Heterogeneity of bone metastases as an important prognostic factor in patients affected by oestrogen receptor-positive breast cancer. The role of combined [18F]Fluoroestradiol PET/CT and [18F]Fluorodeoxyglucose PET/CT

Intrapatient 16α-[18F]Fluoro-17β-Estradiol PET Heterogeneity as a Prognostic Factor for Endocrine Therapy Response and Survival in Patients with Estrogen Receptor-Positive Metastatic Breast Cancer

Intrapatient heterogeneity of estrogen receptor (ER) expression on 16α-[18F]fluoro-17β-estradiol ([18F]FES) PET is related to outcome in patients with ER-positive metastatic breast cancer (MBC), but a validated and practical method to support clinical decision-making is lacking. Therefore, the [18F]FES PET heterogeneity score (i.e., percentage of [18F]FES-positive metastases) was validated as a prognostic factor for endocrine therapy response and survival in a large cohort of patients with newly diagnosed MBC. Furthermore, we explored 2 less laborious methods to predict the [18F]FES PET heterogeneity score. Methods: Patients with ER-positive MBC included in the IMPACT-MBC study, who received baseline [18F]FES and [18F]FDG PET and first-line endocrine therapy, were included in this subanalysis. ER homogeneous (100% [18F]FES-positive lesions) and ER heterogeneous (both [18F]FES-positive and [18F]FES-negative lesions) MBC was distinguished by manual segmentation of all lesions on [18F]FES PET and related to progression-free survival (PFS) and overall survival (OS). In addition, the positive predictive value of the visual assessment and the 5-largest-lesions assessment to predict homogeneous MBC in all lesions on [18F]FES PET was determined. Results: From the 102 MBC patients eligible for the present retrospective subanalysis, 46 had ER homogeneous MBC and 56 had ER heterogeneous MBC. Differences were found between ER homogeneous and ER heterogeneous MBC for median PFS (19.8 vs. 15.0 mo; hazard ratio, 0.63; 95% CI, 0.41-0.96; P = 0.03) and median OS (62.5 vs. 34.7 mo; hazard ratio, 0.65; 95% CI, 0.38-1.08; P = 0.09). Twenty-one (38%) of 61 patients with ER homogeneous MBC by visual analysis and 37 (45%) of 83 patients with ER homogeneous MBC by the 5-largest-lesions method had ER heterogeneous MBC by manual segmentation of all lesions on [18F]FES PET (positive predictive value, 0.66 and 0.55, respectively). Conclusion: Patients with ER-positive homogeneous MBC showed a trend toward superior PFS and OS compared with patients with ER heterogeneous MBC. This analysis confirmed and validated the prognostic value of the [18F]FES PET heterogeneity score for endocrine therapy response and survival in a large cohort of MBC patients. The less laborious visual and 5-largest-lesions methods were inferior compared with assessment based on the [18F]FES PET heterogeneity score in all lesions.

18F-Labeled Fluoroestradiol PET/CT: Current Status, Gaps in Knowledge, and Controversies-AJR Expert Panel Narrative Review

PET/CT using 16α-[18F]-fluoro-17β-estradiol (FES) noninvasively images tissues expressing estrogen receptors (ERs). FES has undergone extensive clinicopathologic validation for ER-positive breast cancer and in 2020 received FDA approval for clinical use as an adjunct to biopsy in patients with recurrent or metastatic ER-positive breast cancer. Clinical use of FES PET/CT is increasing but is not widespread in the United States. This AJR Expert Panel Narrative Review explores the present status and future directions of FES PET/CT, including image interpretation, existing and emerging uses, knowledge gaps, and current controversies. Specific controversies discussed include whether both FES PET/CT and FDG PET/CT are warranted in certain scenarios, whether further workup is required after negative FES PET/CT results, whether FES PET/CT findings should inform endocrine therapy selection, and whether immunohistochemistry should remain the stand-alone reference standard for determining ER status for all breast cancers. Consensus opinions from the panel include agreement with the appropriate clinical uses of FES PET/CT published by a multidisciplinary expert work group in 2023, anticipated expanded clinical use of FES PET/CT for staging ER-positive invasive lobular carcinomas and low-grade invasive ductal carcinomas pending ongoing clinical trial results, and the need for further research regarding the use of FES PET/CT for nonbreast malignancies expressing ER.

