A first-line triplet regimen consisting of pembrolizumab, biosimilar trastuzumab (Herzuma), and chemotherapy is effective in patients with HER2-positive advanced gastric cancer, according to the results of a phase Ib/II study.
In recent years, there has been a growing body of evidence to suggest that the immune system contributes to the therapeutic effects of monoclonal antibodies (eg, biosimilar trastuzumab) in treating solid tumors. The PANTHERA trial is designed to evaluate the potential of first-line immunotherapy plus chemotherapy combined with biosimilar trastuzumab.
Sun Young Rha, MD, PhD, chief of medical oncology, Yonsei University College of medicine (Seoul, South Korea), and colleagues sampled 43 patients who were treated with pembrolizumab (200 mg IV, day 1), biosimilar trastuzumab (6 mg/kg, day 1), capecitabine (100 mg/m2 bid, day 1 to day 14), and cisplatin (80 mg/m2, day 1 every 3 weeks). Patients were followed for a median of 18 months.
The primary endpoint of the phase II evaluation was overall response rate (ORR), measured in accordance with the RECIST 1.1 guidelines. Among the secondary endpoints were progression-free survival (PFS), overall survival (OS), duration of response, and safety.
Results of the study were presented at the American Society of Clinical Oncology (ASCO) Annual Meeting (May 29-31, 2020).
Dr Rha and colleagues found a significant tumor shrinkage in 95.3% of patients. The ORR in the patient population was 76.7%, including a 16.3% complete response rate and a 60.5% partial response rate. They also noted that PD-L1 status at diagnosis did not significantly impact OS.
Additionally, researchers reported that the median PFS was 8.6 months (95% CI, 7.2-16.4) and the median OS was 19.3 months (95% CI, 16.5 to not achieved). The median duration of response was 10.8 months (95% CI, 7.17 to not achieved).
No new safety signals were observed, researchers added. The most common hematologic adverse events were a decreased neutrophil count (46.5%) and anemia (32.6%).
“Enabling access to first immunotherapy plus chemotherapy combination with biosimilar trastuzumab in the first-line setting will make a real difference to patients,” said Dr Rha in her presentation. “With the costs of oncology treatments being so burdensome, the availability of biosimilar trastuzumab could reduce the overall cost by combination treatment with innovative new drugs and chemotherapy.”—Zachary Bessette