Endocrine therapy resistance in estrogen receptor (ER)-positive breast cancer

• Endocrine treatment resistance in estrogen receptor positive breast cancer.
• Technological advancements for the discovery of biomarkers of endocrine resistance.
• Opportunities and restrictions of biomarkers in the clinical laboratory.

Estrogen receptor (ER)-positive breast cancer represents the majority (∼70%) of all breast malignancies. In this subgroup of breast cancers, endocrine therapies are effective both in the adjuvant and recurrent settings, although resistance remains a major issue. Several high-throughput approaches have been used to elucidate mechanisms of resistance and to derive potential predictive markers or alternative therapies. In this review, we cover the state-of-the-art of endocrine-resistance biomarker discovery with regard to the latest technological developments, and discuss current opportunities and restrictions for their implementation into a clinical setting.