Association between high expression of intratumoral fibroblast activation protein and survival in patients with intrahepatic cholangiocarcinoma

BACKGROUND: Cancer-associated fibroblasts (CAFs) have been reported to exhibit protumorigenic effects. Among the well-known CAF markers such as smooth muscle actin (SMA) and fibroblast activation protein (FAP), high expression of SMA in the peritumoral stroma has been reported to be a prognostic factor in various cancers. However, the effect of high FAP expression in intrahepatic cholangiocarcinoma (IHCC) has not been fully clarified. We evaluated the expression of CAF markers, focusing on FAP expression in the peripheral and intratumoral regions, to clarify the association with survival in patients with IHCC. METHODS: The study cohort comprised 37 patients who underwent curative resection for IHCC. The FAP expressions were evaluated in the peripheral and intratumoral regions of the resected tissues. Clinicopathological factors and survival outcomes were investigated between patients with high versus low FAP expression. Uni- and multivariate analyses were performed to identify the prognostic factors for overall survival and relapse-free survival. RESULTS: The median area percentages of FAP expression in the peripheral and intratumoral regions were 15.5% and 17.8%, respectively. High FAP expression in the intratumoral region was significantly associated with worse overall survival and disease-free survival than low FAP expression in the intratumoral region. Multivariate analysis identified high intratumoral FAP expression as a risk factor for worse overall survival (hazard ratio, 2.450; p = 0.049) and relapse-free survival (hazard ratio, 2.743; p = 0.034). CONCLUSIONS: High intratumoral FAP expression was associated with worse survival, suggesting that intratumoral FAP expression represents malignant progression in patients with IHCC. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12876-023-03012-x.