68Ga–Prostate-Specific Membrane Antigen PET/CT and 18F-FDG PET/CT of Primary Signet Ring Cell Breast Adenocarcinoma

Primary signet ring cell adenocarcinoma of the breast is a rare neoplasm. Similar to other mucinous neoplasms, it has low FDG avidity and poor prognosis compared with the traditional ductal/lobular carcinomas. We present a case of a 40-year-old woman with signet ring cell adenocarcinoma and skeletal fluorosis showing higher uptake of Ga-prostate-specific membrane antigen in the primary lesion and the metastatic sites compared with F-FDG on PET/CT imaging. Additionally, diffuse increased prostate-specific membrane antigen uptake was noticed in the entire skeleton, likely due to skeletal fluorosis.