Image Quality and Interpretation of [18F]-FES-PET: Is There any Effect of Food Intake?

Molecular Imaging of Steroid Receptors in Breast Cancer

ABSTRACT

Steroid receptors regulate gene expression for many important physiologic functions and pathologic processes. Receptors for estrogen, progesterone, and androgen have been extensively studied in breast cancer, and their expression provides prognostic information as well as targets for therapy. Noninvasive imaging utilizing positron emission tomography and radiolabeled ligands targeting these receptors can provide valuable insight into predicting treatment efficacy, staging whole-body disease burden, and identifying heterogeneity in receptor expression across different metastatic sites. This review provides an overview of steroid receptor imaging with a focus on breast cancer and radioligands for estrogen, progesterone, and androgen receptors.

Diffuse bilateral 18F-Fluoroestradiol pulmonary uptake in patients with metastatic estrogen receptor positive breast cancer: A case report

INTRODUCTION

Breast cancer is the most commonly diagnosed cancer in women and hormonal therapy is an established treatment for estrogen receptor (ER) positive breast cancers. 18F-Fluoroestradiol (FES) is an emerging radiotracer used to determine hormone status in patients with ER positive breast cancer as FES specifically binds to the alpha subtype of estrogen receptors. As with all radiotracers, FES demonstrates background uptake within various tissues and organs besides the targeted breast cancer and metastatic disease. To date, FES has mostly been shown to demonstrate uptake within the lungs from metastatic disease or in a more focal region after radiation therapy.

CASE AND OUTCOMES

We present two patients with stage IV ER positive breast cancer who underwent FES positron emission tomography and computed tomography (PET/CT) scans to evaluate for metastatic disease; both of which demonstrated diffuse bilateral mild-moderate pulmonary uptake. The first patient had a severe lung injury which was improving but still present at the time of her FES PET/CT. The second patient had a remote history of prior right breast radiation therapy for a prior breast cancer as well as emphysema and mild interstitial disease.

DISCUSSION

To date, FES uptake within the lungs has been shown to be secondary to fibrotic changes secondary to prior radiation therapy and the uptake is localized to a focal region within the lung corresponding to the localized region around the tumor needing radiation therapy. We present two FES PET/CT scans that demonstrate diffuse bilateral mild-moderate uptake. We believe the first patient's bilateral FES uptake was secondary to inflammatory changes from her acute lung injury. Our second patient has a remote history of right breast radiation therapy that would not account for her diffuse lung uptake but does have emphysema and mild interstitial disease which can account for the FES uptake seen in her FES PET/CT.

CONCLUSION

18F-Fluoroestradiol is an emerging radiotracer that binds to estrogen receptors and is being used to determine hormone receptor status in women with ER positive breast cancers, which is the most commonly diagnosed cancer in women. Therefore, it's important to understand where it might demonstrate uptake and why. We highlighted two unique cases of mild-moderate pulmonary uptake of FES to provide further information about FES. Overall, we conclude that diffuse bilateral mild-moderate FES uptake within the lungs is likely secondary to inflammation, interstitial disease, or a combination thereof.

Non-conventional and Investigational PET Radiotracers for Breast Cancer: A Systematic Review

Breast cancer is one of the most common malignancies in women, with high morbidity and mortality rates. In breast cancer, the use of novel radiopharmaceuticals in nuclear medicine can improve the accuracy of diagnosis and staging, refine surveillance strategies and accuracy in choosing personalized treatment approaches, including radioligand therapy. Nuclear medicine thus shows great promise for improving the quality of life of breast cancer patients by allowing non-invasive assessment of the diverse and complex biological processes underlying the development of breast cancer and its evolution under therapy. This review aims to describe molecular probes currently in clinical use as well as those under investigation holding great promise for personalized medicine and precision oncology in breast cancer.

Analyzing the Estrogen Receptor Status of Liver Metastases with [18F]-FES-PET in Patients with Breast Cancer

Background: Positron emission tomography (PET) with 16α-[¹⁸F]-fluoro-17β-estradiol ([¹⁸F]-FES) can visualize estrogen receptor (ER) expression, but it is challenging to determine the ER status of liver metastases, due to high physiological [¹⁸F]-FES uptake. We evaluated whether [¹⁸F]-FES-PET can be used to determine the ER status of liver metastases, using corresponding liver biopsies as the gold standard. Methods: Patients with metastatic breast cancer (n = 23) were included if they had undergone a [¹⁸F]-FES-PET, liver metastasis biopsy, CT-scan, and [¹⁸F]-FDG-PET. [¹⁸F]-FES-PET scans were assessed by visual and quantitative analysis, tracer uptake was correlated with ER expression measured by immunohistochemical staining and the effects of region-of-interest size and background correction were determined. Results: Visual analysis allowed ER assessment of liver metastases with 100% specificity and 18% sensitivity. Quantitative analysis improved the sensitivity. Reduction of the region-of-interest size did not further improve the results, but background correction improved ER assessment, resulting in 83% specificity and 77% sensitivity. Using separate thresholds for ER+ and ER− metastases, positive and negative predictive values of 100% and 75%, respectively, could be obtained, although 30% of metastases remained inconclusive. Conclusion: In the majority of liver metastases, ER status can be determined with [¹⁸F]-FES-PET if background correction and separate thresholds are applied.