Zanidatamab and Tislelizumab: A Gastric Cancer Breakthrough

The therapeutic landscape for advanced HER2-positive gastroesophageal cancer is evolving rapidly. In addition, researchers published findings from the highly anticipated Phase 3 HERIZON-GEA-01 clinical trial. This study compared zanidatamab plus chemotherapy, with or without tislelizumab, against standard trastuzumab plus chemotherapy. Consequently, oncologists have access to highly robust clinical efficacy data.

The Efficacy of Zanidatamab in HER2-Positive Gastroesophageal Cancer

Specifically, the study evaluated patients with untreated, advanced HER2-positive gastroesophageal adenocarcinoma. Investigators randomized participants to receive either a zanidatamab triplet, a zanidatamab doublet, or standard trastuzumab plus chemotherapy. Furthermore, the median follow-up period spanned 25.9 months. Consequently, the investigators could measure key long-term survival statistics accurately.

The progression-free survival results showed dramatic clinical improvements. Both zanidatamab-containing arms achieved a median progression-free survival of 12.4 months. Conversely, the trastuzumab control arm only achieved a median progression-free survival of 8.1 months. This represents a significant risk reduction for disease progression. Therefore, the bispecific antibody showed clear superiority over traditional trastuzumab.

Survival Benefits and Safety Parameters

Importantly, the overall survival data also favored the novel combinations. The zanidatamab-tislelizumab-chemotherapy triplet reached an unprecedented median overall survival of 26.4 months. Meanwhile, the trastuzumab-chemotherapy control arm demonstrated a median overall survival of 19.2 months. Additionally, this survival benefit remained consistent regardless of the patient’s baseline PD-L1 expression level.

However, safety profiles required careful monitoring during the trial. Grade 3 or higher adverse events occurred more frequently in the triplet therapy arm. Specifically, patients reported elevated rates of diarrhea, hypokalemia, and anemia. Therefore, clinical teams must balance the profound efficacy benefits with proactive symptom management strategies.

Frequently Asked Questions

Q1: What is the primary difference between zanidatamab and trastuzumab?

Zanidatamab is a bispecific antibody that targets two distinct domains of the HER2 receptor simultaneously. Conversely, trastuzumab only targets a single HER2 domain, making zanidatamab a more potent therapeutic option.

Q2: How did the addition of tislelizumab affect survival outcomes?

Specifically, the addition of tislelizumab to zanidatamab and chemotherapy prolonged the median overall survival to 26.4 months. Consequently, this combination represents a significant survival advantage over trastuzumab plus chemotherapy.

Q3: What were the most common severe adverse events in the zanidatamab triplet arm?

The most common Grade 3 or higher adverse events included diarrhea, hypokalemia, and anemia. Therefore, clinical teams should monitor patients closely to manage these toxicities effectively.

References

1. Shitara K et al. Zanidatamab with and without Tislelizumab in HER2-Positive Gastroesophageal Cancer. N Engl J Med. 2026 May 28. doi: 10.1056/NEJMoa2517729. PMID: 42202319.
2. AJMC. HERIZON-GEA-01 Results Indicate Potential 1L Use of Zanidatamab for Gastroesophageal Adenocarcinoma. Published online January 7, 2026.
3. OncLive. Zanidatamab Plus Chemo ± Tislelizumab Improves Survival in HER2+ Gastroesophageal Adenocarcinoma. Published online May 27, 2026.