Biological markers of invasive breast cancer.

Biological markers for breast cancer are biomolecules that result from cancer-related processes and are associated with particular clinical outcomes; they thus help predict responses to therapy. In recent years, gene expression profiling has made the molecular classification of breast cancer possible. Classification of breast cancer by immunohistochemical expression of estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2 and Ki-67 is standard practice for clinical decision-making. Assessments of hormone receptor expression and human epidermal growth factor receptor 2 overexpression help estimate benefits from targeted therapies and have greatly improved prognoses for women with these breast cancer types. Although Ki-67 positivity is associated with an adverse outcome, its clear identification is an aid to optimal disease management. Standardization of testing methodology to minimize inter-laboratory measurement variations is a remaining issue. Multi-gene assays provide prognostic information and identify those most likely to benefit from systemic chemotherapy. Incorporating molecular profiles with conventional pathological classification would be more precise, and could enhance the clinical development of personalized therapy in breast cancer.