Breast cancer is not a unique disease; its heterogeneity has been known for decades. The major advances in breast cancer therapy are due to our recognition of this heterogeneity, and our acknowledgment that an efficacious therapy “on average” might not be the optimal therapy for a given patient.
In early and advanced disease, tumor biology is becoming the main determinant of treatment selection, rising above disease stage and other clinical parameters. In daily practice, the expression level of hormone receptor and HER2 is the core of every breast cancer diagnosis. These parameters are prognostic and predictive of treatment efficacy. Nowadays, endocrine therapy is the mainstay of treatment for hormone receptor-positive tumors, and anti-HER2 agents have dramatically improved the prognosis of HER2-positive breast cancer patients.
However, tumor biology is extremely complex, and redundant pathways as well as crosstalk between different pathways are responsible for treatment resistance. With newer technologies it is now possible to study these pathways, and our knowledge of breast cancer heterogeneity is growing day by day.
This issue of Hot Topics in Oncology focuses on the molecular basis of endocrine therapy resistance, and on the clinical strategies to overcome resistance to hormonal therapy.