Why Staying on Hormone Therapy Matters When Skipping Radiation

For many people with early-stage, hormone receptor (HR)-positive breast cancer, treatment after lumpectomy has two parts: radiation to the breast and at least five years of endocrine (hormone) therapy, such as tamoxifen or an aromatase inhibitor. Some people with lower-risk disease are now offered the option of skipping radiation.

That option rests on an important assumption: that patients will keep taking their endocrine therapy for years. A study presented Sept. 27 at the American Society for Radiation Oncology (ASTRO) 2026 Annual Meeting in Boston suggests that often doesn't happen.

What the Study Looked At

Researchers at Washington University School of Medicine in St. Louis reviewed insurance claims for 17,025 people ages 23 to 64 with early-stage, HR-positive breast cancer who had a lumpectomy. Most (89%) also had radiation; 11% did not.

The researchers used pharmacy refill records to see how consistently people had their endocrine therapy on hand. The usual standard for adherence is having medication available at least 80% of the time.

What It Found

• Over five years: Only about 28% of patients met the 80% standard for the entire five years.
• Year by year: In any single year, 59% to 75% met the standard, meaning many people took breaks or stopped at some point.
• Skipping radiation: People who did not have radiation were twice as likely to have their medication on hand less than half the time, and they were also more likely to fall below the 60% and 70% marks.
• Age: People younger than 60 had a 20% to 25% higher risk of not staying on their medication.

Lead author Dr. Shannon Jiang, a radiation oncology resident at Washington University, noted that a prescription for five years of endocrine therapy is not the same as a patient taking it for five years.

Why This Matters if You're Considering Skipping Radiation

The clinical trials that support skipping radiation for some lower-risk patients assume those patients continue endocrine therapy for several years. If the pills are stopped early, a person may end up with neither of the two treatments meant to keep cancer from coming back in the breast.

Dr. Jose G. Bazan of City of Hope, who chairs ASTRO's breast cancer resource panel, said doctors should weigh radiation's benefit in controlling cancer in the breast alongside the practical realities of staying on endocrine therapy.

The study has limits. Refill records show whether people had their pills, not whether they took them, and they don't explain why people stopped. The study also didn't include people 65 and older, who are the group most often offered the choice to skip radiation, so the researchers plan to repeat the analysis with Medicare data.

Side Effects Are a Common Reason People Stop

Endocrine therapy can cause hot flashes, fatigue, joint pain, effects on bone health and trouble with memory or concentration. These side effects are real, and they are one of the main reasons people struggle to stay on treatment.

If side effects are wearing you down, tell your care team before stopping on your own. There may be ways to manage them or a different endocrine therapy to try. For some people, genomic testing can also help clarify how long treatment is needed. CURE explored this in Could a Genomic Test Spare You Extra Years of Hormone Therapy?

Questions to Ask Your Care Team

• Am I a candidate to skip radiation? What is my risk of the cancer coming back with and without it?
• If I skip radiation, how important is it that I take endocrine therapy every day for the full course?
• What can we do if side effects make it hard to keep taking my medication?
• Could I switch to a different endocrine therapy if the one I'm on isn't working for me?

References

1. Newswise. "Real-World Data Indicate Lower Adherence Rates for Breast Cancer Endocrine Therapy When Radiation Therapy Is Omitted." Sept. 27, 2026.
2. News-Medical. "Long-Term Endocrine Therapy Adherence Remains Low After Breast Cancer Surgery." Sept. 27, 2026.
3. American Society for Radiation Oncology. "ASTRO to Showcase Advances in Radiation Medicine and Cancer Research in 2026 Annual Meeting Press Program." September 2026.

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