Multiparameter gene expression tests for breast cancer evaluate specific groups of genes in malignant tumor tissue in order to predict prognosis, recurrence, and metastasis of the cancer, as well as to guide treatment. These tests are ultimately aimed at developing a personalized approach to patient care. Cancers represent uncontrolled growth of abnormal cells. Each breast cancer has its own genetic makeup that is distinct from the normal tissue surrounding it. Genes in the tumor regulate how rapidly it will grow, its likelihood of metastasizing and moving throughout the body, whether or not its growth is supported by estrogen or progesterone, whether it over-expresses certain proteins such as Her-2/neu, and how responsive it will be to different treatments.

Regulation of tumor genes is accomplished through gene expression – the timing and quantity of production of gene-specific ribonucleic acid (RNA) and proteins. Gene expression patterns include both the increase and/or decrease in the expression of genes (upregulation and downregulation) that are responsible for the production of proteins. Multiparameter gene expression tests measure the products of multiple tumor genes at the same time. The result is a pattern of gene expressions that are consolidated into a score. The score is then used to help predict the likely behavior of the tumor.