Could tailored tamoxifen doses keep more breast cancer patients on treatment?

NCT ID NCT07502820

Disease control Sponsor: Karolinska Institutet Source: ClinicalTrials.gov ↗

First seen Jun 27, 2026 · Last updated Aug 13, 2026 · Updated 2 times

Summary

This phase 3 trial tests whether adjusting tamoxifen doses based on individual metabolism can reduce the number of breast cancer patients who stop treatment early due to side effects. About 1,100 premenopausal or perimenopausal women with hormone-sensitive breast cancer will receive either standard or personalized dosing. The goal is to improve adherence and survival outcomes.

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Study facts

What this study's own registry entry says, in plain language.

Phase

Phase 3

Large-scale testing in a bigger group. Usually the last step before a treatment can be approved.

Participants

About 1,100 people

The number the study aims to enrol. It can still change while the study runs.

Started

Apr 2026

Expected to finish

Aug 2036

An estimate. End dates often move.

Lead sponsor

Other sponsor

The registry's catch-all category, for sponsors it does not file as a company, a government agency, or a research network.

Who can take part

This study's own entry requirements. Only the study team can say for certain whether you qualify.

Ages

18 years and older

Sex

Female participants only

Healthy volunteers

Not accepted

This study is not open to healthy volunteers. The entry requirements below say who it is open to.

Show the full entry requirements

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * 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. Exclusion Criteria: * 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.

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Conditions

The condition(s) this trial relates to.

breast cancer breast neoplasm

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

Adjuvant drug therapy Breast cancer

How to take part

Only the study team decides who joins. These are the ways to reach them.

The places running it

4 sites. The list below names each one and where it is.
The official record

ClinicalTrials.gov lists the study team's own contact details, including names and phone numbers. We don't republish those.

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A doctor treating you

A doctor who knows your case can contact a study site on your behalf, and can tell you whether this study is worth pursuing at all.

Could tailored tamoxifen doses keep more breast cancer patients on treatment?

What the study statuses mean