Activating mutations in K-Ras occur in most pancreatic cancers. We investigated whether genetic changes (K-Ras mutations) in human pancreatic cancer cell lines altered genomic instability and epigenetic events responding to Ras-mitogen activated protein kinase (MAPK) signaling by characterizing 3 human pancreatic cancer cells lines with and without activating mutations in K-Ras. Activation of the Ras-MAPK pathway results in the stimulation of the histone H3 kinase, mitogen and stress activated kinase (MSK) 1, and increased phosphorylation of histone H3 at serine 10 (H3 S10ph). MSK1 and H3 S10ph have roles in neoplastic transformation. We demonstrate that the presence of a K-Ras mutation did not correlate with elevated chromosomal aberrations or increased genomic instability. Although the levels of the epidermal growth factor receptors and MSK were similar, the Ras-MAPK pathway was differentially induced by phorbol esters (12-O tetradecanoylphorbol-13-acetate) or epidermal growth factor, with the response of this signaling pathway being cell-type specific. This response corresponded downstream at the level of chromatin where stimuli-induced elevation of H3 S10ph typically paralleled the increase in phospho-extracellular signal regulated kinase 1/2. Our results present evidence that nonclonal chromosomal aberrations and epigenetic programming responding to stimulation of the Ras-MAPK pathway may be better markers for cancer progression than the upstream mutated oncogenes. © 2008 Wiley-Liss, Inc.