What is gene expression?
Gene expression is the process of making specific proteins from the information contained in the genes. Different tissues express different sets of genes based on their role in the body. The information from the gene is put together to make a template for building ribonucleic acid (RNA). RNA then undergoes specific modifications to create the protein required by the cell. Gene expression tests evaluate the RNA in a person's tissue sample to determine which genes are actively making proteins.
What are multiparameter tests?
Unlike many standard laboratory tests that evaluate or measure one analyte at a time, multiparameter tests evaluate many analytes at the same time. Results are typically interpreted together, not individually, and in relation to one another. This type of test is also called multiplex testing. The development of new technologies, such as microarrays, has advanced the use of these types of tests.
What are breast cancer multiparameter gene expression tests?
These are tests that evaluate the products (RNA) of specific groups of genes in malignant tumor tissue from the breast in order to determine which genes are making proteins in the tumor tissue. This information is used to predict prognosis by estimating risk of recurrence, and spread (metastasis) of the cancer, as well as to guide treatment. These tests are relatively new, but their use is increasing. They are ultimately aimed at developing a personalized approach to patient care and breast cancer therapy.
Cancers represent uncontrolled growth of abnormal cells that arise due to multiple factors, including malfunctioning proteins that normally keep cell growth in check. The proteins usually malfunction as a result of an acquired mutation in the DNA that contains the instructions for making the proteins. As noted above, genes control the production of RNA. RNA controls the production of proteins, and proteins in turn promote and regulate growth and the rate of reactions in the body. This entire process is referred to as gene expression. Many cellular processes are comprised of a series of steps, with key enzymes (specialized proteins) required to move through each step. Mutations in key genes may result in changes to how a step proceeds (or doesn't) and may cause a change to the end product or any intermediate product along the pathway.
Genetic mutations can result in abnormal or absent protein, which in turn may lead to unregulated cell growth and division, eventually causing them to invade healthy tissues and become cancerous. Normally, there is a delicate balance between cells, but cancer cells can often "invade" and take over other tissues and may not undergo programmed cell death as they should when growing out of control. Cancer cells and tumors are genetically different from the healthy cells around them.
Each individual breast cancer has different genetic mutations that distinguishes it from the normal tissue. The mutation(s) in cancer cells and the change to the expression of those genes regulate how rapidly the tumor grows, its likelihood of metastasizing and moving throughout the body, whether or not its growth is supported by the hormones estrogen or progesterone, whether it over-expresses certain proteins such as HER2, and how responsive it will be to different treatments.
Through gene expression, breast tumor genes regulate the timing and quantity of production of gene-specific RNA and proteins. Patterns in gene expression include both the increase and/or decrease in the expression of genes (upregulation and downregulation) that are responsible for the production of RNA and proteins. Rather than evaluating a single gene, multiparameter gene expression tests analyze the RNA of multiple genes in a tumor at the same time. The result is a pattern of gene expression that is consolidated into a score and/or profile. This information is then used to help predict the likely behavior of the tumor and its response to treatment.