Evaluation of estrogen expression of breast cancer using ¹⁸F-FES PET CT-A novel technique

Estrogen receptor (ER) expression in breast cancer is routinely studied on immunohistochemistry (IHC) of tissue obtained from core biopsy or surgical specimen. Sampling error and heterogeneity of tumor may incorrectly label a breast tumor as ER negative, thus denying patient hormonal treatment. Molecular functional ER imaging can assess the in-vivo ER expression of primary tumor and metastases at sites inaccessible for biopsy and also track changes in expression over time. The aim was to study ER expression using 16α-¹⁸F-fluoro-17β-estradiol or ¹⁸F-fluoroestradiol (¹⁸F FES) positron emission tomography (PET) computed tomography (CT). Twenty-four biopsy-proven breast cancer patients consenting to participate in the study underwent FES PET CT. Standard uptake value (SUV_mean) of maximum of 7 lesions/patient was analyzed, and tumor-to-background ratio was calculated for each lesion. Visual interpretation score was calculated for lesion on FES PET and correlated with the Allred score on IHC of tumor tissue samples for ER expression. The diagnostic indices of FES PET CT were assessed taking IHC as "gold standard." On FES PET CT, the mean SUV for ER+ tumors was 4.75, whereas the mean SUV for ER - tumors was 1.41. Using receiver operating characteristic curve, tumors with an SUV of ≥ 1.8 on FES PET could be considered as ER+. The overall accuracy of FES PET CT to detect ER expression was 91.66%, with two false negatives noted in this study. ¹⁸F-FES PET CT appears promising in evaluating ER expression in breast cancer. It is noninvasive and has potential to assess the in-vivo ER expression of the entire primary tumor and metastasis not amenable for biopsy.