Rare case of dedifferentiated liposarcoma of the pectoralis major muscle found on screening mammography

Liposarcoma of the pectoralis major muscle is exceedingly rare, with less than 10 cases reported in the literature. Dedifferentiated liposarcoma of the pectoralis major is rarer still, with only 2 reported cases. It is particularly important to be able to accurately diagnose dedifferentiated liposarcoma, as it has a much poorer prognosis than well-differentiated liposarcoma and requires different treatment regimens. Percutaneous biopsy is shown to not be helpful in identifying dedifferentiation. However, there are imaging clues that the radiologist can use to identify dedifferentiation and guide the treating surgeons and oncologists. In this report, we describe a case of dedifferentiated liposarcoma of the left pectoralis major muscle found on screening mammography of the left breast.