(Z)-Endoxifen Reduces Mammographic Breast Density

THURSDAY, May 14, 2026 (HealthDay News) -- (Z)-endoxifen, a tamoxifen metabolite, at doses of 1 and 2 mg yields significant reductions in mammographic breast density (MBD), according to a study published online April 27 in the Journal of the National Cancer Institute.Per Hall, M.D., Ph.D., from the Karolinska Institutet in Stockholm, and colleagues measured the effect of two different doses of (Z)-endoxifen on MBD in healthy women. A total of 240 healthy premenopausal women were randomly assigned to receive placebo or 1 or 2 mg of (Z)-endoxifen daily for six months (80 in each group).The researchers found a significant relative change in MBD in both (Z)-endoxifen arms compared with placebo (−19.3 and −26.5 percent in the 1 and 2 mg arms, respectively). The numbers of participants discontinuing due to adverse events related to the investigational medicinal product were four, five, and 11 in the placebo, 1-mg, and 2-mg arms, respectively. Significantly higher scores of vasomotor symptoms were reported for participants receiving 2 mg (Z)-endoxifen versus placebo. There were no clinically significant changes in hematological safety tests or vital signs."Both 1 and 2 milligrams of endoxifen resulted in a clear reduction in breast density compared with the placebo," coauthor Mattias Hammarström, also from the Karolinska Institutet, said in a statement. "Our results suggest that a lower dose may be sufficient to affect breast density, whilst also appearing to be better tolerated."Several authors disclosed ties to Atossa Therapeutics, which funded the study.Abstract/Full Text.Sign up for our weekly HealthDay newsletter

(Z)-Endoxifen Reduces Mammographic Breast Density

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