The Emerging Role of ESR1 Mutations in Luminal Breast Cancer as a Prognostic and Predictive Biomarker of Response to Endocrine Therapy

Endocrine-Resistant Breast Cancer: Mechanisms and Treatment

BACKGROUND

Endocrine treatment is one of the most effective therapies for estrogen receptor-positive breast cancer. However, most tumors will develop resistance to endocrine therapy as the cancer progresses. This review focuses on the mechanisms and markers of endocrine-resistant breast cancer. In addition, current and future strategies to overcome endocrine resistance are discussed.

SUMMARY

Several molecular mechanisms of endocrine resistance have been identified, including alterations in the ESR1 gene or in the PIK3CA/mTOR pathway. Meanwhile, CDK4/6, mTOR, and PI3K inhibition have shown to improve the efficacy of endocrine treatment and new promising approaches are being developed.

KEY MESSAGE

Overcoming primary or acquired resistance to endocrine treatment remains a major challenge. Since the molecular mechanisms of endocrine resistance are manifold, optimal combination and sequencing strategies will have to be developed in the future.