Despite the widespread use of mammography for breast cancer screening, breast cancer remains the most common cause of cancer-related mortality among women worldwide. The identification of biomarkers that identify cancers when they are small, localized and most treatable is an important aim of current breast cancer research. Biomarkers need to be sensitive, specific, reproducible and easily collected from patients from readily accessible tissue or body fluids. While conventional biomarker research has focused on soluble proteins, cell markers, proteomics and DNA methylation, much progress has also been made in the field of immunobiomarkers and multiparameter gene arrays. Currently, no one biomarker has demonstrated sufficient sensitivity and reproducibility for independent clinical and commercial use. This review summarizes the current state of breast cancer biomarker research and anticipated future directions.