From One Cancer to Two: [¹⁸F]FES PET/CT Redirected Diagnosis and Therapy in a Metastatic Breast Cancer Patient.

A 59-year-old woman with an ulcerated right breast lesion was diagnosed with ER-positive invasive ductal carcinoma. Staging [¹⁸F]FDG PET/CT revealed intense uptake in the breast, axillary nodes, a large hypermetabolic pulmonary mass, mediastinal lymphadenopathies, and bone lesions. Because of this metabolic pattern, [¹⁸F]FES PET/CT was performed, demonstrating [¹⁸F]FES-avid bone metastases but no uptake in the lung mass. Biopsy confirmed a BRAF V600E-mutated lung adenocarcinoma. [¹⁸F]FES PET/CT proved crucial in differentiating synchronous primary malignancies from metastatic spread and guiding targeted therapy with dabrafenib-trametinib.