Supplementary Material for: Mismatch repair deficiency in biliary tract cancer: prognostic implications and correlation with histology.

Introduction: Mismatch repair (MMR) deficiency represents a biomarker and therapeutic target in various neoplasms, but its role in biliary tract cancers (BTCs) remains misunderstood. Methods: MMR status was retrospectively assessed using immunohistochemistry in 163-BTCs patients. We identified MMR proficiency (pMMR)/deficiency (dMMR) according to the loss of MMR proteins (MLH-1, PMS-2, MSH-2, MSH-6). The primary objective of the study was to assess the incidence of dMMR in BTCs; the secondary purpose was to explore its association with prognosis and clinical features. Results: dMMR was recorded in 9 patients and it was strongly associated with mucinous histology (p<0.01). Regarding the prognostic effect, in 122-radically resected patients, disease-free-survival (DFS) resulted significantly shorter in dMMR-patients compared to pMMR-patients (10.7 vs 31.3 months, p = 0.025) and so did nodal status (48.2 vs 15.3 months in N0 vs N+) (p < 0.01). Moreover, dMMR confirmed its prognostic role in terms of DFS at multivariate analysis (p = 0.03), together with nodal status (p = 0.01) and resection margin (p = 0.03). In 103 M+ patients (encompassing 41 metastatic de novo and 62 recurred after surgery patients) there weren’t differences between dMMR and pMMR regarding survival analyses. Discussion/Conclusions: dMMR status is strongly correlated with mucinous histology and represents an independent prognostic factor in terms of disease-relapse in patients with resected BTC.