It's Not Always Gynecomastia: A Case of Diffuse Large B-Cell Lymphoma Presenting as Breast Mass in a Male Patient.

We report a case of diffuse large B-cell breast lymphoma that presented as a palpable breast lump in a male patient evaluated with digital mammography and targeted breast ultrasound (US) but ultimately confirmed by US-guided core needle biopsy. We will discuss the appropriate workup algorithm for a palpable breast lump in a male patient as outlined by the American College of Radiology (ACR) Appropriateness Criteria. While gynecomastia is the most common reason for a new palpable breast lump in a male patient, male breast cancer (including lymphoma and metastasis) can have a similar appearance on imaging. Our goal is to provide clarity on proper radiographic assessment protocols and imaging features of palpable breast masses in men by emphasizing the role of anatomical location and symmetry in distinguishing it from more common causes, such as gynecomastia, in future diagnostic imaging scenarios.