Comparison of diagnostic sensitivity of [18F]fluoroestradiol and [18F]fluorodeoxyglucose positron emission tomography/computed tomography for breast cancer recurrence in patients with a history of estrogen receptor-positive primary breast cancer

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.

Collagen Vascular Disease-Associated Interstitial Pneumonia With Accumulation of 18F-fluoroestradiol

18F-fluoroestradiol (18F-FES) is a PET radiotracer that binds to the estrogen receptor (ER) in the nucleus of ER-expressing cells and is increasingly used clinically in breast cancer patients to visualize ER expression in lesions. Although 18F-FES accumulation is generally specific, radiation-induced pneumonitis can produce false-positive results, but the underlying mechanisms remain largely unclear. Here, we report the case of a 72-year-old woman with known collagen vascular disease-associated interstitial pneumonia and the accumulation of 18F-FES on 18F-FES-PET/CT, which was conducted to investigate suspected recurrent breast cancer.

The Diagnostic Accuracy of 18F-FDG PET and 18F-FES PET for Staging Grade 1-2 Estrogen Receptor-Positive Breast Cancer

Background According to current guidelines, staging of patients with locally advanced breast cancer and local-regional recurrent breast cancer is preferably performed with PET using 2-fluorine 18-fluoro-2-deoxy-d-glucose (18F-FDG). However, 18F-FDG PET might underperform in low-grade estrogen receptor (ER)-positive breast cancer. Alternatively, 16α-18F-fluoro-17β-estradiol (18F-FES) has emerged as a powerful tracer for in vivo visualization of ER-positive lesions. Purpose To assess whether 18F-FES PET improves staging of grade 1 or 2 ER-positive breast cancer compared with 18F-FDG PET. Materials and Methods Patients with clinical stage II/III or local-regional recurrent, grade 1 or 2, ER-positive breast cancer were included between December 2018 and January 2021 in this prospective multicenter pilot study. All participants underwent an 18F-FES PET examination in addition to standard staging with conventional imaging and 18F-FDG PET. Both PET scans were independently assessed. The disease stage was determined independently based on conventional imaging and 18F-FDG PET or 18F-FES PET. Relevant lesions suspected of malignancy were verified histopathologically, after which a final stage was determined. Results A total of 41 female participants (median age, 56 years [IQR, 48-71 years]) with 44 breast tumors were included. Overall, 29 of 41 participants (71%) were correctly staged at 18F-FDG PET compared with 34 of 41 (83%) at 18F-FES PET (P = .18). Seven of 10 and nine of 10 cases of lobular breast cancer were correctly staged at 18F-FDG and 18F-FES PET, respectively (70% vs 90%; P = .38) and seven of 12 and 11 of 12 cases of grade 1 tumors, respectively (58% vs 92%; P = .06). Regional lymph nodes were incorrectly staged at 18F-FDG PET in six of 44 cases (14%), whereas all cases were correctly staged at 18F-FES PET (P = .02). Both imaging methods had a sensitivity of 100% (95% CI: 59, 100) and a specificity of 91% (95% CI: 76, 98) for the detection of metastatic disease. Conclusion In this prospective pilot study, there was no evidence of a difference in diagnostic accuracy of 18F-FES PET and 18F-FDG PET in staging patients with grade 1 or 2 ER-positive breast cancer. Clinical trial registration no. NCT03726931 Published under a CC BY 4.0 license Supplemental material is available for this article. See also the editorial by Fowler in this issue.

[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.

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.

Development of a Novel Peptide-Based PET Tracer [68Ga]Ga-DOTA-BP1 for BCMA Detection in Multiple Myeloma

B-cell maturation antigen (BCMA) has emerged as a promising tumor marker for the diagnosis and treatment of multiple myeloma. The noninvasive and rapid detection of BCMA expression in vivo provides significant value in screening and evaluating multiple myeloma patients receiving BCMA-targeted therapy. We identified the BCMA-targeting peptide BP1 from a one-bead-one-compound (OBOC) peptide library using a high-throughput microarray strategy. The BCMA-targeting specificity and affinity of BP1 were assessed by surface plasmon resonance imaging (SPRi), flow cytometry, and confocal imaging. BCMA-positive (H929) and BCMA-negative (K562) subcutaneous tumor models were established and labeled with 68Ga for BP1, followed by PET imaging and biodistribution studies. PET imaging demonstrated that 68Ga-labeled BP1 has significant specific uptake in multiple myeloma, enabling rapid identification of BCMA expression and precise delineation of the disease. Thus, BP1 represents an ideal candidate for multiple myeloma imaging.

