Breast CancerPhase 3POWERNCT07502820
The POWER Trial: Personalised Dose Optimisation With Adjuvant Tamoxifen Therapy in Breast cancER
A Phase 3 study testing Individual dose of tamoxifen and Standard adjuvant therapy of tamoxifen in people with Breast Cancer and Adjuvant Drug Therapy, run by Karolinska Institutet at 4 sites in Sweden.
Trial summary
In Sweden, approximately 7000 women are diagnosed with hormone-sensitive breast cancer annually. According to international and national guidelines, most of these women are recommended anti-hormonal therapy for five to ten years to improve prognosis. Read more about this study
- Who is it for?
- Ages 18 years and older, women only
- Conditions the study is for
- Breast Cancer, Adjuvant Drug Therapy
- What is being tested?
- Individual dose of tamoxifen and Standard adjuvant therapy of tamoxifen
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 1,100 participants
- Where
- 4 sitesSweden
- Study dates
- 14 Apr 2026to Aug 2036
- Phase
- Phase 3
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- Women only
- No healthy volunteers
- Adult, Older adult
Who may be able to join
- Patients with primary breast cancer, recommended for adjuvant tamoxifen treatment with or without concomitant goserelin
- Premenopausal or perimenopausal, defined according to SOC for therapy decision
- Eastern Cooperative Oncology Group (ECOG) WHO Performance Scale 0 - 2
- Participants must use non-hormonal contraception during the trial.
Who cannot join
- Previous use of tamoxifen, endoxifen, or aromatase inhibitors.
- Previous medical history of:
- Deep venous thrombosis or pulmonary embolism; bleeding disorder or coagulopathy; macular disorders, retinal disorders, severe cataract or glaucoma.
- Current use of warfarin.
- Not willing to abstain from strong and moderate CYP2D6 inhibitors or CYP3A4 inducers during the tamoxifen treatment
- Current pregnancy, breastfeeding, or already at start of tamoxifen planning to become pregnant within the next two years
- Use of systemic menopausal hormonal therapy (MHT).
- Prior invasive malignancy during the last five years. Prior or current in situ cancers are allowed.
Trial locations and contacts
4 sites in 1 country. Contact the study team or a site near you to ask about taking part.
Sweden4 sites, 4 recruiting
- Not yet recruiting
S:a Älvsborgs Sjukhus
Borås, 501 82
Rebecka Landin, MD PhD
- Recruiting
Skaraborgs Sjukhus
Skövde, 549 49
Chaido Chamalidou, MD PhD
- Not yet recruiting
Capio S:t Görans Sjukhus
Stockholm, 112 81
Jenny Bergqvist, MD PhD
- Recruiting
Södersjukhuset, Onkologiska kliniken
Stockholm, 118 61
Linda Thorén, MD PhD
About this study
Official title: The POWER Trial: A Randomised, Two-armed Open Label Phase 3 Clinical Trial on Personalised Dose Optimisation With Adjuvant Tamoxifen Therapy After Breast Cancer to Investigate the Impact on Discontinuation and Efficacy Compared to Standard of Care
In Sweden, approximately 7000 women are diagnosed with hormone-sensitive breast cancer annually. According to international and national guidelines, most of these women are recommended anti-hormonal therapy for five to ten years to improve prognosis. Tamoxifen, one of the most widely used anti-hormonal agents globally, reduces the risk of recurrence by 40% and breast cancer mortality by 30%.
Tamoxifen is a pro-drug that undergoes hepatic metabolism to form endoxifen and other active metabolites. Variability in metabolic capacity affects therapeutic efficacy: poor metabolisers produce insufficient endoxifen and other active metabolites, risking therapeutic failure, while ultrarapid metabolisers generate excessive amounts, leading to intolerable adverse effects. Today, 30-50% of patients discontinue treatment prematurely due to severe side effects, resulting in suboptimal outcomes.
