<p>Adjuvant systemic therapy remains the cornerstone of treatment for patients with early-stage HR+/HER2- breast cancer. A range of therapies is now available, allowing for treatment individualization. Researchers at the recent <strong>2025 ASCO Annual Meeting</strong> presented studies emphasizing the use of adjuvant systemic therapy in patients with early-stage HR+/HER2- breast cancer.</p> <p><br></p> <p><em>Following these presentations, featured expert Harold J. Burstein, MD, PhD, was interviewed by </em>Conference Reporter<em> Associate Editor-in-Chief Christopher Ontiveros, PhD. Clinical perspectives from Dr Burstein on these findings are presented here.</em></p>

The most common type of breast cancer around the world is ER+/HER2- breast cancer. For women with early-stage ER+ breast cancer, the standard of care is to give adjuvant antiestrogen medicines (ie, tamoxifen for pre- or postmenopausal patients or an aromatase inhibitor for postmenopausal patients). These options are available worldwide and reduce the risk of recurrence and mortality.

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For younger women who are premenopausal, we discuss ovarian function suppression (OFS) with medication or the surgical removal of the ovaries as a way to reduce the risk of cancer recurrence. Results from 2 really important studies that looked at adjuvant OFS were presented at ASCO 2025.

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The first of those abstracts was an analysis of the SOFT and TEXT trials presented by Prudence A. Francis, MD, FRACP (abstract 505). TEXT was evaluating adjuvant exemestane and OFS vs tamoxifen and OFS, while SOFT was evaluating adjuvant exemestane and OFS vs tamoxifen and OFS vs tamoxifen alone, in premenopausal women with early-stage HR+ breast cancer. With 15 years of follow-up, researchers found that adjuvant OFS lowers the risk of cancer recurrence for premenopausal women with ER+ breast cancers, particularly those with higher-risk cancers. It independently contributes to marginally better outcomes for these younger women than tamoxifen alone. The related ASTRRA trial, which was presented at ASCO 2025 by Jai Min Ryu, MD, PhD, also showed a benefit by adding OFS to tamoxifen at the 10-year analysis (abstract 506). I think that one of the real highlights of the ASCO meeting was figuring out who needs what treatment for ER+ breast cancer.

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Targeted therapy is a potential adjuvant treatment option, usually for patients with higher-risk stage II or III breast cancer. The CDK4/6 inhibitors abemaciclib and ribociclib help reduce the recurrence rate for higher-risk ER+ breast cancers. NATALEE is one of the pivotal trials that evaluated adding ribociclib to adjuvant therapy for stage II or III ER+ breast cancers. That study was positive, and the drug has been US Food and Drug Administration (FDA) approved for use in the adjuvant setting.

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The results of a subset analysis of NATALEE by menopausal status and age were presented at ASCO 2025 by Kevin Kalinsky, MD, FASCO, MS (abstract 516). It is important to remember that study participants either had their ovaries taken out or were on OFS medication. The subgroup analysis found that all subgroups seemed to benefit from the addition of ribociclib.

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In a final presentation at ASCO 2025 related to CDK4/6 inhibitors, the TRADE study, led by my colleague Erica L. Mayer, MD, MPH, FASCO, evaluated abemaciclib dose escalation (abstract 517). One of the major side effects of abemaciclib is gastrointestinal symptoms such as cramping and diarrhea. In the TRADE study, patients with node-positive HR+/HER2- breast cancer began abemaciclib therapy at a low dose of 50 mg twice daily. After 2 weeks, the dose increased to 100 mg twice daily; after another 2 weeks, it went up to the full dose of 150 mg twice daily. The goal was to see whether, after 3 months of therapy, a greater percentage of women could continue abemaciclib therapy. The escalating approach seemed to enable a greater percentage of women to tolerate the full dose of abemaciclib. Dose escalation may help make abemaciclib more tolerable for more patients.