Supplementary Material for: Anti-HER2 therapies in biliary tract cancers: A meta-analysis on disease location, HER2 status, and survival outcomes

Introduction
In recent years, the therapeutic scenario of metastatic biliary tract cancers (BTC) beyond first-line has profoundly changed owing to target therapies. HER2 represents a promising molecular target that is frequently altered in BTC. The present meta-analyses are aimed to describe the response rates and survival outcomes in patients with HER2-positive locally advanced/metastatic BTC treated with anti-HER2 therapies. Moreover, the study is intended to provide an update on the evolving therapeutic scenario of HER2 overexpressed BTC.

Methods
We performed a systematic review of the literature to identify clinical trials investigating any regimen comprising a HER2 targeted therapy for metastatic BTC, and we conducted three subsequent meta-analyses on second-line phase II trials. The first one was performed to compare the group of HER2 3+ versus the group of HER2 2+ BTC patients for objective response rate (ORR). The second one compared patients according to the tumor location (gallbladder carcinoma [GBC] or extrahepatic cholangiocarcinoma [eCCA] versus intrahepatic cholangiocarcinoma [iCCA]) for ORR. The third one evaluated the overall outcomes in terms of overall survival (OS) and progression-free survival (PFS).

Results
Patients with advanced BTC and HER2 3+ had better ORR compared to HER2 2+, with a 3.7-fold higher probability of experiencing objective responses (HR 3.70, 95% CI 1.34-10.25, p=0.0119). Likewise, patients with GBC or eCCA had a 2.74-fold higher probability of experiencing an objective response compared to patients with iCCA (HR 2.74, 95% CI 1.12-6.73, p=0.0275). The weighted pooled analysis of trials with anti-HER2 agents in second-line or beyond revealed a mPFS of 4.9 months (95% CI 4.2-5.6), while mOS was 10.8 months (95% CI 9.0-12.8).

Conclusions
Our meta-analyses have revealed improved efficacy in patients with HER2 3+ metastatic BTC and in patients with GBC or eCCA treated with anti-HER2 therapies, with a considerable mPFS and mOS in the overall population of the phase II trials analyzed. Further studies are paramount to confirm our preliminary results.