Skip to content
Clinical Trials – home

Rare diseases

Investigational molecules

Locations

Our offerNewsroom

Recruiting

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

Verified siteRegistered drugNo placebo
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

What is this trial about?

A plain-language summary of the goals, design and what participants do

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.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 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. Step 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. Step 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. Step 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 trial?

7 criteria

  • 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 trial?

12 criteria

  • 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
Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

We usually reply within a few days

Verified sites

All sites with verified contact details – recruitment status may not be available; ask directly

Trial locations

Where you can join this trial

Countries are shaded by recruitment status. Click a recruiting country to ask about joining there.

Recruiting
Not finding your country?

Not sure what to do next?

Joining a clinical trial can seem overwhelming. We guide you step by step, so you know exactly what to expect and how we support you through the process.

See the full process and FAQ

Investigated drugs

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.

What is already known about the treatment

Tamoxifen - A selective estrogen receptor modulator (SERM) administered orally as a daily tablet for breast cancer treatment and prevention. This medication works by blocking estrogen receptors in breast tissue, effectively preventing estrogen from stimulating the growth of hormone-receptor-positive breast cancer cells. Currently, tamoxifen is a well-established standard treatment in breast cancer therapy, particularly as an adjuvant treatment following primary breast cancer surgery, with a standard dose of 20 mg daily, though research is ongoing regarding personalized dosing ranging from 10 mg to 40 mg. The drug belongs to the pharmacological class of antiestrogens and has been proven effective in both pre- and post-menopausal women with hormone-receptor-positive breast cancer.

Investigated diseases

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 detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-522240-40-00Estimated enrolment1 100 patientsSponsorKarolinska Institutet

sourced from the EU Clinical Trials Register and site verification

Want to learn more about this trial or check if you can participate?

Clinical Trials Concierge

Prefer not to search? Our Concierge searches the trials for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.