Multiple Primary Malignant Neoplasms: A Case Report of Breast Mucinous Carcinoma and Extramammary Diffuse Large B-Cell Lymphoma in a Male Patient

Multiple primary malignant neoplasms refer to two or more malignancies in an individual that are not related. We report a case of a 78-year-old male with concurrent breast mucinous carcinoma and extramammary lymphoma. The patient initially presented with palpable masses in the left breast and the right groin, which were pathologically confirmed after a surgical biopsy as breast mucinous carcinoma and diffuse large B-cell lymphoma, respectively. He underwent whole-body 18-fluorine deoxyglucose PET/CT before surgery, and an enhancing nodular lesion in the left lingual tonsil was found incidentally. It was later confirmed as a diffuse large B-cell lymphoma, a pathology of the same type as the right inguinal mass. Unspecified lymphadenopathies in breast cancer patients may easily be considered as metastatic lesions. However, this case suggests that lymphomas should be included in the differential diagnoses to avoid misdiagnosis and treatment delay, especially in older adult patients.