An observational study in Metastatic Breast Cancer (HR+/ HER2-), sponsored by Asan Medical Center. Not yet recruiting at 1 site in South Korea. Open to participants aged 19 Years and older. Per ClinicalTrials.gov, last updated 2026-10-09.
Sponsored by Asan Medical Center · Observational
This prospective observational study aims to evaluate the prognostic value of molecular imaging biomarkers derived from baseline [18F]FES and [18F]FDG PET/CT for progression-free survival in patients with estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer receiving first-line endocrine therapy combined with a CDK4/6 inhibitor. In a subset of patients with available tumor tissue, paired tumor tissue next-generation sequencing (NGS) and circulating tumor DNA (ctDNA) analysis will also be performed to investigate their associations with imaging biomarkers, treatment response, and clinical outcomes.
Endocrine therapy combined with CDK4/6 inhibitors is a standard first-line treatment for patients with ER-positive, HER2-negative metastatic breast cancer. However, treatment response varies among patients, and both de novo and acquired endocrine resistance remain major causes of disease progression. Changes in ER expression and molecular alterations such as ESR1 mutations and alterations in the PI3K-AKT pathway have been implicated in the development of endocrine resistance.
[18F]FES PET/CT enables noninvasive whole-body assessment of ER expression in lesions, and may provide information on spatial heterogeneity of ER expression across metastatic lesions. In combination with [18F]FDG PET/CT, which reflects tumor glucose metabolism, molecular imaging may provide complementary information regarding tumor biology and treatment resistance. Imaging biomarkers reflecting inter-lesional heterogeneity in FES uptake and quantitative FDG metabolic activity may therefore be useful for predicting outcomes during endocrine therapy.
Circulating tumor DNA (ctDNA) provides a minimally invasive method for detecting tumor-derived genomic alterations, including mutations associated with endocrine resistance. Integrating ctDNA and tumor tissue genomic findings with molecular imaging may provide a more comprehensive assessment of the molecular and spatial heterogeneity of metastatic breast cancer.
This single-center, prospective observational cohort study will enroll patients with ER-positive, HER2-negative metastatic breast cancer who are scheduled to receive first-line endocrine therapy with an aromatase inhibitor combined with a CDK4/6 inhibitor. Baseline molecular imaging biomarkers will be derived from [18F]FES and [18F]FDG PET/CT. The primary objective is to evaluate the prognostic value of these imaging biomarkers for progression-free survival during first-line endocrine therapy combined with a CDK4/6 inhibitor.
In a subset of participants with adequate tumor tissue available, paired ctDNA analysis and tumor tissue next-generation sequencing will also be performed to investigate their associations with progression-free survival and molecular imaging biomarkers. Changes in [18F]FDG PET/CT findings during treatment and molecular and imaging characteristics associated with disease progression will also be explored.
12,820 studies on the registry are indexed under Breast Neoplasms; 2,920 are open to participants now.
This study's planned enrollment of 100 is below the median of 184 across 2,711 observational studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →Asan Medical Center is the lead sponsor of 578 studies on the registry; 74 are open to participants now.
Counted across the registry records on this site, refreshed daily.
Patients with ER-positive, HER2-negative metastatic breast cancer who are scheduled to initiate first-line endocrine therapy with an aromatase inhibitor in combination with a CDK4/6 inhibitor at Asan Medical Center. Potentially eligible patients will be identified from the medical oncology outpatient clinic or inpatient wards and prospectively enrolled according to the predefined eligibility criteria.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Participants with ER-positive, HER2-negative metastatic breast cancer who are scheduled to receive first-line endocrine therapy with an aromatase inhibitor in combination with a CDK4/6 inhibitor.
Diagnostic Test: [18F] FES
Participants will undergo baseline 18F-fluoroestradiol (\[18F\]FES) PET/CT before initiation of first-line endocrine therapy combined with a CDK4/6 inhibitor. \[18F\]FES (111-222 MBq) will be administered intravenously, and whole-body PET/CT imaging will be performed according to the institutional imaging protocol. \[18F\]FES PET/CT will be used to assess estrogen receptor expression and heterogeneity across metastatic lesions.
Prognostic value of baseline [18F]FES and [18F]FDG PET/CT-derived molecular imaging biomarkers for progression-free survival
Association of baseline molecular imaging biomarkers derived from \[18F\]FES and \[18F\]FDG PET/CT with progression-free survival (PFS) during first-line endocrine therapy combined with a CDK4/6 inhibitor
Time frame: From initiation of first-line endocrine therapy until the date of first documented disease progression or death from any cause, whichever occurs first, assessed up to 48 months.
