Visual and quantitative evaluation of [18F]FES and [18F]FDHT PET in patients with metastatic breast cancer: an interobserver variability study

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.

[18F]-FDHT PET for the Imaging of Androgen Receptor in Prostate and Breast Cancer: A Systematic Review

The aim of this systematic review is to provide a comprehensive overview of the role of fluoro-5α-dihydrotestosterone ([18F]-FDHT) for the in vivo imaging of androgen receptors (AR) through positron emission tomography (PET) in metastatic breast (mBC) and metastatic castration-resistant prostate cancer (mCRPC). Relevant studies published from 2013 up to May 2023 were selected by searching Scopus, PubMed and Web of Science. The selected imaging studies were analyzed using a modified version of the critical Appraisal Skills Programme (CASP). Eleven studies encompassing 321 patients were selected. Seven of the eleven selected papers included 266 subjects (82.2%) affected by mCRPC, while four encompassed 55 (17.2%) patients affected by mBC. [18F]-FDHT PET showed a satisfying test/retest reproducibility, and when compared to a histochemical analysis, it provided encouraging results for in vivo AR quantification both in mCRPC and mBC. [18F]-FDHT PET had a prognostic relevance in mCRPC patients submitted to AR-targeted therapy, while a clear association between [18F]-FDHT uptake and the bicalutamide response was not observed in women affected by AR-positive mBC. Further studies are needed to better define the role of [18F]-FDHT PET, alone or in combination with other tracers (i.e., [18F]-FDG/[18F]-FES), for patients' selection and monitoring during AR-targeted therapy, especially in the case of mBC.

Diagnostic effectiveness of [18F]Fluoroestradiol PET/CT in oestrogen receptor-positive breast cancer: the key role of histopathology. Evidence from an international multicentre prospective study

INTRODUCTION

[18F]Fluoroestradiol ([18F]FES) PET/CT has been proposed as a tool for detecting the oestrogen receptor density in patients with metastatic breast cancer (BC) non-invasively across all disease localizations. However, its diagnostic potential in terms of the detection rate (DR) of metastases is unclear. In this study, we pitted this method against [18F]FDG PET/CT and tried to identify predictors of the diagnostic superiority of the [18F] FES-based method.

MATERIALS AND METHODS

From a multicentre database, we enrolled all patients with metastatic BC who had undergone both [18F]FES PET/CT and [18F]FDG PET/CT. Two readers assessed both images independently and used a patient-based (PBA) and lesion-based analysis (LBA) to calculate the DR. Pathology-related and clinical factors were tested as predictors of [18F]FES PET/CT superiority using a multivariate model.

RESULTS

92 patients, bearing a total of 2678 metastases, were enrolled. On PBA, the DR of [18F]FDG and [18F]FES PET/CT was 97% and 86%, respectively (p = 0.018). On LBA, the [18F]FES method proved more sensitive than [18F]FDG PET/CT in lymph nodes, bone, lung and soft tissue (p < 0.01). This greater sensitivity was associated with lobular histology, both on PBA (Odds Ratio (OR) 3.4, 95%CI 1.0-12.3) and on LBA (OR 4.4, 95%CI 1.2-16.1 for lymph node metastases and OR 3.29, 95%CI 1.1-10.2 for bone localizations).

CONCLUSIONS

The overall DR of [18F]FES PET/CT appears to be lower than that of [18F]FDG PET/CT on PBA. However, the [18F]FES method, if positive, can identify more lesions than [18F]FDG at most sites. The higher sensitivity of [18F]FES PET/CT was associated with lobular histology.

Androgen Receptor Imaging in the Management of Hormone-Dependent Cancers with Emphasis on Prostate Cancer

Prostate cancer is dependent on the action of steroid hormones on the receptors. Endocrine therapy inhibits hormone production or blocks the receptors, thus providing clinical benefit to many, but not all, oncological patients. It is difficult to predict which patient will benefit from endocrine therapy and which will not. Positron Emission Tomography (PET) imaging of androgen receptors (AR) may provide functional information on the likelihood of endocrine therapy response in individual patients. In this article, we review the utility of [¹⁸F]FDHT-PET imaging in prostate, breast, and other hormone-dependent cancers expressing AR. The methodologies, development, and new possibilities are discussed as well.

