Molecular imaging to identify patients with metastatic breast cancer who benefit from endocrine treatment combined with cyclin-dependent kinase inhibition

Head-to-Head comparison of [18F]FES and [18F]FDG PET/CT in breast cancer patients: has a new era come?

PURPOSE

This review systematically compared, in a head-to-head manner, the diagnostic and prognostic performance of [18F]FDG and [18F]FES PET/CT in breast cancer (BC) patients.

METHODS

A systematic literature search was conducted in PubMed, Scopus, and Web of Science databases up to January 2025, without temporal limitations or restrictions on the number of patients in the included studies, to identify relevant articles comparing the diagnostic value of [18F]FDG and [18F]FES PET in BC patients. Selected imaging studies were analyzed using a modified version of the Critical Appraisal Skills Programme checklist dedicated to systematic reviews.

RESULTS

A total of 20 papers were evaluated. Based on the CASP analysis, the quality of the study was variable. Totally, 806 patients affected by BC underwent both [18F]FDG and [18F]FES PET. Different setting of disease were considered, such as staging/diagnostic and prognostic value. In the initial staging of disease, [18F]FES PET/CT seemed to be more accurate than [18F]FDG. In the prognostic field, [18F]FES expression was a positive factor for the better prognosis, in particular when the amount of [18F]FDG uptake was low. [18F]FES seemed to be promising as a molecular agent in patients affected by invasive lobular BC.

CONCLUSION

These findings underscore the potential of [18F]FES as a complementary imaging biomarker to [18F]FDG, advocating for further studies to standardize PET metrics and refine their combined clinical utility.

[18 F]-Fluoroestradiol PET (FES-PET) and [18 F] Flurodeoxyglucose PET (FDG-PET) Imaging May Aid in Managing Therapy in Patients with Metastatic Lobular Breast Cancer

AIM

This study examines the combination of FES-PET and FDG-PET as complementary imaging for detection of metastatic ILC.

METHODS

We retrospectively evaluated FES and FDG uptake in patients with metastatic ILC from an estrogen receptor (ER) positive primary tumor. We classified lesions into three categories (FES high/FDG low, FES high/FDG high, FES low/FDG low) using SUVmax cut-off values of 1.5 for FES and 5.0 for FDG. Qualitative evaluation included examination of the difference in the extent of disease between FES and FDG.

RESULTS

Of the 38 patients, 82% had FES uptake in all tumor sites identified by FDG, with 18% lacking FES uptake in at least one lesion. Mean (range) SUVmax for FES and FDG was 4.0 (0.67-10.6) and 4.6 (1.3-12.5), respectively. The majority of ILC patients (25/38), had lesions with FES high/FDG low uptake, consistent with the strongly ER + indolent nature of ILC. Patients with disease classified as FES high/FDG low had longer median overall survival (OS) (3.2 years) and progression-free survival (PFS) (1.5 years) than FES high/FDG high (OS = 2.1 years and PFS = 0.46 years). The median overall OS for all patients was 3.0 years (95% CI 2.5, 4.8) and PFS of 1.3 years (95% CI 0.6, 2.5). 8 patients (21%) had qualitatively more extensive disease by FES-PET.

CONCLUSIONS

Our findings suggest that both FES-PET and FDG-PET can identify metastatic ILC and be useful in detecting the pattern and extent of disease. The imaging combination provides additional information for prognosis and clinical decision making, balancing suitability for endocrine therapy and aggressiveness/indolence of disease.

The Role of [18F]FES PET/CT in Breast Cancer Management: An Umbrella Review

Background/Objectives: Breast cancer (BC) is the most commonly diagnosed cancer worldwide. Estrogen receptor (ER) status is a key determinant in the diagnosis and treatment of BC. Although immunohistochemistry (IHC) is the gold standard for ER assessment, it has limitations. This umbrella review aims to evaluate the role of 16α-18F-fluoro-17β-estradiol ([18F]FES) PET/CT as a non-invasive imaging tool for assessing ER expression and its implications in BC management. Methods: A comprehensive search was conducted in PubMed/MEDLINE and Cochrane Library for systematic reviews and meta-analyses published in the last decade. Studies eligible for inclusion evaluated the diagnostic accuracy and clinical utility of [18F]FES PET/CT in BC based on a predefined research question "What is the role of fluoroestradiol ([18F]FES) PET/CT in breast cancer?". Data extraction and quality assessment were performed independently by two reviewers using the AMSTAR-2 tool. Results: Eight systematic reviews met the inclusion criteria. [18F]FES PET/CT demonstrated high sensitivity (81-94%) and specificity (78-95%) in detecting ER-positive lesions. It provided a real-time, whole-body assessment of ER expression, outperforming IHC in detecting functional ER activity. Additionally, [18F]FES PET/CT showed promise in predicting treatment response and guiding therapy decisions, particularly in metastatic settings. Conclusions: This review highlights the clinical value of [18F]FES PET/CT in BC management, offering a non-invasive alternative for ER assessment with high diagnostic accuracy. Its integration into clinical practice may enhance personalized treatment strategies for BC patients.

Evaluating Automated Tools for Lesion Detection on 18F Fluoroestradiol PET/CT Images and Assessment of Concordance with Standard-of-Care Imaging in Metastatic Breast Cancer

Purpose To evaluate two automated tools for detecting lesions on fluorine 18 (18F) fluoroestradiol (FES) PET/CT images and assess concordance of 18F-FES PET/CT with standard diagnostic CT and/or 18F fluorodeoxyglucose (FDG) PET/CT in patients with breast cancer. Materials and Methods This retrospective analysis of a prospective study included participants with breast cancer who underwent 18F-FES PET/CT examinations (n = 52), 18F-FDG PET/CT examinations (n = 13 of 52), and diagnostic CT examinations (n = 37 of 52). A convolutional neural network was trained for lesion detection using manually contoured lesions. Concordance in lesions labeled by a nuclear medicine physician between 18F-FES and 18F-FDG PET/CT and between 18F-FES PET/CT and diagnostic CT was assessed using an automated software medical device. Lesion detection performance was evaluated using sensitivity and false positives per participant. Wilcoxon tests were used for statistical comparisons. Results The study included 52 participants. The lesion detection algorithm achieved a median sensitivity of 62% with 0 false positives per participant. Compared with sensitivity in overall lesion detection, the sensitivity was higher for detection of high-uptake lesions (maximum standardized uptake value > 1.5, P = .002) and similar for detection of large lesions (volume > 0.5 cm3, P = .15). The artificial intelligence (AI) lesion detection tool was combined with a standardized uptake value threshold to demonstrate a fully automated method of labeling patients as having FES-avid metastases. Additionally, automated concordance analysis showed that 17 of 25 participants (68%) had over half of the detected lesions across two modalities present on 18F-FES PET/CT images. Conclusion An AI model was trained to detect lesions on 18F-FES PET/CT images and an automated concordance tool measured heterogeneity between 18F-FES PET/CT and standard-of-care imaging. Keywords: Molecular Imaging-Cancer, Neural Networks, PET/CT, Breast, Computer Applications-General (Informatics), Segmentation, 18F-FES PET, Metastatic Breast Cancer, Lesion Detection, Artificial Intelligence, Lesion Matching Supplemental material is available for this article. Clinical Trials Identifier: NCT04883814 Published under a CC BY 4.0 license.

