Breast cancer is a common and often deadly disease.
According to the National Cancer Institute, more than 192,000 women in the United States are diagnosed with breast cancer every year. In the quest for better treatments for this lethal disease, scientists have turned increasingly to new approaches made possible by recent advances in genetics. Among these is a molecular biology tool called a microarray. Some controversy persists about the extent to which microarrays can determine prognosis or treatments for patients with breast cancer.
Microarrays
A single-stranded piece of DNA will bind or stick to another single strand with a matching or complementary sequence. This basic principle makes the microarray possible. Several variations exist, but all involve the same idea. Thousands of probes (short single-stranded pieces of DNA) are affixed to a solid surface. A DNA sample is labeled with fluorescent tags, molecules that glow or re-emit light when exposed to certain frequencies. The sample is added to the solid surface under conditions that help the sample bind to the probes. If a particular site on the microarray glows or emits light, the sequence of the probe is present in the sample.
Uses of Microarrays in Breast Cancer
Microarrays are often used to compare genetic variations at hundreds or even thousands of specific sites across the genome. By collecting DNA samples from many people with and without a disease, researchers can carry out a genome-wide association study (GWAS) to test for genes that might increase the risk of developing the disease. Gene-expression profiling is another common use in breast cancer research; scientists use a microarray to determine which genes are "switched on" or expressed in the cancer cells and compare these results with other cancer patients or with healthy cells.
Past Research
A study published in the journal "Nature" in 2002 found evidence that suggested gene expression profiles could help determine a patient's prognosis--the chances that her cancer might metastasize or grow more rapidly. Subsequent studies reached similar conclusions. Numerous subsequent studies have found ways to classify breast cancers based on their gene-expression profile; some profiles may respond better to certain types of treatment than others. Various studies have found that breast cancers with specific gene-expression profiles seem to be more susceptible to particular chemotherapy drugs.
Significance
Using gene-expression profiling with microarrays, it may be possible to distinguish breast cancers that require chemotherapy and surgery from cancers that require surgery alone and thereby to minimize the side effects associated with treatment. It may also become possible to select treatments for a patient based on the gene-expression profile of her cancer.
Considerations
Other authors have criticized the results of this research. A 2005 review in "Breast Cancer Research," for example, cited several flaws and limitations in past studies. Scientists are still trying to determine which gene-expression profiles can help predict outcome or determine treatment. Nonetheless, microarrays are a powerful technique for studying breast cancer, although further research is required to bring the promise of this technique to fruition.
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