Young Women With Early-Stage Breast Cancer Can Benefit From Extending Post-Treatment Hormone Therapy Beyond 5 Years

Extending post-treatment endocrine therapy can benefit young women who are still premenopausal after initial treatment for early-stage, node-positive, hormone receptor (HR)-positive breast cancer and have already taken five years of post-treatment endocrine therapy, according to an analysis of real-world, observational data led by Dr. Ann Partridge, vice chair of the Department of Medical Oncology at Dana-Farber Cancer Institute. Women who remained on endocrine therapy for more than five years post-treatment were 51% less likely to relapse, the study found.

Rates of breast cancer in young women aged 40 or younger have been steadily increasing worldwide over the past 20 years. Relapse after treatment is more likely in younger women, particularly for HR-positive early breast cancer, the most common type of the disease.

“These findings provide much needed data to help to inform current care that continuing endocrine therapy in young women with higher risk early breast cancer may reduce risk of recurrence,” says Partridge. “When women are tolerating therapy in the higher risk disease setting, it is reasonable to extend endocrine therapy for potential benefits.”

The use of post-treatment adjuvant endocrine therapy with tamoxifen plus ovarian function suppression for five years reduces the risk of relapse in premenopausal women, according to earlier clinical research. Additional trials have shown that extending adjuvant tamoxifen to 10 years decreases the risk of death from breast cancer in both pre- and post-menopausal women.

However, in premenopausal patients with high-risk, HR-positive early breast cancer who are treated for five years with ovarian function suppression plus an aromatase inhibitor, studies suggest that the risk of recurrence outside of the breast is near 25% after 15 years. “There is an urgent need to reduce late recurrences by optimizing endocrine therapy in this group,” says Partridge.

This observational study performed an analysis of two real-world data sets: The Young Women’s Breast Cancer Study and the Institute of Oncology Breast Cancer cohort. The analysis included women diagnosed with early breast cancer at or before age 40 who were treated with surgery, had node-positive, non-metastatic disease, and were HR-positive. Patients also had to have completed five years of adjuvant endocrine therapy with ovarian function suppression, have no evidence of recurrence at the time of completion, and be premenopausal at the time of completion.

Partridge and colleagues compared outcomes of patients who initiated extended endocrine therapy beyond five years to those who did not. Extended endocrine therapy could include tamoxifen alone, ovarian function suppression plus tamoxifen, or plus an aromatase inhibitor.

Median duration of extended endocrine therapy was 3.7 years, and median follow-up was 7.3 years. The team found that extending endocrine therapy beyond five years was associated with a clinically meaningful reduction in risk of an invasive breast cancer recurrence in premenopausal patients with node-positive HR-positive early breast cancer. The practice also improved distant recurrence-free survival.

The groups also showed no differences in bone fractures, major cardiovascular effects or deaths unrelated to recurrence. These findings are consistent with previous clinical trials.

“Real world studies of observational data have limitations, so we need to confirm these findings prospectively,” says Partridge. “But these data help inform care today and future research.”