FAP and lung cancer: A typical fibroblast marker (FAP) was identified in gene set 1 together with fibroblast-expressed extracellular matrix-associated genes, such as collagens, whereas gene set 13 contained complement factor C1Q. FAP has been identified as a prognostic marker in various cancer studies, including breast and lung cancer, and has been suggested to be a potential target in solid tumors [37-40].