Low Dose Tamoxifen for Mammographic Density Reduction

Inclusion Criteria: * Attending the national mammography screening program, i.e. aged 40-74 and has performed a screening mammogram maximum 3 months prior to study inclusion * Having a measurable mammographic density, i.e. ≥4.5 % density (volumetric) measured by Volpara * Informed consent must be signed before any study specific assessments have been performed Exclusion Criteria: * Pregnancy at start, during time of study medication and up to 3 months after quitting study medication * Breast feeding at start, during time of study medication and up to 3 months after quitting study medication * Any previous or current diagnosis of breast cancer (including carcinoma in situ) * Mammographic BI-RADS code 3 or above at baseline mammography, or at a diagnostic mammography during time of treatment (the first 6 months of the study) * Any previous diagnosis of cancer with the exception of non-melanoma skin cancer and in situ cancer of the cervix * Currently using oral oestrogen and progesterone based hormone replacement therapy * Current use of hormone contraceptive with hormones, e.g. hormonal contraceptive pills, or progesterone implants. Hormonal intrauterine devices are accepted. * A history of thrombo-embolic disease such as embolies, deep vein thrombosis, stroke, TIA or cardiac arrest. * Known APC (Activated protein C )- resistance, an inherited hemostatic disorder * A history of major surgery of the breast, e.g. reduction or enlargement, which might affect density measurements * Women who have an increased risk of venous thrombosis due to immobilization, e.g. using wheelchair * Known uncontrolled diabetes * Hypertension at baseline, defined as systolic pressure higher than 140 mm Hg and diastolic higher than 90 mm Hg * Use of drugs that interfere with CYP2D6 expression such as Seroxat (paroxetine), Fontex (fluoxetin) and Zyban / Voxra (bupropion) * Use of Waran (warfarin) * Non-medical approved drugs against hot-flashes including phytooestrogen * Not able to understand study information and/or informed consent