Trastuzumab Deruxtecan in Human Epidermal Growth Factor Receptor 2-Expressing Biliary Tract Cancer (HERB; NCCH1805): A Multicenter, Single-Arm, Phase II Trial.

PURPOSE: Treatment options for patients with unresectable or recurrent biliary tract cancer (BTC) who progress on a gemcitabine-containing regimen are limited. In addition, the significance of anti-human epidermal growth factor receptor 2 (HER2) therapy in HER2-expressing BTC has not been sufficiently investigated. METHODS: In this phase II trial, participants from five institutions in Japan were enrolled. Eligible patients had pathologically confirmed unresectable or recurrent BTC with centrally confirmed HER2-positive (immunohistochemistry [IHC]3+ or IHC2+ and in situ hybridization [ISH]+) or HER2-low (IHC2+ and ISH-, IHC1+, and IHC0 and ISH+) and were refractory or intolerant to a gemcitabine-containing regimen. The patients received 5.4 mg/kg trastuzumab deruxtecan (T-DXd) once every 3 weeks until disease progression or unacceptable toxicity. The primary end point was the confirmed objective response rate (ORR) in HER2-positive BTC by an independent central review (threshold ORR, 15%; expected ORR, 40%). RESULTS: A total of 32 patients were enrolled and treated. Among these patients, 22 with HER2-positive disease comprised the primary efficacy population and had a confirmed ORR of 36.4% (90% CI, 19.6 to 56.1; P = .01), meeting the primary end point. Eight with HER2-low disease comprised the exploratory population and had a confirmed ORR of 12.5%. The most common ≥grade 3 treatment-related adverse events were anemia (53.1%) and neutropenia (31.3%). Eight patients (25.0%) had interstitial lung disease (ILD), including two grade 5 events. CONCLUSION: T-DXd showed promising activity in patients with HER2-positive BTC and a signal of efficacy in patients with HER2-low BTC. Although the safety profile was generally manageable, ILD requires careful monitoring and early intervention.