Trastuzumab plus FOLFOX for HER2-positive biliary tract cancer refractory to gemcitabine and cisplatin: a multi-institutional phase 2 trial of the Korean Cancer Study Group (KCSG-HB19-14)

Background: HER2 overexpression or amplification, which is present in 15% of all cases of biliary tract cancer, has been identified as a druggable molecular target by genomic profiling. In the phase 3 ABC-06 trial, the folinic acid, fluorouracil, and oxaliplatin (FOLFOX) regimen showed a survival benefit compared with active symptom control as second-line therapy for biliary tract cancer. We aimed to evaluate the clinical activity of FOLFOX plus anti-HER2 antibody trastuzumab as a second-line or third-line treatment for HER2-positive biliary tract cancer. Methods: This study was an investigator-initiated, open-label, non-randomised, single-arm, multi institutional, phase 2 trial in participants aged 19 years or older with HER2-positive (defined as immunohistochemistry 3+ or immunohistochemistry 2+ and in-situ hybridisation positive or ERBB2 gene copy number ≥6·0 by next-generation sequencing) biliary tract cancer (intrahepatic cholangiocarcinoma, extrahepatic cholangiocarcinoma, and gallbladder cancer) who progressed on chemotherapy containing gemcitabine and cisplatin (with one or two previous chemotherapy lines permitted). In cycle one, patients received intravenous trastuzumab-pkrb at 6 mg/kg on day 1, and FOLFOX (consisting of intravenous oxaliplatin [85 mg/m2], intravenous leucovorin [200 mg/m2], and fluorouracil [400 mg/m2 bolus] all on day 1, and fluorouracil [2400 mg/m2 infusion] on days 1-2. In cycle two onwards, participants were administered intravenous trastuzumab-pkrb at 4 mg/kg and FOLFOX, every 2 weeks, until unacceptable toxic effects or disease progression. The primary endpoint of the study was objective response rate based on RECIST version 1.1, assessed in the participants who completed at least one study cycle. The response rate threshold for a positive objective response rate was 25%. This trial is registered with ClinicalTrials.gov (NCT04722133) and is ongoing. Findings: 34 participants were enrolled between June 26, 2020, and Sept 1, 2021. At the time of data cutoff on May 1, 2022, median ...