Predictive and prognostic value of 18F-FES PET/CT for patients with recurrent or metastatic breast cancer treated with endocrine therapy plus cyclin-dependent kinase 4/6 inhibitors

PURPOSE

Estrogen receptor (ER) expression and heterogeneity affect endocrine therapy efficacy. 18F-fluoroestradiol (18F-FES) PET/CT is an effective non-invasive method to analyze systemic ER expression. This study aimed to examine the predictive/prognostic value of 18F-FES PET/CT for patients treated with endocrine therapy plus cyclin-dependent kinase 4/6 (CDK4/6) inhibitors.

METHODS

Patients were identified from a prospective cohort for post-marketing surveillance of 18F-FES enrolled between April 2021 and April 2023 at Asan Medical Center. In this retrospective analysis, patients with ER-positive, HER2-negative recurrent/metastatic breast cancer who underwent CDK4/6 inhibitor-based endocrine therapy and pre-treatment 18F-FES PET/CT were included.

RESULTS

A total of 127 women were included. The endocrine therapy used was aromatase inhibitors in 96 patients (76%) and fulvestrant in 31 patients (24%). There were 25 (20%) and 102 (80%) patients in the "with FES-negative" (3 completely negative, 22 mixed) and "FES-positive" groups, respectively. 18F-FES status correlated with progression-free survival (PFS) following endocrine therapy with CDK4/6 inhibitors and overall survival (OS) ("with FES-negative" group: hazard ratio for PFS, 3.9, p < 0.001; for OS, 3.7, p = 0.008). Reduced benefit from endocrine treatment in the "with FES-negative" group was consistent across subgroups including menopausal status, endocrine sensitivity, and treatment regimen.

CONCLUSION

ER expression determined by 18F-FES PET/CT predicted the efficacy of CDK4/6 inhibitor-based endocrine therapy and was prognostic for survival in recurrent/metastatic ER-positive, HER2-negative breast cancer.

18F-Fluoroestradiol PET/CT for Predicting Benefit from Endocrine Therapy in Patients with Estrogen Receptor-Positive Breast Cancer: A Systematic Review and Metaanalysis

18F-fluoroestradiol (18F-FES) PET/CT has been investigated as a potential biomarker to predict response to endocrine therapies in patients with estrogen receptor (ER)-positive breast cancer. Although previous findings were promising, most had limited statistical significance because of small individual sample sizes. Therefore, we performed a systematic review and metaanalysis of the 18F-FES PET/CT literature to increase our power to evaluate the utility of 18F-FES PET/CT as a biomarker for prediction of clinical benefit from endocrine therapy in patients with ER-positive breast cancer. Methods: A comprehensive literature search was conducted across multiple databases, including PubMed, MEDLINE via OVID, Embase, Web of Science, Emcare, and the Cochrane Central Register of Controlled Trials through November 1, 2024, for studies that included patients with ER-positive breast cancer who received an 18F-FES PET/CT at baseline and received subsequent endocrine therapy. For each eligible study, data were extracted using a predesigned data extraction form. Random effects models were used to estimate the likelihood of clinical benefit from endocrine therapy after a positive 18F-FES PET scan, the likelihood of clinical benefit from endocrine therapy after a negative 18F-FES PET scan, and the risk ratio of clinical benefit from endocrine therapy comparing those who were 18F-FES-positive to those who were 18F-FES-negative. Results: From 1,105 database records retrieved, 12 studies were included in the metaanalysis (n = 308 participants with data on 18F-FES PET results and response to endocrine therapy). The likelihood of clinical benefit after a positive 18F-FES PET scan was 66% (95% CI, 51%-79%; I 2 = 76.6%; n = 227 participants) and the likelihood after a negative 18F-FES PET scan was 11% (95% CI, 3.5%-22%; I 2 = 0.0%; n = 81 participants). The risk ratio of response that compared those who were 18F-FES-positive with those who were 18F-FES-negative was 3.21 (95% CI, 1.96-5.25; I 2 = 0.0%; P < 0.0001). Conclusion: 18F-FES PET is a successful biomarker for predicting the likelihood of success of endocrine therapy in patients with ER-positive breast cancer. There is strong evidence that patients with 18F-FES-negative disease are unlikely to derive clinical benefit from endocrine therapies, despite the presence of ER-positive disease on pathology. This supports a role for 18F-FES PET in identifying patients for whom endocrine therapy may or may not be an appropriate treatment option.

[Molecular imaging and radioligand in breast cancer]

Molecular imaging plays a crucial role in the diagnosis, staging, and monitoring of breast cancer. The most commonly used tracer at present is 18F-FDG, a marker of cellular metabolism, making 18F-FDG PET/CT a major imaging modality in the management of breast neoplasms. However, this tracer has limitations, particularly for low-grade ductal or lobular neoplasms, which exhibit low avidity for 18F-FDG. The 68Ga-FAPI tracer, which targets activated fibroblasts and whose uptake is independent of tumor aggressiveness, is currently under investigation and could serve as an excellent alternative to 18F-FDG in certain cases. Additionally, new tracers targeting novel biological pathways of the tumor, including hormonal receptors or HER2, are being developed. These tracers enable whole-body assessment of specific biomarker expressions on cancer cells, offering a more precise understanding of the disease. This approach could help tailor treatments to the molecular characteristics of each tumor, enabling personalized strategies that improve therapeutic efficacy and patient quality of life. Finally, inspired by the model of 177Lu-PSMA used in prostate cancer, researchers are exploring the potential to couple these tracers with therapeutic agents to develop targeted radionuclide therapy for breast neoplasms.

[18F]F-FES PET for diagnosis, staging, and endocrine therapy prediction in ER-positive breast cancer: a systematic review and meta-analysis

BACKGROUND

This meta-analysis evaluates the diagnostic and staging accuracy of [18F]F-FES PET/CT, its ability to detect estrogen receptor (ER) positivity, and its effectiveness in predicting response to endocrine therapy in ER-positive (ER+) breast cancer. A systematic search of PubMed, Embase (OVID), and Web of Science databases was conducted for studies published between 2013 and June 2024. Studies involving ER + breast cancer patients who underwent [18F]F-FES PET/CT were included. We analyzed the diagnostic accuracy, ER detection capability, and predictive ability for endocrine therapy response.

RESULTS

Out of 189 studies initially identified, 21 met the inclusion criteria. For diagnosis and staging compared to [18F]F-FDG PET (10 studies), [18F]F-FES PET/CT demonstrated a sensitivity of 0.75 (95% CI: 0.62-0.85) and a false positive rate (FPR) of 0.27 (95% CI: 0.09-0.50). For ER detection (7 studies), sensitivity was 0.86 (95% CI: 0.71-0.94) with an FPR of 0.45 (95% CI: 0.19-0.73). For predicting response to endocrine therapy (12 studies), [18F]F-FES PET/CT showed a sensitivity of 0.79 (95% CI: 0.62-0.89) and an FPR of 0.58 (95% CI: 0.42-0.72).

CONCLUSIONS

[18F]F-FES PET/CT is valuable for diagnosing and staging ER + breast cancer, assessing ER status, and predicting response to endocrine therapy. Its implementation can improve treatment planning and patient outcomes in breast cancer management.

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.

A Single-Arm Phase II Clinical Trial of Fulvestrant Combined with Neoadjuvant Chemotherapy of ER+/HER2- Locally Advanced Breast Cancer: Integrated Analysis of 18F-FES PET-CT and Metabolites with Treatment Response

PURPOSE

This Phase II trial was objected to evaluate the efficacy and safety of adding fulvestrant to neoadjuvant chemotherapy in patients with estrogen receptor (ER)+/human epidermal growth factor receptor 2 (HER2)- locally advanced breast cancer (LABC). Additionally, the study aimed to investigate the association of 16α-18F-fluoro-17β-fluoroestradiol (18F-FES) positron emission tomography (PET)-computed tomography (CT) and metabolites with efficacy.

