Abstract
1178
Objectives: To evaluate the value of 18F-FES PET to differentiate between metastases originating from different tumor types. Content Overview: More and more patients acquire dual primary tumors, even multiple primary tumors, because of varied reasons, such as environmental modifications, genetic predisposition, therapy, increased surveillance, or prolonged survival. Identifying the origin of metastasis in patients with different primary tumors is a clinical dilemma. Although 18F-FDG PET / CT as whole-body scans might identify metastatic lesions, it lacks specificity and cannot distinguish the source of metastases in patients with multiple primary tumors. Several studies have validated 16a-18F-fluoro-17β-estradiol (18F-FES) as a specificity examination to quantify and visualize molecular information about ER expression in breast cancer. More than 70% of patients with metastatic breast cancer (MBC) present with hormone receptor (HR)-positive disease, which makes endocrine therapy an important therapeutic option. Although the value of 18F-FES and 18F-FDG PET has been extensively studied in metastatic breast cancer, the study of 18F‑FES application in cases of multiple primary tumors is extremely limited. The aims of this educational exhibit were to evaluate the clinical impact of 18F‑FES in distinguishing the metastases that came from breast cancer or the second primary tumor. We will present one case, an ER-positive breast cancer patient had thyroid cancer with definite metastatic lesions were detected by 18F-FDG PET imaging. It was uncertain whether these originated from the ER-positive breast tumor or from thyroid cancer. 18F-FES showed uptake in all metastatic lesions, therefore, this patient received endocrine therapy for metastatic disease. For this patient, 18F-FES can identify the origin of metastases and assist physicians in making treatment decisions.