FES Imaging to Optimize Tamoxifen for Metastatic Breast Cancer
This study is looking at how to best use Tamoxifen, a common breast cancer drug, for people with metastatic (spread to other parts of the body) ERα+ breast cancer that has a specific change called an ESR1 gene mutation. Researchers believe that people with this mutation might need a different dose of Tamoxifen than what is usually given. The study will use a special imaging test called FES PET/CT (Positron Emission Tomography / Computed Tomography) to see how well Tamoxifen is working at different doses. This test helps measure how much the drug blocks the estrogen receptor (ERα) in the cancer cells. To join, you must have metastatic or unresectable breast cancer with at least 10% estrogen receptor expression and an ESR1 mutation. The goal is to find the best dose of Tamoxifen.
- Study design
- This is an interventional study with a planned enrollment of 12 participants. The phase of the study is not specified.
- What's involved
- Participants will receive Tamoxifen and undergo FES PET/CT imaging to compare images taken before and during treatment, for up to 6 weeks.
- Compensation
- Not stated in the trial record.
- Follow-up
- The primary endpoint, FES Blockade, is measured at up to 6 weeks to compare baseline and treatment images.
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NCT04174352
FES Imaging to Optimize Tamoxifen for Metastatic Breast Cancer
Recruiting
EARLY_PHASE1Ages 19+InterventionalTreatmentUniversity of Wisconsin, MadisonInvestigator-initiated
~12 participants
Updated 2026-07-21 on ClinicalTrials.gov
What's tested:TamoxifenFES PET/CT
At a glance
Recruiting sites
1 of 2 listed sites are recruiting right now
RecruitingSuspended, closed, or not yet open
What they're measuring
Rate of FES Blockade at each dose level to determine the Optimal Tamoxifen Dose
Measured over up to 6 weeks to compare baseline and treatment images
Conditions
Where it's being run
2 sites across 1 statesWisconsin2
Study leadership
- Kari Wisinski, MD · PRINCIPAL_INVESTIGATOR · University of Wisconsin, Madison
Who to contact
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Do you actually qualify for this trial?
Add a private profile and we'll compare every criterion below against your situation — and tell you which ones are met, uncertain, or excluding.
Eligibility criteria
Inclusion
Participants must have histologically confirmed breast cancer that is metastatic or unresectable with the following:
Estrogen receptor expression by immunohistochemistry greater than or equal to 10%
ESR1 mutation identified using a Clinical Laboratory Improvement Amendments (CLIA) certified assay via tumor biopsy tissue or circulating free DNA (cfDNA)
human epidermal growth factor receptor 2 (HER2) negative
Participants must have measurable disease as defined by RECIST 1.1 or evaluable bone disease with at least one lesion measuring 10 mm or greater in size. (Participants with bone and non-bone disease are eligible. One disease site must meet either the measurable or evaluable criteria outlined.) Participants with liver-only disease are not eligible due to the inherent hepatic uptake related to the radiopharmaceutical's hepatobiliary route of elimination.
Participants must have received at least 1 prior line of endocrine therapy in the metastatic setting or have had progression within 12 months of adjuvant endocrine therapy. Prior Tamoxifen is allowed in any setting. Prior CDK4/6 in the metastatic setting per NCCN guidelines is allowed.
Eastern Cooperative Oncology Group (ECOG) performance status 0-1 (See Appendix A)
Life expectancy of greater than 12 weeks.
Ability to take oral medications.
Informed consent: participant must be informed of the investigational nature of the study and must be able to sign a written informed consent.
Participants with central nervous system (CNS) metastases must be stable after therapy for CNS metastases (such as surgery, radiation, or stereotactic radiosurgery) for at least 1 month.