Currently, tamoxifen is uniformly prescribed at a daily dose of 20 mg, and so far, no clinical trials have tested whether individualised dosing could enhance adherence and improve survival outcomes. The primary objective is to evaluate whether individualised tamoxifen dosing reduces discontinuation rates and enhances patient outcomes in breast cancer treatment.
- Conditions
- Breast Cancer, Adjuvant Drug Therapy
- Being tested
- Individual dose of tamoxifen, Standard adjuvant therapy of tamoxifen
- Keywords
- Early-stage breast cancer, Adjuvant, Endocrine therapy, Tamoxifen, Therapeutic drug monitoring TDM, Precision medicine
- Medical subject headings
- Breast Neoplasms
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Individual dose of tamoxifenDrug
Each subject starts their treatment with the standard dose 20 mg tamoxifen daily by oral intake. During visits 2 (3 months), 3 (six months) and 4 (twelve months), the investigator will either let the patient remain on 20 mg tamoxifen or individualise the dose.
The investigator may change the daily tamoxifen from 20 mg per day to:
a halved dose to 10 mg, or a doubled dose to 40 mg.
The recommendation for oral intake of tablet(s) tamoxifen for a daily dose of 10, 20 or 40 mg is accordingly:
for 10 mg: one tablet (20 mg) every two days for 20 mg: one tablet (20 mg) every day for 40 mg: two tablets (20 mg) every day.
Standard adjuvant therapy of tamoxifenDrug
The global standard dose for everyone is 20 mg orally once per day. Each subject undergoes treatment with the standard dose 20 mg daily by oral intake of one tablet, with no possibility of dose adjustment during the trial.
| Study group | Role | What they receive |
|---|---|---|
| Individualised care with tamoxifen dose adjustments. | Experimental | Patients randomised to individualised care will have their dose adjusted according to an algorithm based on patient reported side effects and the concentration of (z)-endoxifen in blood. Receives: Drug: Individual dose of tamoxifen |
| Standard-of-care with the standard tamoxifen dose of 20 mg orally once per day. | Active comparator | In the control arm, each subject undergoes treatment with the standard dose 20 mg tamoxifen daily by oral intake of one tablet, with no possibilty of dose adjustment during the trial. Receives: Drug: Standard adjuvant therapy of tamoxifen |
What is being measured
The primary outcome is the main question the study is designed to answer.
Discontinuation of tamoxifen.
The primary outcome is discontinuation of tamoxifen. This will be declared when any of the following four criteria are satisfied:
- Agreement between patient and doctor that the patient will discontinue tamoxifen.
- Patient notifies doctor that she has discontinued tamoxifen.
- Patient-reported tamoxifen tablet intake of zero tablets for 13 consecutive weeks.
- Patient refuses dose of tamoxifen as recommended per protocol by their clinician.
Measured: From enrollment to end of treatment at 60 months.
Secondary outcomes (11)
Patient reported outcomes.
At baseline and two weeks before the doctor's appointment at 3, 6 and 12 months after start of tamoxifen therapy all patients will answer the POWER symptom burden questionnaire. Patients will be answering questionnaires yearly year 2-5 from start of tamoxifen. The purpose is evaluate treatment-related side effects (e.g., tamoxifen).
The symptom burden questionnaire includes the BCPT Eight Symptom Scale (BESS) (derived from the 42-item Breast Cancer Prevention Trial checklist), which is a 30-item, 5-point Likert-type, self-report tool measuring symptom distress in breast cancer patients over the past four weeks. It covers eight specific domains (hot flashes, nausea, bladder/vaginal problems, pain, cognitive, weight, arm problems). Higher scores indicate higher symptom distress, where patients rate how "bothered" they were on a scale of 0 (Not at all) to 4 (Extremely).
Measured: From enrollment to end of treatment at 60 months.
Quality of life questionnaire
At baseline and two weeks before the doctor's appointment at 3, 6 and 12 months after start of tamoxifen therapy all patients will answer the quality-of-life questionnaire designed for this study. A prespecified set of answers from the questionnaire will be available for the doctor and patient to discuss at the appointment. Patient will be answering the same questionnaire yearly year 2-5 in the study. The results from the questionnaires will not be discussed with the patient but analysed at the end of the study.
