Updated project metadata. Aberrant activation of the ERK signaling pathway triggers a protective anticancer response characterized by stable growth arrest and activation of tumor suppressors called cellular senescence. Pancreatic adenocarcinomas (PDAC) often possess mutations in K-Ras that activate the ERK pathway. Pancreatic intraepithelial neoplasia of low degree display high levels of phospho-ERK consistent with senescence acting as a barrier for malignant transformation. However, advanced lesions downregulate phospho-ERK levels circumventing the senescence barrier. Restoring ERK hyperactivation in PDAC using an activated allele of the kinase RAF, leads to ERK-dependent growth arrest with senescence biomarkers. Phosphoproteomics analysis of ERK-dependent senescence in PDAC revealed a decrease in several nucleolar phosphoproteins suggesting that high levels of ERK lead to senescence via nucleolar stress. Consistent with this explanation, ERK-dependent senescent cells displayed intranucleolar foci containing RNA polymerase I. Combining ribosome biogenesis inhibitors with ERK hyperactivation reinforced the senescence response of PDAC cells. The drug cocktail FOLFIRINOX, currently the best treatment for PDAC, also triggered ERK hyperactivation and nucleolar stress characterized by nucleolar foci, solid amyloid aggregates and a decrease in 5.8S and 28S rRNAs. We thus suggest that drugs targeting ribosome biogenesis can improve the senescence anticancer response in pancreatic cancer.