Age

18–any

Sex

FEMALE

Healthy volunteers

Not accepted

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.

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.

The POWER Trial: Personalised Dose Optimisation With Adjuvant Tamoxifen Therapy in Breast cancER