Evaluation of the serotonin pathway as a biomarker in cholangiocarcinoma.

Background: Cholangiocarcinomas (CCAs) are rare and aggressive malignant tumors of the biliary tract. Serotonin (5HT) has tumor-promoting effects in CCA while inhibition of 5HT synthesis can decrease tumor growth.

Methods: In this retrospective study, we evaluated the expression of 5HT and tryptophane hydroxylase-1 (TPH-1) in tumor specimens from patients treated with cisplatin plus gemcitabine (CisGem). We included consecutive patients ≥18 years, with locally advanced unresectable, recurrent, or metastatic CCA who were treated with CisGem and had available archival tumor tissue for immunohistochemistry. Formalin-fixed paraffin (FFPE) sections were stained for 5HT and TPH-1. Specimens were evaluated for neuroendocrine features and tumor-infiltrating lymphocytes (TILs). Serum 5HT was measured.

Results: We identified 23 patients fulfilling the inclusion criteria. 5HT expression was absent in almost all tumors examined. TPH-1 expression was neither associated with stage or primary tumor location nor predictive of response to CisGem. There was a trend for improved overall survival (OS) in patients whose tumors had high TPH-1 expression. The examined tumor specimens had no neuroendocrine features. Most sections had no TILs. There was a trend for worse OS in patients with high serum 5HT concentration.

Conclusions: Tumor TPH-1 expression was not predictive of response to treatment. There was a trend for improved long-term outcomes in patients with high tumor TPH expression and lower serum 5HT concentration.