Synchronous bilateral breast cancer is a rare condition, accounting for approximately 2–5% of all breast cancer diagnoses, and poses significant challenges for staging and treatment planning, particularly in luminal tumors, in which PET-FDG has limited sensitivity for detecting metastatic disease (1,2). PET-FES, which evaluates estrogen receptor expression, has demonstrated greater accuracy in identifying metastatic lesions, thereby enabling more precise therapeutic decision-making (2–5).

We report the case of a 75-year-old woman with bilateral luminal breast cancer diagnosed by biopsy and immunohistochemistry showing positive hormone receptor expression. Initial PET-FDG imaging revealed no evidence of metastatic disease, suggesting stage III cancer and leading to a conventional treatment plan based on chemotherapy. However, subsequent PET-FES identified multiple bone and liver metastases, resulting in disease upstaging to stage IV. Based on these findings, conventional chemotherapy was discontinued and replaced with targeted therapy consisting of a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor combined with endocrine therapy, reducing systemic toxicity and significantly improving the patient's quality of life.

This case highlights the contribution of PET-FES to precision oncology by enabling individualized treatment strategies, avoiding unnecessary therapies, and optimizing clinical outcomes (2,4,5). Although based on a single case, it reinforces the potential of this imaging modality to influence clinical decision-making, improve resource allocation, and reduce patient exposure to aggressive treatments without clear benefit. This report illustrates how advanced functional imaging can redefine cancer staging and therapeutic management, representing a significant advance in personalized medicine while providing evidence to support future studies evaluating the incorporation of PET-FES into national clinical protocols for bilateral luminal breast cancer.

To be updated soon