In this article
On March 19, 2025, the Food and Drug Administration officially approved pembrolizumab (Keytruda, Merck) to be used along with trastuzumab and chemotherapy that includes fluoropyrimidine and platinum for the first treatment of adults with locally advanced, inoperable, or metastatic HER2-positive gastric or gastroesophageal junction (GEJ) adenocarcinoma that shows PD-L1 expression (CPS ≥1). Pembrolizumab was granted accelerated approval for this indication on May 5, 2021, based on an interim analysis of the trial detailed below.
The effectiveness was tested in KEYNOTE-811 (NCT03615326), a big study with 698 patients who had HER2-positive advanced gastric or gastroesophageal junction adenocarcinoma and had not been treated before for their metastatic disease. They took part in a randomized, double-blind trial that compared the treatment to a placebo. Out of these 698 patients, 594 (85%) had tumors that showed PD-L1 expression at a CPS ≥1, as checked by the PD-L1 IHC 22C3 pharmDx kit. Patients were randomly divided into equal groups to receive either pembrolizumab 200 mg or a placebo, along with trastuzumab and either fluorouracil plus cisplatin or capecitabine plus oxaliplatin. The main results looked at in patients were how long they lived without their disease getting worse (progression-free survival, or PFS) as checked by an independent review, and how long they lived overall (overall survival, or OS). The additional results included the overall response rate (ORR) and how long the response lasted (duration of response or DOR). People who received pembrolizumab along with trastuzumab and chemotherapy had a noticeable improvement in overall survival (OS) and progression-free survival (PFS) compared to those who got a placebo with trastuzumab and chemotherapy. In patients with tumors exhibiting PDL1 CPS≥1, the median progression-free survival (PFS) was 10.9 months (95% CI: 8.5, 12.5) in the pembrolizumab group and 7.3 months (95% CI: 6.8, 8.4) in the placebo group (Hazard ratio [HR] 0.72 [95% CI: 0.60, 0.87]). The median overall survival (OS) was 20.1 months (95% confidence interval [CI]: 17.9, 22.9) and 15.7 months (95% CI: 13.5, 18.5) in the respective groups, with a hazard ratio (HR) of 0.79 (95% CI: 0.66, 0.95). The overall response rate (ORR) was 73% (95% confidence interval: 68, 78) and 58% (95% confidence interval: 53, 64), whereas the median duration of response (DOR) was 11.3 months (95% confidence interval: 9.9, 13.7) and 9.6 months (95% confidence interval: 7.1, 11.2). The adverse reaction profile reported in patients administered pembrolizumab aligned with the established safety profile of pembrolizumab. The advised dosage of pembrolizumab is 200 mg every three weeks or 400 mg every six weeks, administered alongside trastuzumab and chemotherapy.
How CancerFax Helps
CancerFax is a specialist cancer access and patient-navigation platform. We help patients and families understand their options, organise medical records, coordinate hospital communication, and support cross-border treatment planning where appropriate.
We help collect and organise reports, scans, pathology, biomarker results, and treatment history for structured case review.
We communicate with hospitals or trial teams to assess whether a case may be suitable for further screening.
We support appointment coordination, document submission, translation, and direct communication with international departments.
For international patients, we help with practical coordination — travel planning, hospital admission guidance, and local support.
If this option is not suitable, we help explore other relevant treatments, clinical trials, or advanced care pathways.
From inquiry through to follow-up, our coordinators provide a single point of contact for the family.
CancerFax does not guarantee treatment access, eligibility, or clinical outcome. Our role is to help patients access accurate information, structured review, and appropriate specialist pathways.
About Sai Sree
✓ Reviewed for medical accuracy by the CancerFax review panel.
Medical Disclaimer
This article is for educational purposes only and should not replace medical advice, diagnosis, or treatment from a qualified oncology specialist. Every patient's case is different. Treatment decisions should always be made after a review of complete medical records by the treating medical team.
Treatment availability, eligibility, timelines, and access can change. Any clinical trial participation depends on detailed review and approval by the trial hospital or investigator.