Bone Metastases

ABSTRACT

Bone metastases occur frequently in common malignancies such as breast and prostate cancer. They are responsible for considerable morbidity and skeletal-related events. Fortunately, there are now several systemic, focal, and targeted therapies that can improve quality and length of life, including radionuclide therapies. It is therefore important that bone metastases can be detected as early as possible and that treatment can be accurately and sensitively monitored. Several bone-specific and tumor-specific single-photon emission computed tomography and positron emission tomography molecular imaging agents are available, for detection and monitoring response to systemic therapeutics, as well as theranostic agents to confirm target expression and predict response to radionuclide therapies.

Can 18F-FES PET Improve the Evaluation of 18F-FDG PET in Patients With Metastatic Invasive Lobular Carcinoma?

PURPOSE

Invasive lobular carcinoma (ILC) exhibits a low affinity for 18F-FDG. The estrogen receptor (ER) is commonly expressed in ILCs, suggesting a potential benefit of targeting with the ER probe 18F-FES in this patient population. The objective of this study was to evaluate the diagnostic performance of 18F-FES imaging in patients with metastatic ILC and compare it with that of 18F-FDG.

METHODS

We conducted a retrospective analysis of 20 ILC patients who underwent concurrent 18F-FES and 18F-FDG PET/CT examinations in our center. 18F-FES and 18F-FDG imaging were analyzed to determine the total count of tracer-avid lesions in nonbone sites and their corresponding organ systems, assess the extent of anatomical regions involved in bone metastases, and measure the SUVmax values for both tracers.

RESULTS

Among 20 ILC patients, 65 nonbone lesions were found to be distributed in 13 patients, and 16 patients were diagnosed with bone metastasis, which was distributed in 54 skeletal anatomical regions. The detection rate of 18F-FDG in nonbone lesions was higher than that of 18F-FES (57 vs 37, P < 0.001). 18F-FES demonstrated a superior ability to detect nonbone lesions in 4 patients, whereas 18F-FDG was superior in 5 patients (P > 0.05). Among 9/16 patients with bone metastasis, 18F-FES demonstrated a significant advantage in the detection of bone lesions compared with 18F-FDG (P = 0.05). Furthermore, patients with only 18F-FES-positive lesions (12/12) were administered endocrine regimens, whereas patients lacking 18F-FES uptake (2/3) predominantly received chemotherapy.

CONCLUSIONS

18F-FES is more effective than 18F-FDG in detecting bone metastasis in ILC, but it does not demonstrate a significant advantage in nonbone lesions. Additionally, the results of examination with 18F-FES have the potential to guide patient treatment plans.

18F-FES and 18F-FDG PET/CT imaging as a predictive biomarkers for metastatic breast cancer patients undergoing cyclin-dependent 4/6 kinase inhibitors with endocrine treatment

OBJECTIVE

The aim of this study was to investigate the potential value of dual tracers 18F-FDG and 18F-FES PET/CT in predicting response to Cyclin-Dependent 4/6 Kinase (CDK4/6) inhibitors combined with endocrine therapy for metastatic estrogen receptor (ER)-positive breast cancer patients.

METHODS

This retrospective study enrolled 38 ER-positive metastatic breast cancer patients from our center who underwent both 18F-FDG and 18F-FES PET/CT scans within 1 month before CDK4/6 inhibitors combined with endocrine therapy. The extracted parameters comprised the maximum standardized uptake value (SUVmax) for both FDG and FES PET, as well as the ratio between FES and FDG SUVmax. Each parameter was dichotomized based on its median threshold. The primary endpoint was progression-free survival (PFS), which was estimated using the Kaplan-Meier method and compared by the log-rank test.

