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Varying Associations ID'd Between Hormone Therapy, Young-Onset Breast Cancer

By Elana Gotkine HealthDay Reporter

Medically reviewed by Carmen Pope, BPharm. Last updated on July 10, 2025.

THURSDAY, July 10, 2025 -- Associations between hormone therapy and young-onset breast cancer (diagnosed at younger than 55 years) vary, according to a study published online in the July issue of The Lancet Oncology.

Katie M. O'Brien, Ph.D., from the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina, and colleagues examined the association between exogenous hormones and breast cancer in young women using data from 10 to 13 prospective cohorts throughout the world. Women were followed for incident breast cancer until age 55 years.

A total of 459,476 women aged 16 to 54 years were included, and of these, 8,455 (2 percent) developed young-onset breast cancer diagnosed before age 55 years. The researchers found that 15 percent of participants reported using hormone therapy, with the most common types being estrogen plus progestin hormone therapy and unopposed estrogen (6 and 5 percent, respectively). In nonusers, the cumulative incidence of young-onset breast cancer was 4.1 percent. There was no association for hormone therapy of any type with incident young-onset breast cancer, but an inverse association was seen for ever use of estrogen hormone therapy (hazard ratio, 0.86). The hazard ratio was not significant for ever use of estrogen plus progestin hormone therapy and young-onset breast cancer, but positive associations were seen for long-term use and use among women without hysterectomy or bilateral oophorectomy (hazard ratios, 1.18 and 1.15, respectively). For all breast cancer subtypes, the association between estrogen hormone therapy and young-onset breast cancer was similar, but estrogen plus progestin hormone therapy was more strongly associated with estrogen receptor-negative and triple-negative disease.

"These findings underscore the need for personalized medical advice when considering hormone therapy," senior author Dale P. Sandler, Ph.D., also from the National Institute of Environmental Health Sciences, said in a statement.

Several authors disclosed ties to the biopharmaceutical industry.

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Disclaimer: Statistical data in medical articles provide general trends and do not pertain to individuals. Individual factors can vary greatly. Always seek personalized medical advice for individual healthcare decisions.

© 2025 HealthDay. All rights reserved.

Posted July 2025

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