MATERIALS AND METHODS

Fulvestrant and EC-T regimen were given to ER+/HER2- LABC patients before surgery. At baseline, patients received 18F-FES PET-CT scan, and plasma samples were taken for liquid chromatography-mass spectrometry analysis. The primary endpoint was objective response rate (ORR). Secondary endpoints included total pathologic complete response (tpCR) and safety.

RESULTS

Among the 36 patients enrolled, the ORR was 86.1%, the tpCR rate was 8.3%. The incidence of grade ≥ 3 treatment-emergent adverse events was 22%. The decrease in ER value in sensitive patients was larger than that in non-sensitive patients, as was Ki-67 (p < 0.05). The maximum standardized uptake value, mean standardized uptake values, total lesion ER expression of 18F-FES PET-CT in sensitive patients were significantly higher than those in non-sensitive patients (p < 0.05). Moreover, these parameters were significantly correlated with Miller and Payne grade and the change in ER expression before and after treatment (p < 0.05). Thirteen differential expressed metabolites were identified, which were markedly enriched in 19 metabolic pathways.

CONCLUSION

This regimen demonstrated acceptable toxicity and encouraging antitumor efficacy. 18F-FES PET-CT might serve as a tool to predict the effectiveness of this therapy. Altered metabolites or metabolic pathways might be associated with treatment response.

PET Imaging of Breast Cancer: Current Applications and Future Directions

As molecular imaging use expands for patients with breast cancer, it is important for breast radiologists to have a basic understanding of molecular imaging, including PET. Although breast radiologists may not directly interpret such studies, basic knowledge of molecular imaging will enable the radiologist to better direct diagnostic workup of patients as well as discuss diagnostic imaging with the patient and other treating physicians. Several new tracers are now available to complement imaging glucose metabolism with FDG. Because it provides a noninvasive assessment of disease status across the whole body, PET offers specific advantages over tissue-based assays. Paired with targeted therapy, molecular imaging has the potential to guide personalized treatment of breast cancer, including guiding dosing during drug trials as well as predicting and assessing clinical response. This review discusses the current established applications of FDG, which remains the most widely used PET radiotracer for malignancy, including breast cancer, and highlights potential areas for expanded use based on recent research. It also summarizes research to date on the U.S. Food and Drug Administration (FDA)-approved PET tracer 16α-18F-fluoro-17β-estradiol (FES), which targets ER, including the current guidelines from the Society of Nuclear Medicine and Molecular Imaging on the appropriate use of FES-PET/CT for breast cancer as well as areas of active investigation for other potential applications. Finally, the review highlights several of the most promising novel PET tracers that are poised for clinical translation in the near future.

Update on 18F-Fluoroestradiol

18F-16α-Fluoroestradiol (18F-FES) is a radiolabeled estrogen analogue positron emission tomography (PET) imaging agent that binds to the estrogen receptor (ER) in the nucleus of ER-expressing cells. Proof-of-concept studies of 18F-FES demonstrated expected correlation between tumoral 18F-FES-positivity on PET-imaging and ER+ status assessed on biopsy samples by radioligand binding and immunohistochemistry. After decades of study, 18F-FES PET/CT gained clinical approval in 2016 in France and 2020 in the United States for use in patients with ER+ metastatic or recurrent breast cancer. ER+ as assessed by 18F-FES PET/CT has been shown to serve as a biomarker, identifying metastatic breast cancer patients who may respond to endocrine therapy and those who are unlikely to respond. In 2023, the Society of Nuclear Medicine and Molecular Imaging (SNMMI) published Appropriate Use Criteria for 18F-FES PET/CT, identifying four indications in which use of 18F-FES PET/CT was "appropriate": (1) To assess functional ER status in metastatic lesions unfavorable to biopsy or when biopsy is nondiagnostic, (2) To detect ER status when other imaging tests are equivocal or suspicious, and at (3) initial diagnosis of metastatic disease or (4) progression of metastatic disease, for considering endocrine therapy. This article reviews the foundations of 18F-FES imaging, including normal distribution, false positives, and false negatives, and describes the most up-to-date clinical uses as well as emerging research in breast cancer and other patient populations.

Impact of 18F-FES PET/CT on Clinical Decisions in the Management of Recurrent or Metastatic Breast Cancer

The clinical impact of 16α-18F-fluoro-17β-estradiol (18F-FES) PET/CT on patient management has not been well investigated. The aim of this study was to assess the clinical impact of 18F-FES PET/CT on the management of patients with recurrent or metastatic breast cancer. Methods: Study subjects were identified retrospectively from a database of a prospective trial for postmarketing surveillance of 18F-FES between 2021 and 2023. Patients who were suspected or known to have recurrent or metastatic estrogen receptor-positive breast cancer based on a routine standard workup were included. Planned management before and actual management after 18F-FES PET/CT were assessed by 2 experienced medical oncologists via medical chart review. A 5-point questionnaire was provided to evaluate the value of 18F-FES PET/CT for management planning. The rate of intention-to-treat and interdisciplinary changes, and the impact of 18F-FES PET/CT according to PET/CT result or clinical indication, were examined. Results: Of the 344 included patients, 120 (35%) experienced a change in management after 18F-FES PET/CT. In 139 (40%) patients,18F-FES PET/CT supported the existing management decision without a change in management. Intention-to-treat and interdisciplinary changes accounted for 64% (77/120) and 68% (82/120) of all changes, respectively. A higher rate of change was observed when lesions were 18F-FES-negative (44% [36/81]) than 18F-FES-positive (30% [51/172]) or mixed 18F-FES-positive/negative (36% [33/91]). Regarding clinical indications, the highest rate of change was shown when evaluating the origins of metastasis of double primary cancers (64% [9/14]). Conclusion: 18F-FES PET/CT modified the management of recurrent or metastatic breast cancer, serving as an impactful imaging modality in clinical practice.

Diagnostic Accuracy of 18 F-FES PET/CT for the Detection of Recurrent and Metastatic Breast Cancer

PURPOSE

To evaluate the diagnostic value of 16α- 18 F-fluoro-17β-fluoroestradiol ( 18 F-FES) PET/CT for distant metastasis or recurrence in patients with estrogen receptor (ER)-positive breast cancer.

METHODS

Patients with ER-positive breast cancer and suspected of de novo metastasis or recurrence were retrospectively identified from a prospective cohort enrolled for a postmarketing surveillance study of 18 F-FES at our institution. Per-patient diagnostic accuracy was assessed using pathology or 2 or more standard-of-care imaging procedures with a minimum of 6 months of follow-up as the reference standard. The per-region detection rate of 18 F-FES PET/CT was evaluated and compared with that of standard-of-care imaging.

RESULTS

Of the 162 included patients, 104 and 58 were suspected to have recurrence or de novo metastasis, respectively. The overall sensitivity and specificity of 18 F-FES PET/CT were 95% (95% confidence interval [CI], 89%-98%) and 89% (95% CI, 76%-96%), respectively. When stratified according to clinical settings, the sensitivity and specificity were 95% (95% CI, 88%-99%) and 96% (95% CI, 78%-100%), respectively, for detecting recurrence, and 94% (95% CI, 81%-99%) and 82% (95% CI, 60%-95%) for detecting distant metastasis. In region-based analysis, the overall detection rate of 18 F-FES PET/CT was significantly higher than that of standard-of-care imaging (92% [95% CI, 89%-94%] vs 83% [95% CI, 79%-87%], P < 0.001).