RESULTS

After a median follow-up of 15.6 months, progressive disease was observed in 23 out of 38 patients, and the median PFS for the whole cohort was 21.0 months [95% confidence interval (CI) 12.7-29.3]. FES and FDG PET identified 6 patients (15.8%) with FES-negative lesions, suggesting ER heterogeneity in metastatic lesions. The median PFS of these patients was only 5.3 months (95% CI 1.7-8.9), which was substantially shorter than that of patients with 100% FES-positive lesions (median PFS 22.9 months, 95% CI 17.1-28.7, P < 0.001). Patients with 100% FES-positive lesions who had high FES/FDG showed significantly shorter PFS compared to those with low FES/FDG (14.9 vs. 30.5 months, P = 0.003).

CONCLUSIONS

This study shows that FDG and FES PET imaging may serve as valuable tools for patient selection in the context of CDK4/6 inhibitor therapy combined with endocrine treatment, and have the potential to function as prognostic biomarkers.

The Application of 18F-FES PET in Clinical Cancer Care: A Systematic Review

INTRODUCTION

[18F]fluoroestradiol (FES) can be used for the noninvasive visualization and quantification of tumor estrogen receptor (ER) expression and activity and was FDA-approved as a diagnostic agent in May 2022 for detecting ER-positive lesions in patients with recurrent or metastatic breast cancer. PET imaging was also used to detect ER-positive lesions and malignancy among patients with uterine, ovarian, and other ER-positive solid tumors. We conducted a systemic review of the studies on FES PET imaging used among patients with cancer not limited to breast cancer to better understand the application of FES PET imaging.

METHODS

PubMed/MEDLINE and Cochrane Library databases were used to perform a comprehensive and systematic search and were updated until August 15, 2022. Two authors independently reviewed the titles and abstracts of the retrieved articles by using the search algorithm and selected the articles based on the inclusion and exclusion criteria. All statistical analyses were conducted using R statistical software.

RESULTS

Forty-three studies with 2352 patients were included in the qualitative synthesis, and 23 studies with 1388 patients were included in the quantitative analysis, which estimated the FES-positive detection rate. Thirty-two studies (77%) included breast cancer patients in 43 included studies. The FES SUVmean was higher in patients with endometrial cancer (3.4-5.3) than in those with breast cancer (2.05) and uterine sarcoma (1.1-2.6). The pooled detection rates of FES PET imaging were 0.80 for breast and 0.84 for ovarian cancer patients, both similar to that of 18F-FDG. The FES uptake threshold of 1.1 to 1.82 could detect 11.1% to 45% ER heterogeneity, but the threshold of FES uptake did not have consistent predictive ability for prognosis among patients with breast cancer, unlike uterine cancer. However, FES uptake can effectively predict and monitor treatment response, especially endocrine therapy such as estradiol, ER-blocking agents (fulvestrant and tamifoxen), and aromatase inhibitors (such as letrozole and Z-endoxifen).

CONCLUSIONS

[18F]fluoroestradiol PET is not only a convenient and accurate diagnostic imaging tool for detecting ER-expressing lesions in patients with breast and ovarian cancer but also among patients with uterine cancer. [18F]fluoroestradiol PET is a noninvasive predictive and monitoring tool for treatment response and prognosis.

