Advancements in ER-Positive Breast Cancer

The estrogen receptor (ER)—positive subtype is the most common subset of breast cancer in both early-stage and late-stage disease worldwide, notes Hope S. Rugo, MD. Advances in the understanding of ovarian suppression via surgery or medications has further improved outcomes for many patients with ER-positive breast cancer. However, hormone therapy is not effective for every individual with hormone receptor–positive disease, says Rugo.

Developments in HER2—negative, ER-positive disease include the introduction of the mTOR inhibitor everolimus. In the phase III BOLERO-2 study, the addition of everolimus to exemestane demonstrated more than doubling of progression-free survival (PFS) versus exemestane alone in patients with metastatic disease who progressed on nonsteroidal aromatase inhibitors (median PFS 10.6 vs 4.1 months; HR = 0.36). Toxicities include stomatitis, which may be managed with a steroid mouthwash, Rugo suggests.

Many types of tumors, and particularly ER-positive breast cancer, require cyclin-dependent kinase (CDK) to divide, proliferate, and metastasize. Combining palbociclib, a CDK4/6 inhibitor, with fulvestrant may help individuals with resistant disease. Data from PALOMA-3 showed a doubling of PFS with the addition of palbociclib to fulvestrant in patients whose disease progressed on or following endocrine treatment. Additionally, there was no increased rate of febrile neutropenia or infections, adds Rugo.