CONCLUSIONS

18 F-FES PET/CT showed excellent diagnostic performance in patients with ER-positive breast cancer suspected of de novo metastasis or recurrence.

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.

Design, Synthesis, and Biological Evaluation of Novel Nonsteroidal 18F-Labeled PET Probes Specifically Targeting Estrogen Receptor α

The estrogen receptor α positive (ERα+) subtype represents nearly 70% of all breast cancers (BCs), which seriously threaten women's health. Positron emission computed tomography (PET) characterizes its superiority in detecting the recurrence and metastasis of BC. In this article, an array of novel PET probes ([18F]R-1, [18F]R-2, [18F]R-3, and [18F]R-4) targeting ERα based on the tetrahydropyridinyl indole scaffold were developed. Among them, [18F]R-3 and [18F]R-4 showed good target specificity toward ERα and could distinguish MCF-7 (ERα+) and MDA-MB-231 (ERα-) tumors efficiently. Especially, [18F]R-3 could differentiate the ERα positive/negative tumors successfully with a higher tumor-to-muscle uptake ratio (T/M) than that of [18F]R-4. The radioactivity of [18F]R-3 in the MCF-7 tumor was 5.24 ± 0.84%ID/mL and its T/M ratio was 2.49 ± 0.62 at 25 min postinjection, which might be the optimal imaging time point in PET scanning. On the contrary, [18F]R-3 did not accumulate in the MDA-MB-231 tumor at all. The autoradiography analysis of [18F]R-3 on the MCF-7 tumor-bearing mice model was consistent with the PET imaging results. [18F]R-3 exhibited the pharmacokinetic property of rapid distribution and slow clearance, making it suitable for use as a diagnostic PET probe. Overall, [18F]R-3 was capable of serving as a PET radiotracer to delineate the ERα+ tumor and was worthy of further exploitation.

Early prediction of endocrine responsiveness in ER+/HER2-negative metastatic breast cancer (MBC): pilot study with 18F-fluoroestradiol (18F-FES) CT/PET

BACKGROUND

18F-fluoroestradiol (FES) positron emission tomography (PET)/computed tomography (CT) is considered an accurate diagnostic tool to determine whole-body endocrine responsiveness. In the endocrine therapy (ET)-FES trial, we evaluated 18F-FES PET/CT as a predictive tool in estrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC).

PATIENTS AND METHODS

Eligible patients underwent an 18F-FES PET/CT at baseline. Patients with standardized uptake value (SUV) ≥ 2 received single-agent ET until progressive disease; patients with SUV < 2 were randomized to single-agent ET (arm A) or chemotherapy (ChT) (arm B). The primary objective was to compare the activity of first-line ET versus ChT in patients with 18F-FES SUV < 2.

RESULTS

Overall, 147 patients were enrolled; 117 presented with 18F-FES SUV ≥ 2 and received ET; 30 patients with SUV < 2 were randomized to ET or ChT. After a median follow-up of 62.4 months, 104 patients (73.2%) had disease progression and 53 died (37.3%). Median progression-free survival (PFS) was 12.4 months [95% confidence interval (CI) 3.1-59.6 months] in patients with SUV < 2 randomized to arm A versus 23.0 months (95% CI 7.7-30.0 months) in arm B, [hazard (HR) = 0.71, 95% CI 0.3-1.7 months]; median PFS was 18.0 months (95% CI 11.2-23.1 months) in patients with SUV ≥ 2 treated with ET. Median overall survival (OS) was 28.2 months (95% CI 14.2 months-not estimable) in patients with SUV < 2 randomized to ET (arm A) versus 52.8 months (95% CI 16.2 months-not estimable) in arm B (ChT). Median OS was not reached in patients with SUV ≥ 2. 60-month OS rate was 41.6% (95% CI 10.4% to 71.1%) in arm A, 42.0% (95% CI 14.0% to 68.2%) in arm B, and 59.6% (95% CI 48.6% to 69.0%) in patients with SUV ≥ 2. In patients with SUV ≥ 2, 60-month OS rate was 72.6% if treated with aromatase inhibitors (AIs) versus 40.6% in case of fulvestrant or tamoxifen (P < 0.005).

CONCLUSIONS

The ET-FES trial demonstrated that ER+/HER2- MBC patients are a heterogeneous population, with different levels of endocrine responsiveness based on 18F-FES CT/PET SUV.

Clinical and economic outcomes of adding [18F]FES PET/CT in estrogen receptor status identification in metastatic and recurrent breast cancer in the US

BACKGROUND AND OBJECTIVES

Correct identification of estrogen receptor (ER) status in breast cancer (BC) is crucial to optimize treatment; however, standard of care, involving biopsy and immunohistochemistry (IHC), and other diagnostic tools such as 2-deoxy-2-[18F]fluoro-D-glucose or 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG), can yield inconclusive results. 16α-[18F]fluoro-17β-fluoroestradiol ([18F]FES) can be a powerful tool, providing high diagnostic accuracy of ER-positive disease. The aim of this study was to estimate the budget impact and cost-effectiveness of adding [18F]FES PET/CT to biopsy/IHC in the determination of ER-positive status in metastatic (mBC) and recurrent breast cancer (rBC) in the United States (US).

METHODS

An Excel-based decision tree, combined with a Markov model, was developed to estimate the economic consequences of adding [18F]FES PET/CT to biopsy/IHC for determining ER-positive status in mBC and rBC over 5 years. Scenario A, where the determination of ER-positive status is carried out solely through biopsy/IHC, was compared to scenario B, where [18F]FES PET/CT is used in addition to biopsy/IHC.

RESULTS

The proportion of true positive and true negative test results increased by 0.2 to 8.0 percent points in scenario B compared to scenario A, while re-biopsies were reduced by 94% to 100%. Scenario B resulted in cost savings up to 142 million dollars.

CONCLUSIONS

Adding [18F]FES PET/CT to biopsy/IHC may increase the diagnostic accuracy of the ER status, especially when a tumor sample cannot be obtained, or the risk of a biopsy-related complication is high. Therefore, adding [18F]FES PET/CT to biopsy/IHC would have a positive impact on US clinical and economic outcomes.

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.

Quarter-Century Transformation of Oncology: Positron Emission Tomography for Patients with Breast Cancer

PET radiotracers have become indispensable in the care of patients with breast cancer. 18F-fluorodeoxyglucose has become the preferred method of many oncologists for systemic staging of breast cancer at initial diagnosis, detecting recurrent disease, and for measuring treatment response after therapy. 18F-Sodium Fluoride is valuable for detection of osseous metastases. 18F-fluoroestradiol is now FDA-approved with multiple appropriate clinical uses. There are multiple PET radiotracers in clinical trials, which may add utility of PET imaging for patients with breast cancer in the future. This article will describe the advances during the last quarter century in PET for patients with breast cancer.

