A gene signature is a specific pattern of gene expression that is used to predict certain characteristics or outcomes in a cell, tissue, or organism. Gene signatures can be identified through the analysis of gene expression data from various sources, such as microarray or RNA sequencing data. These signatures can be used to classify different subtypes of diseases, predict response to treatment, or identify biomarkers for early detection of disease. Gene signatures are a powerful tool in personalized medicine and can help guide patient treatment decisions based on their individual genetic profile.