Participants must have adequate normal organ and bone marrow function as defined below:
Absolute neutrophil count \>/= 1,000/mcL
Hemoglobin \>/= 9.0 g/dL
Platelets \>/= 100,000/mcL
Total bilirubin \</= 1.5 x upper limit of normal (ULN)
AST (SGOT)/ ALT (SGPT) \</= 2.5 x ULN; \</= 5 x ULN in the setting of metastatic liver disease
Creatinine \</= 1.5 x ULN or creatinine clearance \>/= 50 mL/min
Exclusion
Prior chemotherapy, radiotherapy, targeted, immunotherapy or investigational therapy within 2 weeks or major surgery within 4 weeks of study enrollment or those who have not recovered (to grade ≤ 1 or baseline) from clinically significant adverse events due to agents administered more than 2 weeks earlier (alopecia and fatigue excluded).
Participants must not be receiving an ER blocking endocrine therapy (includes fulvestrant, tamoxifen, toremifene, raloxifene) and must be off the agents for a minimum of 60 days prior to planned FES PET/CT to allow for adequate uptake of FES.
History of allergic reactions attributed to compounds of chemical or biologic composition similar to those of tamoxifen or \[18F\]-fluoroestradiol.
Peripheral neuropathy of severity greater than grade 1.
Current optic nerve disorders, retinopathy, lattice degeneration, macular degeneration, retinal vascular disorder, or retinal tears of severity greater than grade 1.
History of cerebellar disorders, ataxia, and uncontrolled seizures unless related to transient medical condition and in investigator's opinion is not an active medical issue.
History of venous thrombosis/thromboembolic event, including pulmonary embolism and stroke.
Have a heart-rate corrected QT interval (using Fridericia's formula) (QTcF) ≥ 470msec or other factors that increase the risk of QT prolongation or arrhythmic events (e.g., heart failure, chronic hypokalemia, family history of long QT interval syndrome).
Are taking medications that are known to prolong the QT interval, unless they can be transferred to other medications ≥ 5 half-lives prior to dosing or unless the medications can be properly monitored during the study. If equivalent medication is not available, QTcF should be closely monitored.
Tamoxifen has demonstrated vaginal bleeding, birth defects and fetal loss in pregnant women. Tamoxifen use during pregnancy may have a potential long-term risk to the fetus of a Diethylstilbestrol syndrome (DES)-like syndrome. Women of childbearing potential (WOCP) must not be pregnant (confirmed by a negative urine/serum pregnancy test within 14 days of tamoxifen treatment). In addition, a medically acceptable method of birth control must be used such as an intrauterine device (IUD), use of a double barrier method (condoms, sponge, diaphragm, or vaginal ring with spermicidal jellies or cream), or total abstinence during the study participation and for 3 months after last dose of study drug. Women who are postmenopausal for at least 1 year or surgically sterile (bilateral tubal ligation, bilateral oophorectomy, or hysterectomy) are not considered to be WOCP.
Ongoing treatment with other investigational agents. Participants cannot be receiving concomitant chemotherapy, radiotherapy, experimental therapy or any other therapy not otherwise outlined by the trial for the purposes of anti-cancer treatment.
History of uterine malignancy unless participant has had hysterectomy with no evidence recurrent disease for ≥ 3 years from definitive therapy.
Concurrent malignancy except for the following:
Basal cell or squamous cell skin cancer
In situ cervical cancer
The following medications are contraindicated or must be used with caution.
Contraindicated:
CYP2D6, CYP3A4, and CYP2C9 strong inhibitors
CYP2D6, CYP3A4, and CYP2C9 strong inducers
Use with caution:
CYP2C9 sensitive substrates
CYP2D6 moderate inhibitors or inducers
CYP3A4 moderate inhibitors or inducers
Uncontrolled intercurrent clinically significant illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
What this trial measures
- Rate of FES Blockade at each dose level to determine the Optimal Tamoxifen Doseup to 6 weeks to compare baseline and treatment images
Reduction in FES uptake will be described and analyzed by Fisher's exact test. Rates or proportion of responses at each dose level will be provided in data listings. If the SUVmax for all 5 target lesions have decreased by \> 75% or all 5 lesions have SUVmax\<1.5 on the second scan, then these participants will be prospectively defined as having complete FES blockade. If the SUVmax for any of the 5 lesions has not decreased by \> 75% or if any new lesions arise with SUVmax ≥1.5, then these subjects will be defined as having incomplete FES blockade.