Innovations in Positron Emission Tomography and State of the Art in the Evaluation of Breast Cancer Treatment Response

The advent of hybrid Positron Emission Tomography/Computed Tomography (PET/CT) and PET/Magnetic Resonance Imaging (MRI) scanners resulted in an increased clinical relevance of nuclear medicine in oncology. The use of [18F]-Fluorodeoxyglucose ([18F]FDG) has also made it possible to study tumors (including breast cancer) from not only a dimensional perspective but also from a metabolic point of view. In particular, the use of [18F]FDG PET allowed early confirmation of the efficacy or failure of therapy. The purpose of this review was to assess the literature concerning the response to various therapies for different subtypes of breast cancer through PET. We start by summarizing studies that investigate the validation of PET/CT for the assessment of the response to therapy in breast cancer; then, we present studies that compare PET imaging (including PET devices dedicated to the breast) with CT and MRI, focusing on the identification of the most useful parameters obtainable from PET/CT. We also focus on novel non-FDG radiotracers, as they allow for the acquisition of information on specific aspects of the new therapies.

ER status conversion and subsequent treatment: an assessment of negative ER expression detected by 18F-FES PET in metastatic breast cancer patients with ER-positive primary tumors

Background

The 18F-fluoroestradiol positron emission tomography/computed tomography (18F-FES PET/CT) technique provides a convenient method to evaluate the overall estrogen receptor (ER) expression in metastatic breast cancer (MBC) patients. There are long debates on the characteristics and treatment strategy of patients with positive primary ER lesions but negative ER expression in metastatic disease. 18F-FES PET offers an opportunity to answer this question.

Objectives

This study aimed to characterize the primary ER-positive patients with advanced-stage FES negativity and investigate the real-world treatment decisions made by physicians subsequently, and compare the efficacy between different regimens.

Design

This observational cohort study was conducted at Fudan University Shanghai Cancer Center, enrolling breast cancer patients with ER-positive primary tumors who showed advanced-stage FES negativity.

Methods

Descriptive statistics were used in clinicopathologic characteristics and compared with a chi-square test or t-test. In addition, progression-free survival (PFS) was estimated by the Kaplan-Meier method and compared by log-rank test.

Results

16.6% (52/314) of patients with an ER-positive primary tumor had negative ER expression assessed by 18F-FES for MBC prior to receiving first-line systemic therapy, among whom adjuvant endocrine therapy was prevalently utilized (86.5%, 45/52). The rate of FES negativity in the advanced stage was negatively correlated with levels of ER expression of primary tumors. Chemotherapy (83.3%, 40/48) was the most common treatment strategy afterward, among which capecitabine monotherapy (62.5%, 25/40) was a dominant alternative. PFS was significantly prolonged with capecitabine alone versus other chemotherapy (median PFS: 13.14 versus 6.21 months, p = 0.029).

Conclusion

Negative conversion of ER in MBC detected by 18F-FES occurred frequently. Patients with lower ER expression in the primary lesion were more likely to have negative ER expression in the metastasis. In real-world clinical practice, most physicians primarily opted for chemotherapy, with capecitabine monotherapy being a commonly selected regimen.

Trial registration

ClinicalTrials.gov identifier: NCT05797987.

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.

Estrogen Receptor-Targeted and Progesterone Receptor-Targeted PET for Patients with Breast Cancer

Estrogen receptor (ER)-targeted imaging with 16α-18F-fluoro-17β-fluoroestradiol (18F-FES) has multiple proven clinical applications for patients with ER-positive breast cancer, including helping to select optimal patients for endocrine therapies, assessing ER status in lesions that are difficult to biopsy, and evaluating lesions with inconclusive results on other imaging tests. This has led to US Food and Drug Administration approval of 18F-FES PET for patients with ER-positive breast cancer. Newer progesterone receptor-targeted imaging agents are in clinical trials.

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.

18F-Fluoroestradiol: Current Applications and Future Directions

In the United States, breast cancer is the second leading cause of cancer death in all women and the leading cause of cancer death in Black women. The breast cancer receptor profile, assessed with immunohistochemical staining of tissue samples, allows prediction of outcomes and direction of patient treatment. Approximately 80% of newly diagnosed breast cancers are hormone receptor (HR) positive, which is defined as estrogen receptor (ER) and/or progesterone receptor (PR) positive. Patients with ER-positive disease can be treated with therapies targeting the ER; however, the assessment of ER expression with immunohistochemical staining of biopsy specimens has several limitations including sampling error, false-negative results, challenging or inaccessible biopsy sites, and the inability to synchronously and serially assess all metastatic sites to identify spatial and/or temporal ER heterogeneity. In May 2020, after decades of research, the U.S. Food and Drug Administration approved the PET radiotracer fluorine 18 (¹⁸F) fluoroestradiol (FES) for clinical use in patients with ER-positive recurrent or metastatic breast cancer as an adjunct to biopsy. FES binds to the ER in the nucleus of ER-expressing cells, enabling whole-body in vivo assessment of ER expression. This article is focused on the approved uses of FES in the United States, including identification of a target lesion for confirmatory biopsy, in vivo assessment of biopsy-proven ER-positive disease, and evaluation of spatial and temporal ER heterogeneity. FES is an example of precision medicine that has been leveraged to optimize the care of patients with breast cancer. ^© RSNA, 2023 See the invited commentary by Fowler in this issue. Quiz questions for this article are available through the Online Learning Center.

Molecular and functional imaging in cancer-targeted therapy: current applications and future directions

Targeted anticancer drugs block cancer cell growth by interfering with specific signaling pathways vital to carcinogenesis and tumor growth rather than harming all rapidly dividing cells as in cytotoxic chemotherapy. The Response Evaluation Criteria in Solid Tumor (RECIST) system has been used to assess tumor response to therapy via changes in the size of target lesions as measured by calipers, conventional anatomically based imaging modalities such as computed tomography (CT), and magnetic resonance imaging (MRI), and other imaging methods. However, RECIST is sometimes inaccurate in assessing the efficacy of targeted therapy drugs because of the poor correlation between tumor size and treatment-induced tumor necrosis or shrinkage. This approach might also result in delayed identification of response when the therapy does confer a reduction in tumor size. Innovative molecular imaging techniques have rapidly gained importance in the dawning era of targeted therapy as they can visualize, characterize, and quantify biological processes at the cellular, subcellular, or even molecular level rather than at the anatomical level. This review summarizes different targeted cell signaling pathways, various molecular imaging techniques, and developed probes. Moreover, the application of molecular imaging for evaluating treatment response and related clinical outcome is also systematically outlined. In the future, more attention should be paid to promoting the clinical translation of molecular imaging in evaluating the sensitivity to targeted therapy with biocompatible probes. In particular, multimodal imaging technologies incorporating advanced artificial intelligence should be developed to comprehensively and accurately assess cancer-targeted therapy, in addition to RECIST-based methods.

State of the Art in 2022 PET/CT in Breast Cancer: A Review

Molecular imaging with positron emission tomography is a powerful and well-established tool in breast cancer management. In this review, we aim to address the current place of the main PET radiopharmaceuticals in breast cancer care and offer perspectives on potential future radiopharmaceutical and technological advancements. A special focus is given to the following: the role of 18F-fluorodeoxyglucose positron emission tomography in the clinical management of breast cancer patients, especially during staging; detection of recurrence and evaluation of treatment response; the role of 16α-18Ffluoro-17β-oestradiol positron emission tomography in oestrogen receptors positive breast cancer; the promising radiopharmaceuticals, such as 89Zr-trastuzumab and 68Ga- or 18F-labeled fibroblast activation protein inhibitor; and the application of artificial intelligence.

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 [...].

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.