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.

Dynamic whole-body [18F]FES PET/CT increases lesion visibility in patients with metastatic breast cancer

BACKGROUND

Correct classification of estrogen receptor (ER) status is essential for prognosis and treatment planning in patients with breast cancer (BC). Therefore, it is recommended to sample tumor tissue from an accessible metastasis. However, ER expression can show intra- and intertumoral heterogeneity. 16α-[18F]fluoroestradiol ([18F]FES) Positron Emission Tomography/Computed Tomography (PET/CT) allows noninvasive whole-body (WB) identification of ER distribution and is usually performed as a single static image 60 min after radiotracer injection. Using dynamic whole-body (D-WB) PET imaging, we examine [18F]FES kinetics and explore whether Patlak parametric images ( K i ) are quantitative and improve lesion visibility.

RESULTS

This prospective study included eight patients with metastatic ER-positive BC scanned using a D-WB PET acquisition protocol. The kinetics of [18F]FES were best characterized by the irreversible two-tissue compartment model in tumor lesions and in the majority of organ tissues. K i values from Patlak parametric images correlated with K i values from the full kinetic analysis, r2 = 0.77, and with the semiquantitative mean standardized uptake value (SUVmean), r2 = 0.91. Furthermore, parametric K i images had the highest target-to-background ratio (TBR) in 162/164 metastatic lesions and the highest contrast-to-noise ratio (CNR) in 99/164 lesions compared to conventional SUV images. TBR was 2.45 (95% confidence interval (CI): 2.25-2.68) and CNR 1.17 (95% CI: 1.08-1.26) times higher in K i images compared to SUV images. These quantitative differences were seen as reduced background activity in the K i images.

CONCLUSION

[18F]FES uptake is best described by an irreversible two-tissue compartment model. D-WB [18F]FES PET/CT scans can be used for direct reconstruction of parametric K i images, with superior lesion visibility and K i values comparable to K i values found from full kinetic analyses. This may aid correct ER classification and treatment decisions. Trial registration ClinicalTrials.gov: NCT04150731, https://clinicaltrials.gov/study/NCT04150731.

Imaging Molecular Targets and Metabolic Pathways in Breast Cancer for Improved Clinical Management: Current Practice and Future Perspectives

Breast cancer is the most frequently diagnosed cancer and leading cause of cancer-related deaths worldwide. Timely decision-making that enables implementation of the most appropriate therapy or therapies is essential for achieving the best clinical outcomes in breast cancer. While clinicopathologic characteristics and immunohistochemistry have traditionally been used in decision-making, these clinical and laboratory parameters may be difficult to ascertain or be equivocal due to tumor heterogeneity. Tumor heterogeneity is described as a phenomenon characterized by spatial or temporal phenotypic variations in tumor characteristics. Spatial variations occur within tumor lesions or between lesions at a single time point while temporal variations are seen as tumor lesions evolve with time. Due to limitations associated with immunohistochemistry (which requires invasive biopsies), whole-body molecular imaging tools such as standard-of-care [18F]FDG and [18F]FES PET/CT are indispensable in addressing this conundrum. Despite their proven utility, these standard-of-care imaging methods are often unable to image a myriad of other molecular pathways associated with breast cancer. This has stimulated interest in the development of novel radiopharmaceuticals targeting other molecular pathways and processes. In this review, we discuss validated and potential roles of these standard-of-care and novel molecular approaches. These approaches' relationships with patient clinicopathologic and immunohistochemical characteristics as well as their influence on patient management will be discussed in greater detail. This paper will also introduce and discuss the potential utility of novel PARP inhibitor-based radiopharmaceuticals as non-invasive biomarkers of PARP expression/upregulation.

Does F-18 FDG-PET/CT Have an Additional Impact on Axillary Approach in Early-Stage Breast Cancer?

Objective

Breast cancer (BC) is a significant health concern and one of the most diagnosed cancers in women, both in Turkey and globally. Despite advances in the management of BC, axillary lymph node involvement remains a significant consideration for treatment planning, local recurrence, and prognosis. We aimed to evaluate the contribution of F-18 fluorodeoxyglucose-positron emission tomography/computed tomography (F-18 FDG-PET/CT) in detecting axillary lymph node metastasis compared to ultrasound (US).