Molecular imaging as biomarker for treatment response and outcome in breast cancer

Molecular imaging, such as positron emission tomography (PET), is increasingly used as biomarker to predict and assess treatment response in breast cancer. The number of biomarkers is expanding with specific tracers for tumour characteristics throughout the body and this information can be used to aid the decision-making process. These measurements include metabolic activity using [18F]fluorodeoxyglucose PET ([18F]FDG-PET), oestrogen receptor (ER) expression using 16α-[18F]Fluoro-17β-oestradiol ([18F]FES)-PET and human epidermal growth factor receptor 2 (HER2) expression using PET with radiolabelled trastuzumab (HER2-PET). In early breast cancer, baseline [18F]FDG-PET is frequently used for staging, but limited subtype-specific data reduce its usefulness as biomarker for treatment response or outcome. Early metabolic change on serial [18F]FDG-PET is increasingly used in the neo-adjuvant setting as dynamic biomarker to predict pathological complete response to systemic therapy, potentially allowing de-intensification or step-up intensification of treatment. In the metastatic setting, baseline [18F]FDG-PET and [18F]FES-PET can be used as biomarker to predict treatment response, in triple-negative and ER-positive breast cancer, respectively. Metabolic progression on repeated [18F]FDG-PET appears to precede progressive disease on standard evaluation imaging; however, subtype-specific studies are limited and more prospective data are needed before implementation in clinical practice. Even though (repeated) [18F]FDG-PET, [18F]FES-PET and HER2-PEt all show promising results as biomarkers to predict therapy response and outcome, for eventual integration into clinical practice, future studies will have to clarify at what timepoint this integration has to optimally take place.

Summary: Appropriate Use Criteria for Estrogen Receptor-Targeted PET Imaging with 16α-18F-Fluoro-17β-Fluoroestradiol

PET imaging with 16α-¹⁸F-fluoro-17β-fluoroestradiol (¹⁸F-FES), a radiolabeled form of estradiol, allows whole-body, noninvasive evaluation of estrogen receptor (ER). ¹⁸F-FES is approved by the U.S. Food and Drug Administration as a diagnostic agent "for the detection of ER-positive lesions as an adjunct to biopsy in patients with recurrent or metastatic breast cancer." The Society of Nuclear Medicine and Molecular Imaging (SNMMI) convened an expert work group to comprehensively review the published literature for ¹⁸F-FES PET in patients with ER-positive breast cancer and to establish appropriate use criteria (AUC). The findings and discussions of the SNMMI ¹⁸F-FES work group, including example clinical scenarios, were published in full in 2022 and are available at https://www.snmmi.org/auc Of the clinical scenarios evaluated, the work group concluded that the most appropriate uses of ¹⁸F-FES PET are to assess ER functionality when endocrine therapy is considered either at initial diagnosis of metastatic breast cancer or after progression of disease on endocrine therapy, the ER status of lesions that are difficult or dangerous to biopsy, and the ER status of lesions when other tests are inconclusive. These AUC are intended to enable appropriate clinical use of ¹⁸F-FES PET, more efficient approval of FES use by payers, and promotion of investigation into areas requiring further research. This summary includes the rationale, methodology, and main findings of the work group and refers the reader to the complete AUC document.

Advances in PET/CT Imaging for Breast Cancer Patients and Beyond

Breast cancer is the most common cancer in women around the world and the fifth leading cause of cancer-related death [...].

Imaging of Bone Metastases in Breast Cancer

Bone metastases are a common site of spread in advanced breast cancer and responsible for morbidity and high health care costs. Imaging contributes to staging and response assessment of the skeleton and has been instrumental in guiding patient management for several decades. Historically this has been with radiographs, computed tomography and bone scans. More recently, molecular and hybrid imaging methods have undergone significant development, including the addition of single photon emission computed tomography/computed tomography to the bone scan, positron emission tomography, with bone-specific and tumor-specific tracers, and magnetic resonance imaging with complementary functional diffusion-weighted imaging. These have allowed different aspects of the abnormal biology associated with bone metastases to be explored. There is ability to interrogate the bone microenvironment with bone-specific tracers and cancer cell characteristics with tumor-specific methods that complement morphological appearances on computed tomography or magnetic resonance imaging. Alongside the advent of novel, more effective and nuanced therapies for bone metastases in breast cancer, there is accumulating evidence that the developments in imaging allow more sensitive and specific detection of bone metastases as well as more accurate and earlier assessment of treatment response leading to improvements in patient management.

