The profiling begins when researchers take brain tumor samples and purify all of the genes expressed by extracting the RNA, a subset of genes in the human genome. They then label the RNA with florescent markers. The marked genes are used to create a gene expression profile through a process called micro-arraying. Using this process, researchers can see up to 40,000 genes at once. The marked or tagged genes from the brain tumor samples can be overlaid on the micro-array of normal tissue samples, and Nelson and his team can compare the patterns to determine which genes are turned on and which are turned off in the tumor samples.
Researchers can then correlate the differences in their database.
For example, if a tumor sample from a brain cancer patient who responded well to radiation and a tumor sample from a patient who did not respond to radiation are compared, researchers can note differences in the gene expression patterns that may explain the disparate responses to therapy. Further, if they get similar gene expression patterns from the tumor samples of 200 patients who did not respond to radiation, that information can be used to choose what may be a more effective treatment. Ultimately, looking at the expression patterns of thousands of genes in a variety of brain tumor samples is expected to help researchers predict how certain tumors will respond to treatment. That information can be used in making treatment decisions later for other brain cancer patients, Nelson said. Unfortunately, a brain cancer diagnosis often is viewed as a death sentence.