COL1A1 and cancer: Given the results that ECM-related pathways were up-regulated in PHLDA2-H subgroup, in which cancer associated fibroblast (CAF) plays a vital role, we then investigated the association between PHLDA2 and CAF, and observed positive correlations between the expression level of PHLDA2 and all CAF markers, including ACTA2 (r = 0.337, p < 0.001), MYH11 (r = 0.231, p < 0.001), COL1A1 (r = 0.433, p < 0.001), COL1A2 (r = 0.405, p < 0.001), TAGLN (r = 0.385, p < 0.001), PDGFRB (r = 0.359, p < 0.001) (Fig. 5G–L).