Unusual sonographic appearance of breast cancer metastasis to the pectoralis muscle

Breast cancer is one of the most common malignancies in women. It frequently metastasizes to the lungs, liver, and bone. Breast cancer metastasis to skeletal muscles is rare. Chest wall recurrence in patients that have undergone mastectomy is the most frequent form of local recurrence, and it is generally accompanied by nodules or masses on the chest wall. Here, we describe a case of the unusual appearance of invasive lobular cancer metastasis to the pectoral muscles without discrete nodules or masses in a patient who had undergone mastectomy 12 years ago.