The Genetic Basis of Transcriptional Heterogeneity for Basal-Like Features in Pancreatic Ductal Adenocarcinoma

Abstract Pancreatic cancer expression profiles largely reflect a classical or basal-like phenotype. The extent to which these profiles vary within a patient is unknown. We integrated evolutionary analysis and expression profiling in multiregion sampled metastatic pancreatic cancers, finding that squamous features are the histologic correlate of an RNA-seq defined basal-like subtype. In patients with coexisting basal/squamous and classical/glandular morphology, phylogenetic studies revealed that squamous morphology represented a subclonal population. Cancers with squamous features were significantly more likely to have truncal mutations in chromatin modifiers, intercellular heterogeneity for MYC amplification, and entosis. These data provide a unifying paradigm for integrating basal-type expression profiles, squamous histology, and somatic mutations in chromatin modifier genes in the context of clonal evolution of pancreatic cancer. One Sentence Summary Basal type expression profiles in pancreatic cancer have a clonal basis rooted in genetic alterations of chromatin modifier genes.