Gene expression profiling is a powerful technique used to measure the activity of thousands of genes at once to create a global picture of cellular function. This method uses high-throughput technologies such as microarrays or next-generation sequencing (NGS) to determine the expression levels of numerous genes simultaneously. In the context of cancer, gene expression profiling is crucial for understanding the molecular mechanisms driving tumorigenesis and for identifying potential biomarkers for diagnosis, prognosis, and treatment.