Myxofibrosarcomas Have Extremely Low Internal Echoes: A Case Report

We report a rare case of myxofibrosarcoma characterized by extremely low internal echoes on ultrasonography, a feature that may serve as an important diagnostic clue. The patient was a 54-year-old woman with a medical history of treatment for primary breast cancer as well as axillary recurrence treatment. After a prolonged disease-free interval of 15 years, the patient detected an ipsilateral axillary mass and was referred to our hospital. Ultrasound revealed a well-circumscribed axillary mass, measuring 21 mm, with extremely low internal echoes. MRI of the axillary mass showed faintly high signals on fat-suppressed T1-weighted images, predominantly high signals on T2-weighted images, and persistent enhancement accompanied by small non-enhanced areas on dynamic studies. Positron emission tomography (PET) showed a maximal standardized uptake value (SUVmax) of 3.1. With a working diagnosis of either axillary re-recurrence or a form of axillary sarcoma, we successfully resected the axillary mass for both diagnostic confirmation and potential curative intent. Postoperative pathological evaluation demonstrated atypical stellate cells with abundant chromatin growing in sparse and focally dense patterns against a mucus-rich background. Immunostaining showed AE1/AE3 negativity and a Ki-67 labeling index of 40%, leading to a final diagnosis of myxofibrosarcoma. Given the patient's preferences and prior exposure to chemotherapy and radiotherapy for breast cancer, she did not receive any adjuvant therapy and has been followed without recurrence on an outpatient basis for 11 months. Diagnostic physicians should be aware that myxofibrosarcomas may exhibit extremely low internal echoes, weak high signals on fat-suppressed T1-weighted images, and low SUVmax values on PET, findings that are attributable to the mucus-rich background.