Study of personalized tamoxifen dosing (10mg, 20mg, or 40mg daily) compared to standard dose (20mg) in women with breast cancer to improve treatment continuation

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What is this study about?

This clinical trial focuses on breast cancer treatment using tamoxifen, a medication used after initial breast cancer treatment to prevent the disease from returning. The study aims to compare different dosing approaches of tamoxifen to find out if personalizing the dose based on individual patient needs works better than the standard fixed dose that all patients currently receive.

The study examines whether adjusting tamoxifen doses (10 mg, 20 mg, or 40 mg daily) based on individual patient factors leads to better long-term use of the medication compared to the current standard treatment of 20 mg daily. Patients will be randomly assigned to either receive the standard fixed dose or a personalized dose. The treatment will continue for up to 5 years, during which patients will need to take tablets daily.

Throughout the study, doctors will monitor how well patients tolerate the medication and track various aspects of their health, including quality of life and any return of cancer. Blood samples will be collected to measure how the medication is working in the body. The study will also look at the density of breast tissue on mammograms and evaluate the overall effectiveness of the treatment.

1 Initial treatment assignment

You will be randomly assigned to one of two groups: either the personalized dosing group or the standard dosing group

If assigned to the standard group, you will receive 20 mg of tamoxifen daily

If assigned to the personalized group, you will receive either 10 mg, 20 mg, or 40 mg of tamoxifen daily, based on individual factors

2 Medication administration

You will take Tamoxifen Viatris tablets by mouth each day

The treatment will continue according to your assigned dosage throughout the study period

Your doctor will monitor your progress and any side effects regularly

3 Regular assessments

You will need to provide blood samples according to the study schedule

Your doctor will monitor your breast health through regular mammograms

You will complete questionnaires about your symptoms and quality of life

Regular health checkups will track your overall well-being and response to treatment

4 Long-term follow-up

The study will continue until June 2036

Your health status will be monitored throughout this period

The medical team will track any changes in your condition

Regular assessments will continue to evaluate the effectiveness of the treatment

Who Can Join the Study?

Must be diagnosed with primary breast cancer and recommended for treatment with tamoxifen (a hormone therapy medication), with or without goserelin (a hormone suppression medication)
Must be female and at least 18 years old
Must be premenopausal (still having regular menstrual periods) or perimenopausal (transitioning to menopause) according to standard medical criteria
Must have a performance status of 0-2 on the ECOG WHO scale (meaning able to care for self and be up and about more than 50% of waking hours)
Must use non-hormonal contraception during the study. Women who can become pregnant and are sexually active need to take a pregnancy test before joining if not using reliable contraception
Must be willing and able to have blood samples taken as required by the study
Must be able and willing to provide written informed consent to participate in the trial

Who Cannot Join the Study?

Male patients (study is only for female participants)
Patients under 18 or over 65 years old
Patients who are currently not taking tamoxifen (a medication used in breast cancer treatment)
Patients with known allergies or hypersensitivity to tamoxifen
Pregnant or breastfeeding women
Patients who cannot provide informed consent
Patients currently participating in other clinical trials
Patients with severe liver problems, as tamoxifen is processed by the liver
Patients with history of blood clots, as tamoxifen can increase clotting risk
Patients taking medications that could interact with tamoxifen
Patients with conditions that would prevent regular follow-up visits
Patients who have had previous adverse reactions to tamoxifen

Where you can join this trial?

Verified and Recommended Sites

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Verified Sites

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Other Sites

Site Name	City	Country
Region Oerebro Laen	Orebro	Sweden
Soedra Aelvsborg Hospital Vaestra Goetalandsregionen	Boras	Sweden
Skaraborg Hospital-Vaestra Goetalandsregionen	Skovde	Sweden
Region Skane Skanes Universitetssjukhus	Lund	Sweden
Sankt Gorans Sjukhus	Stockholm	Sweden
Malarsjukhuset Eskilstuna	Eskilstuna	Sweden
Region Joenkoepings Laen	Jönköping	Sweden
Queen Silvia Childrens Hospital – Sahlgrenska University Hospital – Vaestra Goetalandsregionen	Gothenburg	Sweden
Soedersjukhuset AB	Stockholm	Sweden

Trial status

Country	Status	Recruitment Start
Sweden	Recruiting	01.10.2025

Trial locations

Investigated drugs:

Tamoxifen

Tamoxifen is a medication used in breast cancer treatment as hormone therapy. It works by blocking the effects of estrogen in breast tissue, which can help prevent breast cancer from returning after surgery. This medication is commonly prescribed as a long-term treatment for patients who have had breast cancer, particularly in cases where the cancer was hormone-receptor positive. In this trial, researchers are studying different ways of personalizing the dose of tamoxifen to help patients better tolerate their treatment while maintaining its effectiveness.

Investigated diseases:

Breast cancer female

Breast Cancer – A disease that begins when cells in the breast start to grow out of control, typically forming a tumor that can often be seen on an x-ray or felt as a lump. It occurs when changes in genes that control cell growth cause cells to divide and multiply rapidly. The disease usually starts in the ducts that carry milk to the nipple or in the glands that make breast milk. Over time, cancer cells can invade nearby healthy breast tissue and make their way into the underarm lymph nodes. From there, they can spread to other parts of the body.

Trial ID:

2025-522240-40-00

Trial Phase:

Therapeutic confirmatory (Phase III)

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Study of personalized tamoxifen dosing (10mg, 20mg, or 40mg daily) compared to standard dose (20mg) in women with breast cancer to improve treatment continuation

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?