Materials and Methods

Eighty patients who were diagnosed with stage I and II BC and underwent US and F-18 FDG-PET/CT scans before surgery were enrolled in this study. Those who did not undergo F-18 FDG-PET/CT imaging, patients with distant metastases at the time of diagnosis and patients with micrometastases in the axilla were excluded from the analysis. Imaging results of the status of axillary lymph nodes were verified with the final pathology report of axillary lymph nodes.

Results

The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of F-18 FDG-PET/CT for the detection of ipsilateral axillary lymph node metastases were 75%, 77.27%, 72.97%, 79.07%, and 76.25%. The corresponding values for US were 72.22%, 81.82%, 76.47%, 78.26%, and 77.50%, respectively. When US finding is negative or suspicious in axillary lymph node evaluation, the accuracy of F-18 FDG-PET/CT for the detection of ipsilateral axillary lymph node metastases were 65.38%, 83.33%, 70.83%, and 79.55%, respectively.

Conclusion

This study found that F-18 FDG-PET/CT does not provide an additional advantage over US in assessing the axilla in early-stage disease.

Head-to-head comparison of 18F-FDG and 18F-FES PET/CT for initial staging of ER-positive breast cancer patients

PURPOSE

To compare the diagnostic performance of 18F-fluorodeoxyglucose (18F-FDG) and 18F-fluoroestradiol (18F-FES) positron emission tomography/computed tomography (PET/CT) for initial staging of estrogen receptor (ER) positive breast cancer.

METHODS

Twenty-eight patients with ER-positive breast cancer underwent 18F-FDG and 18F-FES PET/CT for initial staging. Diagnostic performance and concordance rates were analyzed for both radiotracers. Semiquantitative parameters of maximum standardized uptake value (SUVmax) and tumor-to-normal ratio (T/N ratio) were compared using Wilcoxon signed-rank test. Factors potentially affecting the degree of radiotracer uptake were analyzed by multi-level linear regression analysis.

RESULTS

The overall diagnostic performance of 18F-FES was comparable to 18F-FDG, except for higher specificity and NPV, with sensitivity, specificity, PPV, NPV, and accuracy of 87.56%, 100%, 100%, 35.14%, and 88.35%, respectively, for 18F-FES and 83.94%, 30.77%, 94.74%, 11.43%, and 95.37%, respectively, for 18F-FDG. Diagnostic performance of strong ER expression was better in 18F-FES but worse for 18F-FDG. There was a correlation of mucinous cell type and Allred score 7-8 with 18F-FES uptake, with correlation coefficients of 26.65 (19.28, 34.02), 5.90 (- 0.005, 11.81), and p-value of < 0.001, 0.05, respectively. Meanwhile, luminal B and Ki-67 were related to 18F-FDG uptake, with correlation coefficients of 2.76 (1.10, 0.20), 0.11 (0.01, 0.2), and p-value of 0.018, 0.025, respectively.

CONCLUSION

Diagnostic performance of 18F-FES is comparable to 18F-FDG, but better for strongly ER-positive breast cancer. Combination of 18F-FES and 18F-FDG would potentially overcome the limitations of each tracer with more accurate staging.

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

INTRODUCTION

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

CASE AND OUTCOMES

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

DISCUSSION

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

CONCLUSION

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

Evaluation of Treatment Response in Patients with Breast Cancer

Breast cancer (BC) remains one of the leading causes of death among women. The management and outcome in BC are strongly influenced by a multidisciplinary approach, which includes available treatment options and different imaging modalities for accurate response assessment. Among breast imaging modalities, MR imaging is the modality of choice in evaluating response to neoadjuvant therapy, whereas F-18 Fluorodeoxyglucose positron emission tomography, conventional computed tomography (CT), and bone scan play a vital role in assessing response to therapy in metastatic BC. There is an unmet need for a standardized patient-centric approach to use different imaging methods for response assessment.

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.

[18F]FES PET Resolves the Diagnostic Dilemma of COVID-19-Vaccine-Associated Hypermetabolic Lymphadenopathy in ER-Positive Breast Cancer

Coronavirus disease (COVID-19) vaccination is known to cause a diagnostic dilemma due to false-positive findings on [¹⁸F]FDG PET in vaccine-associated hypermetabolic lymphadenopathy. We present two case reports of women with estrogen-receptor (ER)-positive cancer of the breast who were vaccinated for COVID-19 in the deltoid muscle. [¹⁸F]FDG positron emission tomography (PET) demonstrated primary breast cancer and multiple axillary lymph nodes with increased [¹⁸F]FDG uptake, diagnosed as vaccine-associated [¹⁸F]FDG-avid lymph nodes. Subsequent [¹⁸F]FES PET revealed single axillary lymph node metastasis in the vaccine-associated [¹⁸F]FDG-avid lymph nodes. To the best of our knowledge, this is the first study showing the usefulness of [¹⁸F]FES PET in diagnosing axillary lymph node metastasis in COVID-19-vaccinated patients harboring ER-positive breast cancer. Thus, [¹⁸F]FES PET has potential applications in the detection of true-positive metastatic lymph nodes in patients with ER-positive breast cancer regardless of the ipsilateral or contralateral side, who have received COVID-19 vaccination.

