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 IHC3+ 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.