Immunofluorescence imaging of CK2α and Rab11 in human A549 lung adenocarcinoma cells treated with the endocytosis inhibitor, Dynasore. Visualization of KSR1, p-ERK, CK2α, and other RAS pathway proteins revealed their perinuclear cytoplasmic localization in tumor cells. These “perinuclear signaling complexes” (PSC) are induced upon RAS pathway activation, reside on perinuclear endosomes, and can be disrupted by endocytosis inhibitors. PSCs appear to be a defining feature of most or all cancer cells and regulate RAS signal transmission to downstream targets. For details, see article by Basu and colleagues on page 891.