CAFs secrete ECM and soluble factors that stimulate cancer progression, and are believed to be derived from mesenchymal cells of different origins that are resident or recruited to the pancreas by neoplastic cells (Öhlund et al., 2014; Moffitt et al., 2015; Kalluri, 2016). A major source of CAFs in PDA is pancreatic stellate cells (PSCs), which are resident mesenchymal cells of the pancreas that store lipid droplets and express fibroblast-activation protein α (FAP; Bachem et al., 2005; Erkan et al., 2012; Apte et al., 2013; Moir et al., 2015).
I believe that this segment highlights key information to understand for the rest of the paper. CAFs are the main focus of this paper, so we now have a basic understanding of what they do, and where they come from. The note that in PDA they are believed to be specifically derived from PSCs is also key.