Secretion of high amounts of hepatocyte growth factor is a characteristic feature of cancer‐associated fibroblasts with EGFR‐TKI resistance‐promoting phenotype—A study of 18 cases of cancer‐associated fibroblasts

: Humoral factors from cancer-associated fibroblasts (CAFs) reportedly affect epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) resistance in cancer cells with EGFR mutations. The aim of this study was to identify the robust humoral factors secreted from CAFs that induce the primary resistance to EGFR-TKI. We evaluated the EGFR-TKI sensitivity of EGFR-mutant lung adenocarcinoma cell line (PC-9) treated with condition media (CM) from 18 cases of CAFs and matched non-cancerous-tissue-associated fibroblasts (NCAFs). We measured the expression levels of hepatocyte growth factor (HGF), interleukin-6, fibroblast growth factor-2, insulin-like growth factor-1, and vascular endothelial growth factor-A in CAFs and NCAFs. We examined whether HGF neutralizing antibody could annul the EGFR-TKI resistance induced by CM from CAFs. Compared to CM from NCAFs, CM from CAFs increased the resistance of PC-9 cells to EGFR-TKI in five out of 18 cases. Relative expression ratio of HGF messenger RNA was significantly higher in these five CAFs compared to others (P = 0.0013), whereas other cytokines were not. In four of these five cases, the addition of HGF neutralizing antibody significantly decreased the survival ratio of PC-9 cells. This study suggests that the secretion of higher amounts of HGF is the robust feature of EGFR-TKI resistance-promoting CAFs.