PECAM1 and lung cancer: To optimise fibroblast identification, we excluded immune (CD45+), epithelial (EpCAM+) and endothelial (CD31+) cells, and compared the expression of three previously-described fibroblast surface markers (PDGFR-α and -β, CD90) in foetal lung (IMR-90) and skin (HFFF2) fibroblasts and also a lung cancer cell line (H441).