Current research topics in endocrine therapy for breast cancer.

There are large-scale molecular differences between estrogen receptor (ER)-positive and ER-negative breast cancers. Endocrine therapy has become the most important treatment option for women with ER-positive breast cancer, and approximately 70% of primary breast cancers express ERalpha. Endocrine therapy has provided meaningful advances in breast cancer treatment and prevention. However, some patients continue to develop recurrence and die of the disease. New insights into ER biology and progress in the understanding of resistance mechanisms are generating tremendous promise for new therapeutic opportunities to target resistance and improve disease outcomes.