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 Imaging Assessment of Hormonally Sensitive Breast Cancer: An Appraisal of 2-[18F]-Fluoro-2-Deoxy-Glucose and Newer Non-2-[18F]-Fluoro-2-Deoxy-Glucose PET Tracers

Hormone-sensitive breast cancer, which demonstrates hormone receptor positivity, accounts for approximately 75% of newly diagnosed breast cancer. 2-[18F]-Fluoro-2-deoxy-glucose is the nonspecific radiotracer of glucose metabolism as opposed to specific receptor based tracers like 16α-[18F]-fluoro-17β-estradiol and [18F]-fluoro-furanyl-norprogesterone, which provide essential information about receptor status in the management of hormonally active malignancies. The complementary information provided by (a) 2-[18F]-fluoro-2-deoxy-glucose imaging for staging and prognostication along with (b) analyzing the hormonal receptor status with receptor-based PET imaging in breast cancer can optimize tumor characterization and influence patient management.

Association between tumor 18F-fluorodeoxyglucose metabolism and survival in women with estrogen receptor-positive, HER2-negative breast cancer

We examined whether ¹⁸F-fluorodeoxyglucose metabolism is associated with distant relapse-free survival (DRFS) and overall survival (OS) in women with estrogen receptor (ER)-positive, HER2-negative breast cancer. This was a cohort study examining the risk factors for survival that had occurred at the start of the study. A cohort from Asan Medical Center, Korea, recruited between November 2007 and December 2014, was included. Patients received anthracycline-based neoadjuvant chemotherapy. The maximum standardized uptake value (SUV) of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) was measured. The analysis included 466 women. The median (interquartile range) follow-up period without distant metastasis or death was 6.2 (5.3-7.6) years. Multivariable analysis of hazard ratio (95% confidence interval [CI]) showed that the middle and high tertiles of SUV were prognostic for DRFS (2.93, 95% CI 1.62-5.30; P < 0.001) and OS (4.87, 95% CI 1.94-12.26; P < 0.001). The 8-year DRFS rates were 90.7% (95% CI 85.5-96.1%) for those in the low tertile of maximum SUV vs. 73.7% (95% CI 68.0-79.8%) for those in the middle and high tertiles of maximum SUV. ¹⁸F-fluorodeoxyglucose PET/CT may assess the risk of distant metastasis and death in ER-positive, HER2-negative patients.

18F-FES PET/CT Improves the Detection of Intraorbital Metastases in Estrogen-Receptor-Positive Breast Cancer: Two Representative Cases and Review of the Literature

Orbital metastases are a rare but life-altering complication in cancer. Most commonly seen in breast cancer, metastases to the optic nerves or extraocular muscles can have a devastating impact on visual acuity and quality of life. Hormone receptor status plays a central role in metastatic breast cancer treatment, with endocrine therapy often representing first-line therapy in hormone-receptor-positive cancers. Staging and treatment response evaluation with positron emission tomography (PET) computed tomography (CT) imaging with 18F-fluorodeoxyglucose (18F-FDG) is limited by high physiologic uptake in the intracranial and intraorbital compartments. Thus, traditional staging scans with 18F-FDG PET/CT may under-detect intraorbital and intracranial metastatic disease and inaccurately evaluate active metastatic disease burden. In comparison, 18F-fluoroestradiol (18F-FES) is a novel estrogen-receptor-specific PET radiotracer, which more accurately assesses the intracranial and intraorbital compartments in patients with estrogen-receptor-positive (ER+) cancers than 18F-FDG, due to lack of physiologic background activity in these regions. We present two cases of breast cancer patients with orbital metastases confirmed on MR imaging who underwent PET/CT imaging with 18F-FES and 18F-FDG. Multimodality imaging with 18F-FES PET/CT offers higher detection sensitivity of orbital metastases, compared with traditional 18F-FDG PET/CT imaging, and can improve the assessment of treatment response in patients with estrogen-receptor-positive (ER+) cancers.

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.

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.