The Role of PET/CT in Breast Cancer

Female breast cancer has surpassed lung cancer as the most commonly diagnosed cancer worldwide, with an estimated 2.3 million new cases (11.7%), followed by lung cancer (11.4%) The current literature and the National Comprehensive Cancer Network (NCCN) guidelines state that ¹⁸F-FDG PET/CT is not routine for early diagnosis of breast cancer, and rather PET/CT scanning should be performed for patients with stage III disease or when conventional staging studies yield non-diagnostic or suspicious results because this modality has been shown to upstage patients compared to conventional imaging and thus has an impact on disease management and prognosis. Furthermore, with the growing interest in precision therapy in breast cancer, numerous novel radiopharmaceuticals have been developed that target tumor biology and have the potential to non-invasively guide the most appropriate targeted therapy. This review discusses the role of ¹⁸F-FDG PET and other PET tracers beyond FDG in breast cancer imaging.

To Identify Small Bowel Metastasis From Lobular Breast Cancer on 18 F-Fluoroestradiol PET/CT : Necessary to Adjust the Background Uptake Level

ABSTRACT

A 61-year-old woman was incidentally found to have small bowel metastasis from an undiagnosed lobular breast cancer in a workup for her acute presentation of small bowel obstruction. However, outside-hospital mammogram and breast ultrasound failed to reveal primary breast cancer. At 3.5 months postsurgery, the patient transferred her care to our hospital and received initial staging 18 F-fluoroestradiol (FES) PET/CT. The occult primary right breast cancer and previously biopsied right axilla lymph node were visualized on FES PET/CT. The intense small bowel uptake of FES was initially considered as physiological; however, after readjusting the background FES level on PET, an intense focus at small bowel anastomosis site became obvious.

Nuclear Receptor Imaging In Vivo-Clinical and Research Advances

Nuclear receptors are transcription factors that function in normal physiology and play important roles in diseases such as cancer, inflammation, and diabetes. Noninvasive imaging of nuclear receptors can be achieved using radiolabeled ligands and positron emission tomography (PET). This quantitative imaging approach can be viewed as an in vivo equivalent of the classic radioligand binding assay. A main clinical application of nuclear receptor imaging in oncology is to identify metastatic sites expressing nuclear receptors that are targets for approved drug therapies and are capable of binding ligands to improve treatment decision-making. Research applications of nuclear receptor imaging include novel synthetic ligand and drug development by quantifying target drug engagement with the receptor for optimal therapeutic drug dosing and for fundamental research into nuclear receptor function in cells and animal models. This mini-review provides an overview of PET imaging of nuclear receptors with a focus on radioligands for estrogen receptor, progesterone receptor, and androgen receptor and their use in breast and prostate cancer.

Clinical Evaluation of Nuclear Imaging Agents in Breast Cancer

Precision medicine is the customization of therapy for specific groups of patients using genetic or molecular profiling. Noninvasive imaging is one strategy for molecular profiling and is the focus of this review. The combination of imaging and therapy for precision medicine gave rise to the field of theranostics. In breast cancer, the detection and quantification of therapeutic targets can help assess their heterogeneity, especially in metastatic disease, and may help guide clinical decisions for targeted treatments. Positron emission tomography (PET) or single-photon emission tomography (SPECT) imaging has the potential to play an important role in the molecular profiling of therapeutic targets in vivo for the selection of patients who are likely to respond to corresponding targeted therapy. In this review, we discuss the state-of-the-art nuclear imaging agents in clinical research for breast cancer. We reviewed 17 clinical studies on PET or SPECT agents that target 10 different receptors in breast cancer. We also discuss the limitations of the study designs and of the imaging agents in these studies. Finally, we offer our perspective on which imaging agents have the highest potential to be used in clinical practice in the future.