Measured: From enrollment to end of treatment at 60 months.
Concentration of circulation plasma metabolites
Tamoxifen and the metabolites 4-OH-tamoxifen, N-DM-tamoxifen, and endoxifen will be analysed in plasma at each blood collection time point.
For patients in the intervention arm, the endoxifen concentration will be accessible in the patient eCRF and discussed at the doctor's visit for decision on the appropriate dose. For patients in the control arm, neither the patient nor the doctor will have access to the endoxifen concentrations during the trial. Endoxifen concentrations in the control arm will remain pseudonymised and stored on servers without access for investigators or relevant study personnel until end-of-trial.
Measured: From 3 months after treatment start to end of treatment at 60 months
Invasive disease-free survival (iDSF)
iDSF measures the time from randomized treatment or surgery until the first occurrence of an invasive cancer recurrence, a new primary invasive cancer, or death from any cause. Study site will report first recurrence, local or distant during the patients 5 years in the study. For long-term follow-up the information about first recurrence or death will be collected from the National Cancer Registry.
Measured: From enrollment to end of treatment at 60 months.
Distant relapse-free survival (DRFS)
DRFS measures the time from primary cancer treatment until the first recurrence at a distant site (metastasis) or death from the cancer, excluding local-regional recurrences. Site will report first recurrence during the patients 5 years in the study. For long-term follow-up the information about first recurrence or death will be collected from the National Cancer Registry.
Measured: From enrollment to end of treatment at 60 months.
Breast cancer specific survival (BCSS)
BCSS is the percentage of people with a specific type and stage of breast cancer who are alive at a certain time (often 5 or 10 years) following diagnosis, accounting only for deaths caused by that cancer. Unlike overall survival, BCSS excludes deaths from other causes. The site will report during the patients 5 years in the study. For long-term follow-up, the information about death will be collected from the National Cancer Registry.
Measured: From enrollment to end of treatment at 60 months.
Overall survival (OS)
The study site will report death during the first 5 years in the study. For long-term follow-up the information about death will be collected from the National Cause-of-Death registry.
Measured: From enrollment to end of treatment at 60 months.
Mammographic breast density
Assess change in mammographic density including time-and dose-dependent trends in density change. The mammograms will be collected for a centralised assessment of density and density change. An automated, digital software, e.g. the Stratus software, will be used to measure mammographic features such as density, macrocalcifications and masses.
Measured: From enrollment to end of treatment at 60 months.
Cost effectiveness Analysis (CEA)
CEA will be used to compare relative costs and effects of the intervention, expressed as Quality-Adjusted Life Years (QUALYs) gained. Cost effectiveness and values of the intervention i.e. individualised adjuvant tamoxifen will be evaluated using the POWER trial questionnaires, medical records, National Register information, number and extents of health care contacts, and concomitant medications, collected through the trial.
Measured: From enrollment to end of treatment at 60 months.
Cost-Benefit Analysis (CBA)
CBA will be used to investigate any monetary value of individualised tamoxifen, measured by impacts on all direct and indirect costs. Values of the intervention i.e. individualised adjuvant tamoxifen will be evaluated using the POWER trial questionnaires, medical records, National Register information, number and extent of health care contacts. and concomitant medications, collected through the trial.
Measured: From enrollment to end of treatment at 60 months.
Incremental cost-effectiveness ratio (ICER)
ICER will be calculated by dividing the incremental cost of the intervention i.e. individualised adjuvant tamoxifen by its incremental health benefit.
Cost effectiveness and values of the intervention will be evaluated using the POWER trial questionnaires, medical records, National Register information, number and extents of health care contacts, and concomitant medications, collected through the trial.
Measured: From enrollment to end of treatment at 60 months.
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted31 Mar 2026
- Study start14 Apr 2026
- Primary completionAug 2036 (estimated)
- Study completionAug 2036 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Breast CancerStudies of the same condition, open and under way.
