Trastuzumab Plus Gemcitabine-Cisplatin for Treatment-Naïve Human Epidermal Growth Factor Receptor 2–Positive Biliary Tract Adenocarcinoma: A Multicenter, Open-Label, Phase II Study (TAB)

PURPOSE Human epidermal growth factor receptor 2 (HER2) overexpression is seen in 4%-16% of biliary tract cancers (BTCs). We aimed to evaluate the clinical activity of gemcitabine-cisplatin (GC) plus anti-HER2 antibody trastuzumab as initial treatment in HER2-positive BTCs. METHODS This study was an investigator-initiated, open-label, single-arm, multi-institutional, phase II trial in adult patients with HER2-positive (defined as immunohistochemistry [IHC] 3+ or IHC 2+ and fluorescent in situ hybridization–positive), treatment-naïve BTCs. The primary end point of the study was 6-month progression-free survival (PFS). Next-generation sequencing was performed on tissue samples to evaluate mutational status. RESULTS From March 2020 to August 2022, of the 876 screened patients, 118 (13.4%) were found to have HER2-positive status, of whom 90 were enrolled in the study. Most patients had GBC (n = 96; 96%) with two or more sites of metastatic disease (n = 70; 78%). With a median follow-up of 17.3 (95% CI, 15.22 to 19.32) months, 72 patients had disease progression with a median PFS of 7 (95% CI, 6.2 to 7.8) months. The diagnosis to event 6-month PFS rate was 75.6% (95% CI, 66.6 to 84.6). A complete or partial response was seen in 50 (55.5%) patients and 22 (24.4%) patients had stable disease as the best response to treatment, for an overall disease control rate of 80%. The presence of isolated TP53 mutations was associated with inferior PFS compared with other mutations (TERT promoter, HER2, PIK3CA, etc) or no detected mutations (6.51 v 12.02 v 10.58 months; P < .001). CONCLUSION The combination of GC and trastuzumab achieved its primary end point of improving PFS compared with historical data in the treatment-naïve HER2-positive BTC. Evaluating additional mutations such as TP53 and PIK3CA along with HER2 testing may help to preferentially select patients for anti-HER2 therapy in the future (Clinical Trial Registry India number: CTRI/2019/11/021955).