Nuclear active RSK2 (magenta, left) correlates with ERα (blue, right) in sixty percent of ER⁺ patients as visualized in this serial section from an ER⁺ tumor. In each section the cells were also stained for cytokeratin 8 (lime, left; magenta, right) and cytokeratin 14 (cyan, left; yellow, right). In the left image, cells that are positive for both K8 and K14 are teal and on the right, these dual-positive cells are orange. Sequestration of RSK2 by ERα in the nucleus drives a pro-neoplastic transcriptional program critical to the ER⁺ lineage in the mammary gland, neoplasia, and differing patient responses to antiestrogen therapies. For details, see article by Ludwik and colleagues on page 2014.