- More trials run by Karolinska InstitutetThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 3
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Enrolment
- 1,100 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Karolinska Institutet
- Sponsor type
- University, hospital or other
- Collaborators
- Swedish Cancer Society, Region Stockholm, The Swedish Breast Cancer Association, The Sjöberg Foundation, The Cancer Research Foundations of Radiumhemmet
- Responsible party
- Principal investigator, Marike Gabrielson, Karolinska Institutet
- Investigators
- Marike Gabrielson, PhD, Principal investigator, Karolinska InstitutetJenny Bergkvist, MD, PhD, Study chair, Karolinska Institutet
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07502820
- Sponsor's protocol ID
- 2025-522240-40-00
- Other IDs
- 2025
- Acronym
- POWER
- Status last verified
- Mar 2026
- First submitted
- 18 Mar 2026
- Last updated
- 12 Aug 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No
Study at a glance
From the registry record, last updated by the sponsor on 12 Aug 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- The POWER Trial: A Randomised, Two-armed Open Label Phase 3 Clinical Trial on Personalised Dose Optimisation With Adjuvant Tamoxifen Therapy After Breast Cancer to Investigate the Impact on Discontinuation and Efficacy Compared to Standard of Care
- ClinicalTrials.gov ID
- NCT07502820
- Acronym / sponsor ID
- POWER / 2025-522240-40-00
- Conditions
- Breast Cancer, Adjuvant Drug Therapy
- Keywords
- Early-stage breast cancer, Adjuvant, Endocrine therapy, Tamoxifen, Therapeutic drug monitoring TDM, Precision medicine
- Phase
- Phase 3
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 1,100 participants (estimated)
- Lead sponsor
- Karolinska InstitutetUniversity, hospital or other
- Collaborators
- Swedish Cancer Society, Region Stockholm, The Swedish Breast Cancer Association, The Sjöberg Foundation, The Cancer Research Foundations of Radiumhemmet
- Study start
- 14 Apr 2026 (actual)
- Primary completion
- Aug 2036 (estimated)
- Study completion
- Aug 2036 (estimated)
- First posted
- 31 Mar 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
In Sweden, approximately 7000 women are diagnosed with hormone-sensitive breast cancer annually. According to international and national guidelines, most of these women are recommended anti-hormonal therapy for five to ten years to improve prognosis. Tamoxifen, one of the most widely used anti-hormonal agents globally, reduces the risk of recurrence by 40% and breast cancer mortality by 30%.
Tamoxifen is a pro-drug that undergoes hepatic metabolism to form endoxifen and other active metabolites. Variability in metabolic capacity affects therapeutic efficacy: poor metabolisers produce insufficient endoxifen and other active metabolites, risking therapeutic failure, while ultrarapid metabolisers generate excessive amounts, leading to intolerable adverse effects. Today, 30-50% of patients discontinue treatment prematurely due to severe side effects, resulting in suboptimal outcomes.
Currently, tamoxifen is uniformly prescribed at a daily dose of 20 mg, and so far, no clinical trials have tested whether individualised dosing could enhance adherence and improve survival outcomes. The primary objective is to evaluate whether individualised tamoxifen dosing reduces discontinuation rates and enhances patient outcomes in breast cancer treatment.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| Individualised care with tamoxifen dose adjustments. | Experimental | Drug: Individual dose of tamoxifenPatients randomised to individualised care will have their dose adjusted according to an algorithm based on patient reported side effects and the concentration of (z)-endoxifen in blood. |
| Standard-of-care with the standard tamoxifen dose of 20 mg orally once per day. | Active comparator | Drug: Standard adjuvant therapy of tamoxifenIn the control arm, each subject undergoes treatment with the standard dose 20 mg tamoxifen daily by oral intake of one tablet, with no possibilty of dose adjustment during the trial. |
Who may qualify
- Ages
- 18 years and older
- Sex
- Female only
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (4 listed)
- Patients with primary breast cancer, recommended for adjuvant tamoxifen treatment with or without concomitant goserelin
- Premenopausal or perimenopausal, defined according to SOC for therapy decision
- Eastern Cooperative Oncology Group (ECOG) WHO Performance Scale 0 - 2
- Participants must use non-hormonal contraception during the trial.
