clinically-suspected metastasis. The 18F-FDG PET/CT was performed for restaging. The tru-cut biopsy from the hypermetabolic area in muscle mass proved the metastasis contained osteoclast giant cell carcinoma of the breast. Our patient is the first case in the literature of the diagnosis of breast cancer with initial solitary metastasis to the sternocleidomastoid muscle.