Purpose: It is known that the estrogen receptor (ER) status of a tumor is an important prognostic and predictive indicator in breast cancer. Women with ER-positive breast tumors have a better prognosis than women with ER-negative tumors in terms of responsiveness to anti-estrogen treatment. 16α-[ 18 F]-Fluoro-17β-estradiol ( 18 F-FES) has proven to be a promising tracer for in vivo imaging studies of the ER status of primary and metastatic breast cancer. Consequently, at our Institution

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... emission tomography/computed tomography (PET/CT) using estradiol, labelled with fluorine-18, is an important diagnostic tool to be used in hormone-dependent breast cancer. Materials and Methods: To date, we have applied this 18 F-FES-PET/CT method in 18 breast cancer patient examinations. We have evaluated by means of 18 F-FES, the location of the disease, preoperatively in one patient and in the remaining 17 patients we used 18 F-FES-PET/CT for the follow-up/planning of hormonal therapy and/or radiation therapy and chemotherapy. Results: The patient group has so far revealed 148 60 metastatic lesions in 18 F-FES-PET/CT imaging. Lesions were located: 1 lesion (0.67%) in primary tumor in the unoperated patient, 15 lesions (10.1%) in lymph nodes, 2 lesions (1.35%) in lungs and 130 lesions (87.8%) in bones. Mean SUVmax in the primary tumor was 1.5; in lymph nodes 6.24±2.5 (2.4-8.8) and in bones 8. 6±4.7 (1.5-22.4). In lungs, there were only 2 lesions -SUVmax 7.5 and 3.5, respectively. In 5 out of 18 patients (27.7%) the therapy was changed after 18 F-FES-PET/CT study. There was a good correlation between SUVmax of lesions on 18 F-FES-PET/CT and tumor marker CEA as well as number of lesions and the CEA level. Conclusion: On the basis of this preliminary work, we know that tumor imaging with 18 F-FES PET/CT is useful in the determination of ER status and prognosis of hormonal therapy for breast cancer patients. We suggest potential scenarios where this functional metabolic imaging might be considered in clinical use for guiding ER-positive breast cancer treatment in problematic individual cases.