Zanidatamab plus chemotherapy as first-line treatment for patients with HER2-positive advanced gastro-oesophageal adenocarcinoma: primary results of a multicentre, single-arm, phase 2 study

Abstract

Summary Background

Zanidatamab, a dual human epidermal growth factor receptor 2 (HER2)-targeted bispecific antibody, previously demonstrated encouraging antitumour activity and a manageable safety profile in patients with treatment-refractory HER2-expressing gastro-oesophageal adenocarcinoma. Here, we evaluated the antitumour activity and safety of zanidatamab plus chemotherapy in first-line HER2-positive advanced gastro-oesophageal adenocarcinoma.

Methods

This phase 2 trial enrolled patients in Canada, South Korea, and the USA who were aged 18 years and older with untreated, metastatic, or advanced HER2-positive gastro-oesophageal adenocarcinoma (HER2 IHC 3+ or 2+ by local or central assessment [part 1]; HER2 IHC 3+ or 2+ with FISH+ by central assessment [part 2]). Eligible patients, with an Eastern Cooperative Oncology Group performance status of 0 or 1 received zanidatamab intravenously plus standard chemotherapy (CAPOX [capecitabine plus oxaliplatin], FP [5-fluorouracil [5-FU] plus cisplatin], or modified FOLFOX6 [mFOLFOX6; leucovorin, 5-FU, and oxaliplatin]). In our study, part 1 aimed to characterise the safety and tolerability of zanidatamab and find the recommended dose when administered with combination chemotherapy and part 2 aimed to evaluate the antitumour activity of zanidatamab administered with combination chemotherapy in patients receiving first-line treatment for HER2-expressing advanced gastro-oesophageal adenocarcinoma. Two dosing schemes for zanidatamab were used in this study: a weight-based regimen and a two-tiered flat dosing regimen. In the CAPOX and FP groups, patients received either 30 mg/kg zanidatamab or 1800 mg or 2400 mg (patients weighing <70 kg and ≥70 kg, respectively) every 3 weeks. In the CAPOX group, patients also received 1000 mg/m 2 capecitabine orally twice daily on days 1–14 every 3 weeks, plus 130 mg/m 2 oxaliplatin intravenously every 3 weeks. In the FP cohort, patients also received 80 mg/m 2 cisplatin intravenously every 3 weeks, plus 800 mg/m 2 5-FU per day continuous intravenous infusion on days 1–5 every 3 weeks. In the mFOLFOX6 group, patients received either 20 mg/kg zanidatamab or 1200 mg or 1600 mg for patients weighing under 70 kg or 70 kg and above, respectively, every 2 weeks, plus 400 mg/m 2 intravenous leucovorin every 2 weeks, 85 mg/m 2 intravenous oxaliplatin every 2 weeks, and 1200 mg/m 2 5-FU per day as a continuous intravenous infusion for 48 h every 2 weeks. mFOLFOX6–1 included the administration of a 400 mg/m 2 5-FU intravenous bolus on days 1 and 15; mFOLFOX6–2 omitted this 5-FU bolus. The primary endpoints of part 1 were safety and tolerability, which included frequencies of dose-limiting toxicities and dose reductions of zanidatamab and chemotherapy. The primary antitumour activity endpoint of part 2 was confirmed objective response rate assessed in the response-evaluable analysis set. Secondary endpoints included objective response rate, duration of response, disease control rate, clinical benefit rate, progression-free survival, and overall survival. Safety outcomes were assessed in all treated patients. We report the results from an interim analysis. This trial is registered at ClinicalTrials.gov ( NCT03929666) and is complete for enrolment.

Findings

Between Aug 29, 2019, and Feb 18, 2022, 46 patients were enrolled (39 [85%] were male; seven [15%] were female; 28 [61%] were white, 17 [37%] were Asian, and 43 [93%] were not Hispanic or Latino). Median follow-up was 47·9 months (IQR 39·2–53·7); eight (17%) patients were on treatment and 19 (41%) were in survival follow-up. The confirmed objective response rate was 76·2% (95% CI 60·5–87·9) with a median duration of response of 18·7 months (95% CI 10·4–44·1). The median progression-free survival was 12·5 months (95% CI 8·2–21·8) and median overall survival was 36·5 months (23·6–not estimable). The disease control rate was 88·1% (95% CI 74·4–96·0) and clinical benefit rate was 78·6% (95% CI 63·2–89·7). In part 1, there were no dose-limiting toxicities in six patients treated with zanidatamab plus CAPOX. One (50%) of two patients treated with zanidatamab plus FP had dose-limiting toxicities of diarrhoea and acute kidney injury (both grade 3). Two dose-limiting toxicities of diarrhoea (both grade 3) occurred in 2 (15%) of 13 patients receiving 5-FU 400 mg/m 2 bolus on day 1 and 15 as part of the zanidatamab plus mFOLFOX6–1 regimen. 30 (65%) patients had treatment-related grade 3 or 4 adverse events. The most common treatment-related grade 3 or 4 adverse events were diarrhoea (18 [39%]; five [24%] in the 21 patients after implementing mandatory antidiarrhoeal prophylaxis) and hypokalaemia (ten [22%]). Six (13%) patients discontinued zanidatamab due to adverse events. No treatment-related deaths occurred.

Interpretation

Zanidatamab plus chemotherapy as first-line treatment of HER2-positive advanced gastro-oesophageal adenocarcinoma demonstrated clinically meaningful and durable antitumour activity, with a manageable safety profile.

Funding

Jazz Pharmaceuticals, Zymeworks.