Interleukin-6 Secreted from Cancer-associated Fibroblast Inhibits Cancer Growth in Biliary Tract Cancer

Cancer-associated fibroblasts (CAFs) are key components of the tumor microenvironment and can either promote or suppress tumor growth. This study aimed to identify CAFs that inhibit proliferation in biliary tract cancer (BTC) cell lines and explore the underlying mechanisms. Three BTC cell lines and one pancreatic cancer cell line were treated with conditioned media (CM) from CAFs isolated from BTC specimens. Cell proliferation was assessed, and cytokine profiles in CM were analyzed using protein arrays. Expression of interleukin-6 (IL-6) pathway proteins was examined via western blot and immunohistochemistry (IHC) in BTC tissues. Survival outcomes were analyzed using Kaplan-Meier curves. Some BTC-derived CAFs suppressed cancer cell growth. IL-6 was identified in the CM as a key inhibitory cytokine. IL-6 treatment significantly reduced BTC cell proliferation, accompanied by increased suppressor of cytokine signaling 3 (SOCS3) and decreased activator of transcription 3 (STAT3) expression. In BTC patient tissues, stromal IL-6 expression correlated with improved relapse-free survival (RFS; 60.8 vs. 18.5 months, p=0.008) and overall survival (OS; 61.6 vs. 33.9 months, p=0.05). Patients with positive expression of IL-6 receptor subunits CD130 and CD126, as well as SOCS3, had significantly longer RFS and/or OS compared to negative cases. For CD130, median RFS and OS were 60.8 vs. 17.4 months (p=0.02) and 60.7 vs. 34.6 months (p=0.05), respectively. For SOCS3, RFS and OS were 60.8 vs. 21.1 months (p=0.05) and 51.6 vs. 34.8 months (p=0.04). CD126 positivity was associated with longer RFS (60.8 vs. 21.1 months, p=0.04), but OS did not differ significantly. A subset of CAFs in BTC has tumor-suppressive activity mediated by IL-6, which inhibits cancer cell proliferation via the SOCS3/STAT3 pathway and correlates with better clinical outcomes.