While future investigations are required to establish the connection between KDM4B and ER+ breast cancer survival, these results illustrate a successful utilization of true archival FFPE tissues for potentially clinically relevant biomarker identification by RNA-seq and is, to our knowledge, the first report of differential expression and activity of KDM4B within ER+ breast cancers correlating to patient survival. This evidence concerns the gene KDM4B and breast carcinoma.