Chemotherapy Shows a Better Efficacy Than Endocrine Therapy in Metastatic Breast Cancer Patients with a Heterogeneous Estrogen Receptor Expression Assessed by 18F-FES PET

Background: The heterogeneity of estrogen receptor (ER) expression has long been a challenge for the diagnosis and treatment strategy of metastatic breast cancer (MBC). A novel convenient method of ER detection using 18F-fluoroestradiol positron emission tomography/computed tomography (18F-FES PET/CT) offers a chance to screen and analyze MBC patients with ER uncertainty. Methods: MBC patients who received 18F-FES PET/CT were screened and patients with both FES positive (FES+) and negative (FES-) lesions were enrolled in this study. Progression-free survival (PFS) was estimated using the Kaplan−Meier method and was compared using the log-rank test. Results: A total of 635 patients were screened and 75 of 635 (11.8%) patients showed ER uncertainty; 51 patients received further treatment and were enrolled in this study. Among them, 20 (39.2%) patients received chemotherapy (CT), 21 (41.2%) patients received endocrine-based therapy (ET), and 10 (19.6%) patients received combined therapy (CT + ET). CT showed a better progression-free survival (PFS) compared with ET (mPFS 7.1 vs. 4.6 months, HR 0.44, 95% CI 0.20−0.93, p = 0.03). CT + ET did not improve PFS compared with either CT or ET alone (mPFS 4.4 months, p > 0.2). All three treatment options were well tolerated. Conclusions: 18F-FES PET/CT could identify patients with ER heterogeneity. Patients with bone metastasis are more likely to have ER heterogeneity. Patients with ER heterogeneity showed better sensitivity to CT rather than ET. Combined therapy of CT + ET did not improve the treatment outcome.

Diagnostic and Prognostic Role of 18F-Fluoroestradiol PET in Metastatic Breast Cancer: The Second Youth of an Older Theranostic Concept

Since the discovery of the role of female hormones in breast cancer (BC) pathophysiology, in vivo detection of oestrogen receptor (ER) distribution has been one of the major goals of nuclear medicine and molecular imaging [...]

Head-to-Head Comparison between 18F-FES PET/CT and 18F-FDG PET/CT in Oestrogen Receptor-Positive Breast Cancer: A Systematic Review and Meta-Analysis

¹⁸F-FDG PET/CT is a powerful diagnostic tool in breast cancer (BC). However, it might have a reduced sensitivity in differentiated, oestrogen receptor-positive (ER+) BC. In this setting, specific molecular imaging with fluorine-oestradiol (¹⁸F-FES) PET/CT could help in overcoming these limitations; however, the literature on the diagnostic accuracy of this method is limited. We therefore planned this systematic review and meta-analysis to compare ¹⁸F-FDG and ¹⁸F-FES PET/CT in ER+ BC patients. We performed a literature search to identify all studies performing a head-to-head comparison between the two methods; we excluded review articles, preclinical studies, case reports and small case series. Finally, seven studies were identified (overall: 171 patients; range: 7–49 patients). A patients-based analysis (PBA) showed that ¹⁸F-FDG and ¹⁸F-FES PET/CT had a similar high pooled sensitivity (97% and 94%, respectively) at the lesion-based analysis (LBA), ¹⁸F-FES performed slightly better than ¹⁸F-FDG (pooled sensitivity: 95% vs. 85%, respectively). Moreover, when we considered only the studies dealing with the restaging setting (n = 3), this difference in sensitivity was even more marked (98% vs. 81%, respectively). In conclusion, both tracers feature an excellent sensitivity in ER+ BC; however, ¹⁸F-FES PET/CT could be preferred in the restaging setting.