Every breast cell has a complete set of an individual’s DNA and is contained in the nucleus of the cell. The DNA is unfolded and refolded constantly so that the information contained within the DNA sequences can be used to regulate processes within the cell required for cell growth and cell function, including cell death at the appropriate time. Specific genes are expressed at different times throughout the life of the woman. For example: genes coding for proteins used to increase the size of the breast or for milk production are expressed to varying degrees depending on the hormonal status of the woman. Mistakes are often made; fortunately, DNA contains code for dealing with mistakes including an autodestruct code if the mistakes are not recoverable. Some genetic mutations lead to increased or decreased expression of certain genes. The cell is affected by the tissue around it and is influenced by a multitude of environmental and internal factors, some of which lead to mutations within the DNA. These changes (mutations) if not quickly identified and corrected may cause cancer.
Every breast cancer is due to genetic mutations within a breast cell. Breast cancer genomics is the study of the gene expression and genetic errors specific to the cancer causing cells. The specific changes and genes expressed are evaluated by laboratory analysis of the DNA within the tumor and add to the understanding the biologic behavior of the tumor. This is useful in predicting aggressiveness of a tumor and likelihood of metastasis (the movement of breast cancer tumor cells out of the breast and into other parts of the body). The genomic analysis of a breast cancer can also help in predicting likelihood of response to systemic chemotherapy or endocrine therapy. The degree of expression of the estrogen and progesterone receptors has been valuable in the classification of tumors and prediction of tumor behavior for decades. The current evaluation of breast cancer tumors includes genomic profiling of many more genes, thereby increasing the ability to personalize cancer care based on the specific profile of the patient’s breast cancer. The understanding of breast cancer genomics is so impactful that it is now being incorporated into the newest version of the breast cancer staging guidelines. It is very important to understand that this genomic information is important and still new in the treatment of breast cancer. More research is being done to know how to use this information.