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

Overview

Sponsor-declared trial summary

Key facts

Sponsor

Karolinska Institutet

Participant type

Patients

Age range

18-64 years

Gender

Female

Therapeutic area

Not possible to specify

Trial duration

5 Mar 2026 → ongoing

Decision date (initial)

2025-09-02

Transition trial

No

Low-intervention

Yes

Rare-disease indication

No

Vulnerable population

No

Trial design

CTIS Part I — objectives, methods, condition coding

Main objective

Scope: Efficacy, Dose response

The primary objective of this trial is to investigate the effect of personalised dosing of tamoxifen (10 mg, 20 mg or 40 mg per day) on tamoxifen discontinuation compared to the standard regimen (20 mg per day).

Secondary objectives 8

1. To compare the effect of personalised dosing on:
2. a. Patient reported outcomes (PROM)
3. b. Quality of life
4. c. Levels of tamoxifen metabolites
5. d. Breast cancer outcomes
6. e. Overall survival (OS)
7. f. Breast density
8. g. Health economic aspects

Conditions and MedDRA coding

Breast Cancer

Eligibility criteria

Principal inclusion / exclusion criteria as submitted by sponsor

Inclusion criteria 7

1. Patients with primary breast cancer, recommended for adjuvant tamoxifen treatment with or without concomitant goserelin
2. Women aged ≥18 years
3. Premenopausal or perimenopausal, defined according to SOC för therapy decisions
4. ECOG WHO PS 0 – 2
5. Participants must use non-hormonal contraception during the trial. A pregnancy test is recommended for women of child-bearing potential who are sexually active and not using reliable contraceptive methods before inclusion
6. Able and willing to undergo blood sampling according to study protocol
7. Able and willing to give their written consent to participate in the trial

Exclusion criteria 13

1. Previous use of tamoxifen, endoxifen, or aromatase inhibitors
2. Concomitant treatment with adjuvant CDK 4/6 inhibitors or capecitabine or trastuzumab emansine.
3. Previous medical history of: Deep venous thrombosis or pulmonary embolism if not on life-long anticoagulant treatment with DOAC. A history of previous PICC-line or subcutaneous venous port associated thrombosis or superficial thrombophlebitis is allowed. Bleeding disorder or coagulopathy. Macular disorders, retinal disorder, severe cataract or glaucoma.
4. Current use of warfarin. Antiaggregants’ and direct oral anticoagulants are allowed
5. Not willing to abstain from strong and moderate CYP2D6 inhibitors or CYP3A4 inducers during the tamoxifen treatment
6. Strong and moderate inhibitors of CYP2D6 not allowed in the trial: Bupropion (Zyban), Duloxetin (Cymbalta), Fluoxetin (Fontex), Levemopromazin (Nozinan), Mirabegron (Betmiga), Paroxetin (Seroxat), Terbinafin (Lamisil) for systemic use.
7. CYP3A4 inducers not allowed in the trial (D-interactions in “Janusmedicin” janusmed.se): Efavirenz, Fenobarbital, Fenytoin, Johannesört, Karbamazepin, Primidon, Rifampicin, rifamycin.
8. Current pregnancy, breastfeeding, or already at start of tamoxifen planning to become pregnant within the next two years
9. Use of systemic menopausal hormonal therapy (MHT) and all types of systemic hormonal contraception. Local treatment is acceptable
10. Uncontrolled intercurrent physical or psychiatric illness, or social situations that would limit compliance with protocol requirements
11. Prior invasive malignancy during the last five years. Prior or current in situ cancers are allowed
12. Participation in another clinical drug trial
13. Inability to understand the study related information

Endpoints

Primary and secondary outcome measures (English text)

Primary endpoints 1

1. The primary endpoint is discontinuation of tamoxifen.

Secondary endpoints 9

1. BESS plus (2007) scale and subscales and the POWER symptom questionnaire
2. Quality of life questionnaire
3. Concentration of circulating plasma metabolites
4. Invasive disease-free survival (iDSF), Distant relapse-free survival (DRFS), Breast cancer specific survival (BCSS)
5. Overall survival (OS)
6. Mammographic breast density
7. Cost effectiveness and use of health care resources
8. Genetic polymorphisms in germline DNA
9. Biomarkers used for therapeutic drug monitoring

Investigational products

Investigational medicinal products (IMPs), comparators, placebo, auxiliary

Test 1

Sponsors and contacts

Sponsor organisations, regulatory contacts, third parties

Karolinska Institutet

Sponsor organisation

Karolinska Institutet

Address

Nobels Vag 6

City

Solna

Postcode

171 65

Country

Sweden

Scientific contact point

Organisation

Karolinska Institutet

Contact name

Marike Gabrielson

Public contact point

Organisation

Karolinska Institutet

Contact name

Marike Gabrielson

Locations

1 EU/EEA country · 9 investigational sites

By country

Investigational sites

Country notifications

Trial-start, recruitment-start, end and early-termination notifications submitted per Member State

Results and documents

Annex IV summary of results, Annex V layperson summary, and all documents registered in CTIS for this trial

Documents 5 files

Public protocol annexes, IB summaries, regulatory submissions and post-authorisation documents registered in CTIS.

Application history

1 submissions — initial application plus substantial / non-substantial modifications