Key exclusion criteria (8 listed)
- Previous use of tamoxifen, endoxifen, or aromatase inhibitors.
- Previous medical history of:
- Deep venous thrombosis or pulmonary embolism; bleeding disorder or coagulopathy; macular disorders, retinal disorders, severe cataract or glaucoma.
- Current use of warfarin.
- Not willing to abstain from strong and moderate CYP2D6 inhibitors or CYP3A4 inducers during the tamoxifen treatment
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Individual dose of tamoxifenEach subject starts their treatment with the standard dose 20 mg tamoxifen daily by oral intake. During visits 2 (3 months), 3 (six months) and 4 (twelve months), the investigator will either let the patient remain on 20 mg tamoxifen or individualise the dose. The investigator may change the daily tamoxifen from 20 mg per day to: a halved dose to 10 mg, or a doubled dose to 40 mg. The recommendation for oral intake of tablet(s) tamoxifen for a daily dose of 10, 20 or 40 mg is accordingly: for 10 mg: one tablet (20 mg) every two days for 20 mg: one tablet (20 mg) every day for 40 mg: two tablets (20 mg) every day. | Drug | Individualised care with tamoxifen dose adjustments. |
| Standard adjuvant therapy of tamoxifenThe global standard dose for everyone is 20 mg orally once per day. Each subject undergoes treatment with the standard dose 20 mg daily by oral intake of one tablet, with no possibility of dose adjustment during the trial. | Drug | Standard-of-care with the standard tamoxifen dose of 20 mg orally once per day. |
Primary outcome
Discontinuation of tamoxifen.
Time frame: From enrollment to end of treatment at 60 months.
The primary outcome is discontinuation of tamoxifen. This will be declared when any of the following four criteria are satisfied: * Agreement between patient and doctor that the patient will discontinue tamoxifen. * Patient notifies doctor that she has discontinued tamoxifen. * Patient-reported tamoxifen tablet intake of zero tablets for 13 consecutive weeks. * Patient refuses dose of tamoxifen as recommended per protocol by their clinician.
11 secondary outcomes
Patient reported outcomes.
Time frame: From enrollment to end of treatment at 60 months.
Quality of life questionnaire
Time frame: From enrollment to end of treatment at 60 months.
Concentration of circulation plasma metabolites
Time frame: From 3 months after treatment start to end of treatment at 60 months
Invasive disease-free survival (iDSF)
Time frame: From enrollment to end of treatment at 60 months.
Distant relapse-free survival (DRFS)
Time frame: From enrollment to end of treatment at 60 months.
Breast cancer specific survival (BCSS)
Time frame: From enrollment to end of treatment at 60 months.
Overall survival (OS)
Time frame: From enrollment to end of treatment at 60 months.
Mammographic breast density
Time frame: From enrollment to end of treatment at 60 months.
Cost effectiveness Analysis (CEA)
Time frame: From enrollment to end of treatment at 60 months.
Cost-Benefit Analysis (CBA)
Time frame: From enrollment to end of treatment at 60 months.
Incremental cost-effectiveness ratio (ICER)
Time frame: From enrollment to end of treatment at 60 months.
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 12 Aug 2026.
- Individual participant dataSharing planned: No
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Marike Gabrielson, PhD principal investigator
Karolinska Institutet
Jenny Bergkvist, MD, PhD study chair
Karolinska Institutet
4 sites in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 3 study testing Individual dose of tamoxifen and Standard adjuvant therapy of tamoxifen in people with Breast Cancer and Adjuvant Drug Therapy, run by Karolinska Institutet at 4 sites in Sweden.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 8 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 12 Aug 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 4 sites in Sweden. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Helena Aaröe, RN (+46852482267, powerstudien-meb@ki.se), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Discontinuation of tamoxifen. (time frame: From enrollment to end of treatment at 60 months.). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 12 Aug 2026.