Breast Cancer Multiparameter Gene Expression Tests

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Also known as: Breast Cancer Gene Expression Tests; Breast Cancer Gene Expression Profiling

What is gene expression?

Gene expression is the translation of genetic information from genes to proteins that results in the characteristics that cells and tissues exhibit. Genes are the basic units of DNA that code for the production of proteins. Genes are made up of nucleotides, which are composed of phosphates, a sugar, and one of four different nitrogen-containing bases: adenine, guanine, thymine, or cytosine. The arrangement of the bases in each gene is used to produce RNA, which in turn produces a protein. Gene expression tests evaluate the RNA in a person's sample of tissue to determine its characteristics.

What are multiparameter tests?

Unlike many standard laboratory tests that evaluate or measure one analyte at a time, multiparameter tests evaluate many analytes together 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. 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 predict prognosis, 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 codes for the proteins. As noted above, the genes that make up DNA control the production of RNA. RNA controls the production of proteins that in turn promote and regulate growth and the rate of reactions in the body, and this is referred to as gene expression. The reactions typically take place in a series of steps, with key enzymes required to move along the reaction pathway. Mutations in genes may result in changes in the steps, the enzymes, and/or the pathway in characteristic ways. Sometimes the changes result in the excess or malfunction of a protein that regulates growth, resulting in uninhibited growth of cells.

Genetic mutations and the expression of the mutations can lead to unchecked growth and division of cells, eventually causing them to become cancerous. They can invade other tissue and may not die as other cells do. Cancer cells and tumors are genetically different from the normal cells around them.

Different types of breast cancer have different genetic alterations that distinguish them from the normal tissue. The mutated genes in the tumor, and the expression of those genes, regulate how rapidly the tumor will grow, 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 tumor genes 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.

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