Evaluation of tumour heterogeneity by 18F-fluoroestradiol PET as a predictive measure in breast cancer patients receiving palbociclib combined with endocrine treatment

Background

Predictive biomarkers are needed to identify oestrogen receptor-positive, human epidermal growth factor receptor 2-negative (ER + /HER2-) metastatic breast cancer (MBC) patients who would likely benefit from cyclin-dependent kinase 4 and 6 inhibitors combined with endocrine therapy. Therefore, we performed an exploratory study to evaluate the tumour heterogeneity parameters based on 16α-¹⁸F-fluoro-17β-oestradiol (¹⁸F-FES)-PET imaging as a potential marker to predict progression-free survival (PFS) in MBC patients receiving palbociclib combined with endocrine therapy.

Methods

Fifty-six ER + MBC patients underwent ¹⁸F-FES-PET/CT before the initiation of palbociclib. ¹⁸F-FES uptake was quantified and expressed as the standardized uptake value (SUV). Interlesional heterogeneity was qualitatively identified according to the presence or absence of ¹⁸F-FES-negative lesions. Intralesional heterogeneity was measured by the SUV-based heterogeneity index (HI = SUVmax/SUVmean). Association with survival was evaluated using the Cox proportional hazards model.

Results

A total of 551 metastatic lesions were found in 56 patients: 507 lesions were identified as ¹⁸F-FES-positive, 38 lesions were distributed across 10 patients without ¹⁸F-FES uptake, and the remaining 6 were liver lesions. Forty-three patients obtained a clinical benefit, and 13 developed progressive disease (PD) within 24 weeks. Nine out of 10 patients with an ¹⁸F-FES-negative site developed PD, and the median PFS was only 2.4 months. Among 46 patients with only ¹⁸F-FES-positive lesions, only four patients had PD, and the median PFS was 23.6 months. There were statistically significant differences between the two groups (P < 0.001). For the subgroup of patients with only ¹⁸F-FES-positive lesions, low FES-HI patients experienced substantially longer PFS times than those with high FES-HI (26.5 months vs. 16.5 months, P = 0.004).

Conclusions

¹⁸F-FES-PET may provide a promising method for identifying and selecting candidate ER + /HER2- MBC patients who would most likely benefit from palbociclib combined with endocrine treatment and could serve as a predictive marker for treatment response.

Trial registration NCT04992156, Date of registration: August 5, 2021 (retrospectively registered).

Circulating tumor DNA for breast cancer: Review of active clinical trials

BACKGROUND

The new diagnostic concept of liquid biopsy is based on the analysis of circulating tumor cells (CTCs) and cell-free DNA (ctDNA). In addition to providing a more comprehensive view of the tumor characteristics including molecular variations, ctDNA analysis through liquid biopsies may also allow for a non-invasive, rapid, and cost-effective identification of biomarkers for tumor detection and monitoring of tumor progression.

OBJECTIVE

In this review, we summarize key active clinical trial studies involving utilization of ctDNA derived from liquid biopsy in the early and metastatic breast cancer setting. With this, we also provide a brief overview of the potential future implementations of the LB technology and outlining how ctDNA analysis needs to be standardized through the performance of similar clinical studies.

METHODS

A review was conducted on Clinicaltrials.gov to identify active trials related to use of circulating tumor DNA (ctDNA) for breast cancer. Search terms included "breast cancer," "liquid biopsy," and "ctDNA."

CONCLUSION

While LB is gaining traction in many cancer settings, its use in BC is still early and warrants more investigation in breast cancer diagnostic and treatment settings, including early detection of disease recurrence.

Novel applications of molecular imaging to guide breast cancer therapy

The goals of precision oncology are to provide targeted drug therapy based on each individual’s specific tumor biology, and to enable the prediction and early assessment of treatment response to allow treatment modification when necessary. Thus, precision oncology aims to maximize treatment success while minimizing the side effects of inadequate or suboptimal therapies. Molecular imaging, through noninvasive assessment of clinically relevant tumor biomarkers across the entire disease burden, has the potential to revolutionize clinical oncology, including breast oncology. In this article, we review breast cancer positron emission tomography (PET) imaging biomarkers for providing early response assessment and predicting treatment outcomes. For 2-¹⁸fluoro-2-deoxy-D-glucose (FDG), a marker of cellular glucose metabolism that is well established for staging multiple types of malignancies including breast cancer, we highlight novel applications for early response assessment. We then review current and future applications of novel PET biomarkers for imaging the steroid receptors, including the estrogen and progesterone receptors, the HER2 receptor, cellular proliferation, and amino acid metabolism.

Clinical Validity of 16α-[18F]Fluoro-17β-Estradiol Positron Emission Tomography/Computed Tomography to Assess Estrogen Receptor Status in Newly Diagnosed Metastatic Breast Cancer

PURPOSE

Determining the estrogen receptor (ER) status is essential in metastatic breast cancer (MBC) management. Whole-body ER imaging with 16α-[¹⁸F]fluoro-17β-estradiol positron emission tomography ([¹⁸F]FES-PET) is increasingly used for this purpose. To establish the clinical validity of the [¹⁸F]FES-PET, we studied the diagnostic accuracy of qualitative and quantitative [¹⁸F]FES-PET assessment to predict ER expression by immunohistochemistry in a metastasis.

METHODS

In a prospective multicenter trial, 200 patients with newly diagnosed MBC underwent extensive workup including molecular imaging. For this subanalysis, ER expression in the biopsied metastasis was related to qualitative whole-body [¹⁸F]FES-PET evaluation and quantitative [¹⁸F]FES uptake in the corresponding metastasis. A review and meta-analysis regarding [¹⁸F]FES-PET diagnostic performance were performed.

RESULTS

Whole-body [¹⁸F]FES-PET assessment predicted ER expression in the biopsied metastasis with good accuracy: a sensitivity of 95% (95% CI, 89 to 97), a specificity of 80% (66 to 89), a positive predictive value (PPV) of 93% (87 to 96), and a negative predictive value (NPV) of 85% (72 to 92) in 181 of 200 evaluable patients. Quantitative [¹⁸F]FES uptake predicted ER immunohistochemistry in the corresponding metastasis with a sensitivity/specificity of 91%/69% and a PPV/NPV of 90%/71% in 156 of 200 evaluable patients. For bone metastases, PPV/NPV was 92%/81%. Meta-analysis with addition of our data has increased diagnostic performance and narrowed the 95% CIs compared with previous studies with a sensitivity/specificity of both 86% (81 to 90 and 73 to 93, respectively).

CONCLUSION

In this largest prospective series so far, we established the clinical validity of [¹⁸F]FES-PET to determine tumor ER status in MBC. In view of the high diagnostic accuracy of qualitatively assessed whole-body [¹⁸F]FES-PET, this noninvasive imaging modality can be considered a valid alternative to a biopsy of a metastasis to determine ER status in newly MBC (ClinicalTrials.gov identifier: NCT01957332).

Ribociclib Cytotoxicity Alone or Combined With Progesterone and/or Mitotane in in Vitro Adrenocortical Carcinoma Cells

Mitotane is the only approved drug for treating adrenocortical carcinoma (ACC). The regimen added to mitotane is chemotherapy with etoposide, doxorubicin, and cisplatin. This pharmacological approach, however, has a limited efficacy and significant toxicity. Target-therapy agents represent a new promising approach to cancer therapy. Among these, a preeminent role is played by agents that interfere with cell-cycle progression, such as CDK4/6-inhibitors. Here, we investigate whether ribociclib could induce a cytotoxic effect both in ACC cell line and patient-derived primary cell cultures, alone or in combined settings. Cell viability was determined by 3-(4,5-dimethyl-2-thiazol)-2,5-diphenyl-2H-tetrazolium bromide assay, whereas cell proliferation was evaluated by direct count. Binary combination experiments were performed using Chou and Talalay method. Gene expression was analyzed by quantitative RT-PCR, whereas protein expression was evaluated by immunofluorescence. A double staining assay revealed that ribociclib induced a prevalent apoptotic cell death. Cell-cycle analysis was performed to evaluate the effect of ribociclib treatment on cell-cycle progression in ACC cell models. Our results indicate that ribociclib was cytotoxic and reduced the cell proliferation rate. The effect on cell viability was enhanced when ribociclib was combined with progesterone and/or mitotane. The effect of ribociclib on cell-cycle progression revealed a drug-induced cell accumulation in G2 phase. The positive relationship underlined by our results between ribociclib, progesterone, and mitotane strengthen the clinical potential of this combination.

