New Breast Density Treatment May Have Fewer Side Effects, Lower Cancer Risk

New research found that the drug endoxifen reduced mammographic breast density with fewer side effects. praetorianphoto/Getty Images. A study has found promising results with the breast cancer prevention drug (Z)-endoxifen. The drug reduced breast density safely and with fewer side effects than tamoxifen. It also had fewer troublesome side effects than this standard preventive treatment. Experts say that if further research confirms these findings, the endoxifen could help increase compliance and improve outcomes. Nearly half of all females ages 40 and older have dense breasts, which can impact breast cancer risk. A clinical trial published in the Journal of the National Cancer Institute on April 27 revealed promising results for a new breast cancer prevention approach targeting breast density. The protocol involves low doses of (Z)-endoxifen, a metabolite of the well-known drug tamoxifen. The study, known as the KARISMA Endoxifen trial, tested the effects of two daily doses of (Z)-endoxifen on mammographic breast density, a known marker of breast cancer risk and treatment response. Researchers examined whether (Z)-endoxifen could reduce breast density safely and with fewer side effects than tamoxifen, potentially offering a new option for breast cancer prevention. Here’s what they found. Studying the effects of endoxifen on breast density The KARISMA Endoxifen trial was a double-blind, randomized, placebo-controlled phase II study that enrolled premenopausal women ages 40 to 55. Researchers recruited 240 healthy participants from Sweden’s national breast cancer screening program between December 2021 and November 2023. To be eligible, participants needed to have regular menstrual cycles or confirm premenopausal status via blood tests, and to have a baseline mammogram showing measurable breast density. Women taking medications that could interfere with endoxifen metabolism were excluded. Participants were randomly assigned to one of three groups receiving daily