Gene expression profiling is a laboratory technique used to measure the activity of thousands of genes at once. This process helps researchers understand which genes are turned on or off in a particular cell type or condition, such as a disease. By analyzing the patterns of gene expression, scientists can gain insights into how cells function and respond to various stimuli. This technique is particularly useful in cancer research, where it can identify specific gene expression patterns associated with different types of tumors. Such information can guide treatment decisions and help predict patient outcomes, ultimately leading to more personalized medical approaches.