Gastrin-Releasing Peptide Receptor Antagonist [68Ga]RM2 PET/CT for Staging of Pre-Treated, Metastasized Breast Cancer

BACKGROUND

Positron emission tomography (PET)/computed tomography (CT) using the gastrin-releasing peptide receptor antagonist [⁶⁸Ga]RM2 has shown to be a promising imaging method for primary breast cancer (BC) with positive estrogen receptor (ER) status. This study assessed tumor visualization by [⁶⁸Ga]RM2 PET/CT in patients with pre-treated ER-positive BC and suspected metastases.

METHODS

This retrospective pilot study included eight female patients with initial ER-positive, pre-treated BC who underwent [⁶⁸Ga]RM2 PET/CT. Most of these patients (seven out of eight; 88%) were still being treated with or had received endocrine therapy. [⁶⁸Ga]RM2 PET/CTs were visually analyzed by two nuclear medicine specialists in consensus. Tumor manifestations were rated qualitatively (i.e., RM2-positive or RM2-negative) and quantitatively using the maximum standardized uptake value (SUVmax). SUVmax values were compared between the two subgroups (RM2-positive vs. RM2-negative).

RESULTS

Strong RM2 binding was found in all metastatic lesions of six patients (75%), whereas tracer uptake in all metastases of two patients (25%) was rated negative. Mean SUVmax of RM2-positive metastases with the highest SUVmax per patient (in lymph node and bone metastases; 15.8 ± 15.1 range: 3.7-47.8) was higher than mean SUVmax of the RM2-negative metastases with the highest SUVmax per patient (in bone metastases; 1.6 ± 0.1, range 1.5-1.7).

CONCLUSIONS

Our data suggest that RM2 binding is maintained in the majority of patients with advanced disease stage of pre-treated ER-positive BC. Thus, [⁶⁸Ga]RM2 PET/CT could support treatment decision in these patients, radiotherapy planning in oligometastatic patients or selection of patients for RM2 radioligand therapy. Further studies with larger patient cohorts are warranted to confirm these findings.

Safety and Effectiveness of F-18 Fluoroestradiol Positron Emission Tomography/Computed Tomography: a Systematic Review and Meta-analysis

BACKGROUND

We conducted a pooled analysis of the diagnostic accuracy of F-18 fluoroestradiol (F-18 FES) positron emission tomography/computed tomography (PET/CT) assessing estrogen receptor expression of patients who have recurrent or metastatic breast cancer.

METHODS

Two investigators and seven related experts (from the departments of nuclear medicine, hematological oncology, surgery, and evidence-based medicine) evaluated the effectiveness of F-18 FES PET/CT according to diagnostic accuracy and correlation with immunohistochemistry tests via systematic literature review, and safety according to test-related side effects. The present study was conducted in accordance with the Scottish Intercollegiate Guidelines (SIGN), and the Cochrane, and Preferred Reporting Items for Systematic Reviews and Meta Analyses guidelines. The SIGN tools were used for quality assessment.

RESULTS

Of the 512 articles retrieved in the literature search, 8 were deemed to be eligible for inclusion. Results of the evaluation indicated that the F-18 FES PET/CT test was safe because patients who reported pain in the injection site in the analyzed articles are most likely to be caused by mechanical injury from needle injection not by administration of radioactive materials. Assessment of diagnostic accuracy based on data from seven studies revealed a pooled sensitivity and specificity of 0.86 and 0.85, respectively.

CONCLUSION

As such, the test was evaluated to be a safe and effective and, considering the anatomical site where only invasive tests are possible, the test was deemed to have high clinical utility.

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.

The clinical value of 18F-fluoroestradiol in assisting individualized treatment decision in dual primary malignancies

Background

For patients with previously diagnosed dual primary tumors, it is usually difficult to determine the diagnosis and treatment of stage IV recurrence. The study was to explore the influences of ¹⁸F-fluoroestradiol positron emission tomography/computed tomography (¹⁸F-FES PET/CT) in the diagnosis of estrogen receptor (ER) positive breast cancer combined with other primary tumor with distant metastases.

Methods

Multidisciplinary team were organized to explore the definite clinical value of ¹⁸F-FES PET/CT in stage IV patients suffered from ER-positive breast cancer and another primary tumor synchronously or metachronously. Thirty-two female patients were retrospectively analyzed who underwent ¹⁸F-FES PET/CT scans in our center. Before and after reading ¹⁸F-FES reports, the team members from department of surgery, oncology and radiotherapy should make decisions of management strategy.

Results

Totally, the multidisciplinary team completed the management decision-making of the 32 patients before and after ¹⁸F-FES PET/CT scans. 87.5% (n=28) of the patients were considered to benefit from ¹⁸F-FES reports for diagnosis and treatment decisions. Out of the 28 patients, 7 patients (7/32, 21.9%) were considered to definitely change the management strategies while 12 patients (12/32, 37.5%) was instructive to develop management plans after the scan. The other 9 patients were suggested reassuring decision-making process by ¹⁸F-FES PET/CT.

Conclusions

¹⁸F-FES PET/CT scans have clinical effects on diagnosis and treatment strategies of stage IV patients suffered from ER-positive breast cancer and another primary tumor.

Value of 18F-FES PET in Solving Clinical Dilemmas in Breast Cancer Patients: A Retrospective Study

Breast cancer (BC) is a heterogeneous disease in which estrogen receptor (ER) expression plays an important role in most tumors. A clinical dilemma may arise when a metastasis biopsy to determine the ER status cannot be performed safely or when ER heterogeneity is suspected between tumor lesions. Whole-body ER imaging, such as 16α-18F-fluoro-17β-estradiol (18F-FES) PET, may have added value in these situations. However, the role of this imaging technique in routine clinical practice remains to be further determined. Therefore, we assessed whether the physician's remaining clinical dilemma after the standard workup was solved by the 18F-FES PET scan. Methods: This retrospective study included 18F-FES PET scans of patients who had (or were suspected to have) ER-positive metastatic BC and for whom a clinical dilemma remained after the standard workup. The scans were performed at the University Medical Center of Groningen between November 2009 and January 2019. We investigated whether the physician's clinical dilemma was solved, defined either as solving the clinical dilemma through the 18F-FES PET results or as basing a treatment decision directly on the 18F-FES PET results. In addition, the category of the clinical dilemma was reported, as well as the rate of 18F-FES-positive or -negative PET scans, and any correlation to the frequency of solved dilemmas was determined. Results: One hundred 18F-FES PET scans were performed on 83 patients. The clinical dilemma categories were inability to determine the extent of metastatic disease or suspected metastatic disease with the standard workup (n = 52), unclear ER status of the tumor (n = 31), and inability to determine which primary tumor caused the metastases (n = 17). The dilemmas were solved by 18F-FES PET in 87 of 100 scans (87%). In 81 of 87 scans, a treatment decision was based directly on 18F-FES PET results (treatment change, 51 scans; continuance, 30 scans). The frequency of solved dilemmas was not related to the clinical dilemma category (P = 0.334). However, the frequency of solved dilemmas was related to whether scans were 18F-FES-positive (n = 63) or 18F-FES-negative (n = 37; P < 0.001). Conclusion: For various indications, the 18F-FES PET scan can help to solve most clinical dilemmas that may remain after the standard workup. Therefore, the 18F-FES PET scan has added value in BC patients who present the physician with a clinical dilemma.

