A new study from Karolinska Institutet suggests that a lower-dose drug called endoxifen may offer a safer and more comfortable option for women who need treatment to reduce their risk of breast cancer.
The findings were published in the Journal of the National Cancer Institute and may help guide future approaches to prevention.
For many years, doctors have used a drug called tamoxifen to treat and prevent breast cancer. It has been in use for over 40 years and is known to reduce the risk of cancer returning after treatment. It is also sometimes given to women who have a higher risk of developing breast cancer in the first place.
Although tamoxifen is effective, it is not ideal for everyone. One of the biggest problems is its side effects. Many women who take tamoxifen experience symptoms similar to menopause, such as hot flashes and night sweats.
These side effects can be uncomfortable and difficult to manage. As a result, some women choose to stop taking the medication before completing their treatment.
Because of this, researchers have been looking for alternatives that can provide the same benefits with fewer side effects. One possible option is endoxifen. This substance is actually the active form of tamoxifen that the body produces after breaking it down. Scientists believe that taking endoxifen directly may lead to more predictable effects in the body.
In this new study, researchers tested endoxifen in tablet form to see whether it could reduce breast cancer risk markers while causing fewer side effects. The study included 240 healthy women who had not yet reached menopause.
These participants were randomly assigned to different groups. Some received a placebo, while others took either 1 milligram or 2 milligrams of endoxifen each day for six months.
To measure the effects of the treatment, the researchers focused on breast density. Breast density refers to how much dense tissue is present in the breast. Higher density is linked to a higher risk of developing breast cancer. A reduction in breast density during treatment is often seen as a positive sign that the therapy is working.
The results were encouraging. Women who took 1 milligram of endoxifen experienced an average reduction in breast density of about 19 percent. Those who took 2 milligrams saw an even larger reduction of around 26 percent.
These results are similar to what has been seen with the standard dose of tamoxifen, which typically reduces breast density by about 18.5 percent.
However, there was an important difference when it came to side effects. Women who took the higher 2 milligram dose reported more frequent hot flashes and night sweats.
In contrast, those who took the lower 1 milligram dose had a side effect profile that was similar to the placebo group. This suggests that the lower dose may offer a better balance between effectiveness and comfort.
The researchers described this study as a proof-of-concept trial. This type of study is designed to show that a treatment has the expected biological effect before larger and longer studies are carried out.
While the results are promising, the study cannot yet confirm whether endoxifen actually reduces the risk of developing breast cancer or prevents the disease from coming back.
Even so, the findings are important because they suggest that a lower dose of endoxifen may be enough to produce beneficial changes in the body while reducing unwanted side effects. This could make preventive treatment more acceptable for many women who might otherwise avoid or stop taking medication.
More research is needed to confirm these results and to understand the long-term effects of endoxifen. Future studies will need to follow patients for longer periods to see whether the reduction in breast density leads to a real decrease in cancer risk.
For now, this study offers hope for a new approach to breast cancer prevention. By finding treatments that are both effective and easier to tolerate, doctors may be able to help more women stay on therapy and reduce their risk of disease.
If you care about breast cancer, please read studies about a major cause of deadly breast cancer, and this daily vitamin is critical to cancer prevention.
For more information about cancer, please see recent studies that new cancer treatment could reawaken the immune system, and results showing vitamin D can cut cancer death risk.
Copyright © 2026 Knowridge Science Report. All rights reserved.
