There is a large amount of gene expression data that exists in the public domain. This data has been generated under a variety of experimental conditions. Unfortunately, these experimental variations have generally prevented researchers from accurately comparing and combining this wealth of data, which still hides many novel insights.
Licamele, L., & Getoor, L. (2010). Indirect two-sided relative ranking: A robust similarity measure for gene expression data. BMC Bioinformatics, 11. https://doi.org/10.1186/1471-2105-11-137