Breast Cancer Patients Often Stop Endocrine Therapy

A new study shows that fewer than 30 percent of patients maintain adherence to medication five years after a lumpectomy.

Updated on Oct. 16, 2026 in Cancer

Isometric editorial illustration showing a diminishing geometric arrangement of identical pharmaceutical tablets, representing declining medication adherence over time. — A new study indicates that fewer than 30 percent of patients maintain endocrine therapy adherence five years after their breast cancer lumpectomy. AI Illustration. Upload story photo >

Live Poll

Do you find it difficult to maintain a long-term medication schedule prescribed by your doctor?

Researchers found that adherence to prescribed endocrine therapy drops significantly among women with ER-positive early-stage breast cancer. By the five-year mark following a lumpectomy, less than 30 percent of patients remain fully adherent to their treatment regimens.

Why it matters

Low adherence to long-term endocrine therapy can compromise recovery outcomes for breast cancer patients. Understanding these patterns helps healthcare providers identify which patients may require additional support to complete their prescribed courses.

The study tracked 17,025 women, finding that 34.6 percent of patients were adherent in year one, while 77 percent of those who remained on therapy met adherence thresholds in years two through five.

The players

ASTRO

The American Society for Radiation Oncology is a professional medical association that hosts annual meetings to share clinical research.

Washington University School of Medicine

This academic institution based in St. Louis conducts medical research and provides patient care.

The details

Using medication possession ratios, investigators analyzed claims data to measure adherence following lumpectomy procedures. Results indicated that patients younger than 60 years showed a lower hazard of nonadherence, while those receiving adjuvant radiation therapy were more likely to maintain their medication schedules.

September 26 to 30, 2026: The study was presented at the ASTRO annual meeting.
Year 1: 34.6 percent of patients remained adherent to therapy.
Years 2 to 5: 77 percent of remaining patients met adherence thresholds.
Year 5: Fewer than 30 percent of patients remained adherent.

Health Landscape

This research quantifies a critical hurdle in meeting the clinical standard of five-year endocrine therapy duration for ER-positive breast cancer. It reveals a pattern of attrition that suggests current treatment protocols may be difficult for many patients to sustain.

Patients may benefit from discussing potential barriers to medication adherence with their oncologists to ensure long-term treatment success. Managing side effects or scheduling concerns early can play a key role in helping individuals remain on their prescribed therapy.

The takeaway

Maintaining long-term adherence to endocrine therapy is essential for managing early-stage breast cancer outcomes. Patients should proactively communicate with their healthcare teams if they encounter difficulties staying on their medication schedule.