Bone Metastases Are Measurable: The Role of Whole-Body MRI and Positron Emission Tomography

Metastatic tumor deposits in bone marrow elicit differential bone responses that vary with the type of malignancy. This results in either sclerotic, lytic, or mixed bone lesions, which can change in morphology due to treatment effects and/or secondary bone remodeling. Hence, morphological imaging is regarded unsuitable for response assessment of bone metastases and in the current Response Evaluation Criteria In Solid Tumors 1.1 (RECIST1.1) guideline bone metastases are deemed unmeasurable. Nevertheless, the advent of functional and molecular imaging modalities such as whole-body magnetic resonance imaging (WB-MRI) and positron emission tomography (PET) has improved the ability for follow-up of bone metastases, regardless of their morphology. Both these modalities not only have improved sensitivity for visual detection of bone lesions, but also allow for objective measurements of bone lesion characteristics. WB-MRI provides a global assessment of skeletal metastases and for a one-step "all-organ" approach of metastatic disease. Novel MRI techniques include diffusion-weighted imaging (DWI) targeting highly cellular lesions, dynamic contrast-enhanced MRI (DCE-MRI) for quantitative assessment of bone lesion vascularization, and multiparametric MRI (mpMRI) combining anatomical and functional sequences. Recommendations for a homogenization of MRI image acquisitions and generalizable response criteria have been developed. For PET, many metabolic and molecular radiotracers are available, some targeting tumor characteristics not confined to cancer type (e.g. 18F-FDG) while other targeted radiotracers target specific molecular characteristics, such as prostate specific membrane antigen (PSMA) ligands for prostate cancer. Supporting data on quantitative PET analysis regarding repeatability, reproducibility, and harmonization of PET/CT system performance is available. Bone metastases detected on PET and MRI can be quantitatively assessed using validated methodologies, both on a whole-body and individual lesion basis. Both have the advantage of covering not only bone lesions but visceral and nodal lesions as well. Hybrid imaging, combining PET with MRI, may provide complementary parameters on the morphologic, functional, metabolic and molecular level of bone metastases in one examination. For clinical implementation of measuring bone metastases in response assessment using WB-MRI and PET, current RECIST1.1 guidelines need to be adapted. This review summarizes available data and insights into imaging of bone metastases using MRI and PET.

[18F]FDG and [18F]FES positron emission tomography for disease monitoring and assessment of anti-hormonal treatment eligibility in granulosa cell tumors of the ovary

Purpose: Adult granulosa cell tumors (AGCTs) of the ovary represent a rare malignancy in which timing and choice of treatment is a clinical challenge. This study investigates the value of FDG-PET/CT and FES-PET/CT in monitoring recurrent AGCTs and assessing eligibility for anti-hormonal treatment.

Materials and Methods: We evaluated 22 PET/CTs from recurrent AGCT patients to determine tumor FDG (n = 16) and FES (n = 6) uptake by qualitative and quantitative analysis. We included all consecutive patients from two tertiary hospitals between 2003-2020. Expression of ERα and ERβ and mitoses per 2 mm² were determined by immunohistochemistry and compared to FES and FDG uptake, respectively.

Results: Qualitative assessment showed low-to-moderate FDG uptake in most patients (14/16), and intense uptake in 2/16. One patient with intense tumor FDG uptake had a high mitotic rate (18 per 2 mm²) Two out of six patients showed FES uptake on PET/CT at qualitative analysis. Lesion-based quantitative assessment showed a mean SUV_max of 2.4 (± 0.9) on FDG-PET/CT and mean SUV_max of 1.7 (± 0.5) on FES-PET/CT. Within patients, expression of ERα and ERβ varied and did not seem to correspond with FES uptake. In one FES positive patient, tumor locations with FES uptake remained stable or decreased in size during anti-hormonal treatment, while all FES negative locations progressed.

Conclusions: This study shows that in AGCTs, FDG uptake is limited and therefore FDG-PET/CT is not advised. FES-PET/CT may be useful to non-invasively capture the estrogen receptor expression of separate tumor lesions and thus assess the potential eligibility for hormone treatment in AGCT patients.

Positron Emission Tomography-Based Response to Target and Immunotherapies in Oncology

2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) is a promising tool to support the evaluation of response to either target therapies or immunotherapy with immune checkpoint inhibitors both in clinical trials and, in selected patients, at the single patient's level. The present review aims to discuss available evidence related to the use of [¹⁸F]FDG PET (Positron Emission Tomography) to evaluate the response to target therapies and immune checkpoint inhibitors. Criteria proposed for the standardization of the definition of the PET-based response and complementary value with respect to morphological imaging are commented on. The use of PET-based assessment of the response through metabolic pathways other than glucose metabolism is also relevant in the framework of personalized cancer treatment. A brief discussion of the preliminary evidence for the use of non-FDG PET tracers in the evaluation of the response to new therapies is also provided.