PET Imaging for Breast Cancer

Imaging plays an integral role in the clinical care of patients with breast cancer. This review article focuses on the use of PET imaging for breast cancer, highlighting the clinical indications and limitations of 2-deoxy-2-[¹⁸F]fluoro-d-glucose (FDG) PET/CT, the potential use of PET/MRI, and 16α-[¹⁸F]fluoroestradiol (FES), a newly approved radiopharmaceutical for estrogen receptor imaging.

Whole-Body Characterization of Estrogen Receptor Status in Metastatic Breast Cancer with 16α-18F-Fluoro-17β-Estradiol Positron Emission Tomography: Meta-Analysis and Recommendations for Integration into Clinical Applications

Estrogen receptor (ER) status by immunohistochemistry (IHC) of cancer tissue is currently used to direct endocrine therapy in breast cancer. Positron emission tomography (PET) with 16α-18F-fluoro-17β-estradiol (18 F-FES) noninvasively characterizes ER ligand-binding function of breast cancer lesions. Concordance of imaging and tissue assays should be established for 18 F-FES PET to be an alternative or complement to tissue biopsy for metastatic lesions. We conducted a meta-analysis of published results comparing 18 F-FES PET and tissue assays of ER status in patients with breast cancer. PubMed and EMBASE were searched for English-language manuscripts with at least 10 patients and low overall risk of bias. Thresholds for imaging and tissue classification could differ between studies but had to be clearly stated. We used hierarchical summary receiver-operating characteristic curve models for the meta-analysis. The primary analysis included 113 nonbreast lesions from 4 studies; an expanded analysis included 327 total lesions from 11 studies. Treating IHC results as the reference standard, sensitivity was 0.78 (95% confidence region 0.65-0.88) and specificity 0.98 (0.65-1.00) for the primary analysis of nonbreast lesions. In the expanded analysis including non-IHC tissue assays and all lesion sites, sensitivity was 0.81 (0.73-0.87) and specificity 0.86 (0.68-0.94). These results suggest that 18 F-FES PET is useful for characterization of ER status of metastatic breast cancer lesions. We also review current best practices for conducting 18 F-FES PET scans. This imaging assay has potential to improve clinically relevant outcomes for patients with (historically) ER-positive metastatic breast cancer, including those with brain metastases and/or lobular histology. IMPLICATIONS FOR PRACTICE: 16α-18F-fluoro-17β-estradiol positron emission tomography (18 F-FES PET) imaging assesses estrogen receptor status in breast cancer in vivo. This work reviews the sensitivity and specificity of 18 F-FES PET in a meta-analysis with reference tissue assays and discusses best practices for use of the tracer as an imaging biomarker. 18 F-FES PET could enhance breast cancer diagnosis and staging as well as aid in therapy selection for patients with metastatic disease. Tissue sampling limitations, intrapatient heterogeneity, and temporal changes in molecular markers make it likely that 18 F-FES PET will complement existing assays when clinically available in the near future.

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

Background: High physiological 16α-[¹⁸F]-fluoro-17β-estradiol ([¹⁸F]-FES) uptake in the abdomen is a limitation of this positron emission tomography (PET) tracer. Therefore, we investigated the effect of food intake prior to PET acquisition on abdominal background activity in [¹⁸F]-FES-PET scans. Methods: Breast cancer patients referred for [¹⁸F]-FES-PET were included. Three groups were designed: (1) patients who consumed a chocolate bar (fatty meal) between tracer injection and imaging (n = 20), (2) patients who fasted before imaging (n = 20), and (3) patients without diet restrictions (control group, n = 20). We compared the physiological [¹⁸F]-FES uptake, expressed as mean standardized uptake value (SUV_mean), in the abdomen between groups. Results: A significant difference in [¹⁸F]-FES uptake in the gall bladder and stomach lumen was observed between groups, with the lowest values for the chocolate group and highest for the fasting group (p = 0.015 and p = 0.011, respectively). Post hoc analysis showed significant differences in the SUVmean of these organs between the chocolate and fasting groups, but not between the chocolate and control groups. Conclusion: This exploratory study showed that, compared to fasting, eating chocolate decreases physiological gall bladder and stomach [¹⁸F]-FES uptake; further reduction through a normal diet was not seen. A prospective study is warranted to confirm this finding.

Longitudinal Molecular Imaging of Progesterone Receptor Reveals Early Differential Response to Endocrine Therapy in Breast Cancer with an Activating ESR1 Mutation

Activating mutations in the estrogen receptor (ER) α-gene (ESR1) result in constitutive transcriptional activity in the absence of estrogen and are associated with endocrine resistance in metastatic ER-positive (+) breast cancer. It is not known how activating ESR1 mutations may alter the predictive values of molecular imaging agents for endocrine therapy response. This study investigated the effect of an activating ESR1 mutation on pretreatment ¹⁸F-fluoroestradiol (¹⁸F-FES) uptake and early assessment of endocrine therapy response using ¹⁸F-FDG and ¹⁸F-fluorofuranylnorprogesterone (¹⁸F-FFNP) PET/CT imaging of tumor glucose metabolism and progesterone receptor (PR) expression, respectively. Methods: ER+, PR+ T47D breast cancer cells expressing wild-type (WT) ER or an activating ESR1 mutation, Y537S-ER, were used to generate tumor xenografts in ovariectomized female immunodeficient mice supplemented with 17β-estradiol. Tumor growth curves were determined in the presence or absence of estrogen and for ethanol vehicle control or fulvestrant treatment, a selective ER degrader. Pretreatment ¹⁸F-FES uptake was compared between Y537S-ER and WT-ER tumors. Longitudinal PET/CT imaging with ¹⁸F-FFNP and ¹⁸F-FDG was performed before and 7-9 d after the start of endocrine therapy with fulvestrant. Radiopharmaceutical uptake in Y537S-ER and WT-ER tumors was compared between baseline and follow-up scans. Statistical significance was determined using paired t testing for longitudinal imaging and 2-way ANOVA for the ¹⁸F-FFNP tissue biodistribution assay. Results: Y537S-ER xenografts showed estrogen-independent growth, whereas WT-ER tumors grew only with estrogen. Fulvestrant treatment for 28 d significantly reduced tumor volumes for WT-ER but only stabilized volumes for Y537S-ER. Baseline ¹⁸F-FES uptake did not significantly differ between WT-ER and Y537S-ER tumors. Fulvestrant treatment induced a similar early metabolic response for both WT-ER and Y537S-ER tumors. ¹⁸F-FFNP uptake in WT-ER tumors was significantly reduced after 7 d of fulvestrant treatment; however, this reduction did not occur in Y537S-ER tumors, which showed no significant change between baseline and follow-up PET/CT. Conclusion: Molecular imaging of PR expression dynamics could be a noninvasive approach for early identification of reduced effectiveness of endocrine therapy resulting from activating ESR1 mutations.