Double Diagnostic Dilemma in Metaplastic Breast Carcinoma

Metaplastic breast carcinoma is a rare and aggressive subtype of breast cancer. It is characterized by the differentiation of epithelial cells into mesenchymal components and often presents as a triple-negative phenotype. Its varied histomorphology can resemble sarcoma or lymphoma, making diagnosis difficult. We will be discussing a case of a 50-year-old woman with a right breast mass and multiple fluorodeoxyglucose (FDG)-avid splenic lesions on PET/CT, which initially suggested a metastatic disease or a disseminated lymphoma. Histopathology of the breast specimen revealed a metaplastic carcinoma with pleomorphic and spindle cell features. The splenic biopsy showed non-tuberculous granulomatous inflammation. This case highlights a diagnostic challenge involving both histological similarities and imaging pitfalls. It emphasizes the importance of tissue diagnosis in FDG-avid lesions to prevent over-staging.