Overcoming endocrine resistance in metastatic hormone receptor-positive breast cancer.

Endocrine therapy has historically formed the basis of treatment of metastatic hormone receptor-positive breast cancer. The development of endocrine resistance has led to the development of newer endocrine drug combinations. Use of the CDK4/6 inhibitors has significantly improved progression-free survival in this group of patients. There are multiple studies of the use of P13K inhibitors and mTOR inhibitors for use as subsequent lines of therapy, particularly for endocrine resistance. The optimal sequencing of therapy should be based on medical comorbidities, prior adjuvant therapies, quality of life, side-effect profile, and disease-free interval.