Prognostic value of baseline ctDNA-based liquid biopsy biomarkers for progression-free survival
Association of baseline ctDNA-based liquid biopsy biomarkers with progression-free survival during first-line endocrine therapy combined with a CDK4/6 inhibitor
Time frame: From initiation of first-line endocrine therapy until the date of first documented disease progression or death from any cause, whichever occurs first, assessed up to 48 months.
Prognostic value of baseline tumor tissue NGS findings for progression-free survival
Association of baseline tumor tissue NGS findings with progression-free survival during first-line endocrine therapy combined with a CDK4/6 inhibitor
Time frame: From initiation of first-line endocrine therapy until the date of first documented disease progression or death from any cause, whichever occurs first, assessed up to 48 months.
Prognostic value of changes in ctDNA-based liquid biopsy biomarkers at 12 weeks for progression-free survival
Association of changes in ctDNA-based liquid biopsy biomarkers from baseline to approximately 12 weeks after treatment initiation with progression-free survival during first-line endocrine therapy combined with a CDK4/6 inhibitor.
Time frame: From 12 weeks after treatment initiation until the date of first documented disease progression or death from any cause, whichever occurs first, assessed up to 48 months after treatment initiation.
Association among baseline molecular imaging biomarkers, ctDNA-based liquid biopsy biomarkers, and tumor tissue NGS findings
Association among molecular imaging biomarkers derived from baseline \[18F\]FES and \[18F\]FDG PET/CT, baseline ctDNA-based liquid biopsy biomarkers, and tumor tissue NGS findings
Time frame: At baseline, before initiation of first-line endocrine therapy.
Prognostic value of changes in [18F]FDG PET/CT at 12 weeks for progression-free survival
Association of changes in \[18F\]FDG PET/CT findings at approximately 12 weeks after treatment initiation with progression-free survival during first-line endocrine therapy combined with a CDK4/6 inhibitor
Time frame: From 12 weeks after treatment initiation until the date of first documented disease progression or death from any cause, whichever occurs first, assessed up to 48 months after treatment initiation.
Association between changes in [18F]FDG PET/CT and changes in ctDNA-based liquid biopsy biomarkers at 12 weeks
Association between changes in \[18F\]FDG PET/CT findings and changes in ctDNA-based liquid biopsy biomarkers from baseline to approximately 12 weeks after treatment initiation.
Time frame: From baseline to approximately 12 weeks after treatment initiation.
Association among molecular imaging biomarkers, ctDNA-based liquid biopsy biomarkers, and tumor tissue NGS findings at disease progression
Association among molecular imaging biomarkers, ctDNA-based liquid biopsy biomarkers, and tumor tissue NGS findings assessed at the time of disease progression
Time frame: At the time of first documented disease progression, assessed up to 48 months after initiation of first-line endocrine therapy.
Changes in molecular imaging biomarkers, ctDNA-based liquid biopsy biomarkers, and tumor tissue NGS findings from baseline to disease progression
Changes in molecular imaging biomarkers, ctDNA-based liquid biopsy biomarkers, and tumor tissue NGS findings between baseline and the time of disease progression
Time frame: From baseline to the time of first documented disease progression, assessed up to 48 months after initiation of first-line endocrine therapy.
Prognostic value of imaging, ctDNA, and tumor tissue NGS biomarkers at disease progression for progression-free survival during second-line therapy
Association of molecular imaging biomarkers, ctDNA-based liquid biopsy biomarkers, and tumor tissue NGS findings at disease progression with progression-free survival during second-line therapy
Time frame: From initiation of second-line therapy until the date of subsequent documented disease progression or death from any cause, whichever occurs first, assessed up to 48 months after initiation of second-line therapy.
Plan to share: No
No publications or documents are linked to this record.
Start is estimated for Oct 2026; primary completion for Dec 2030, 50 months later.
Of 1,012 non-industry observational studies under Breast Neoplasms, half reached primary completion within 60 months of starting (the median), counting those still running; a quarter within 26 and three quarters within 141. This study's planned 50 months is below that.
Counting every sponsor, half of 1,165 studies reached it within 58 months; a quarter within 26 and three quarters within 125.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is not yet recruiting, as verified in Oct 2026. You cannot join it, but the record below documents what was studied.
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