Gastric cancer, also known as stomach cancer, remains a serious global health problem. While surgery, chemotherapy, and targeted therapies continue to play a central role, outcomes for advanced gastric cancer were historically limited. Over the past decade—and especially by 2025—immunotherapy has become an important part of treatment for selected patients, improving survival and offering durable benefit for some.
Understanding the immunotherapy success rate for gastric cancer can be challenging. Immunotherapy does not work the same way as chemotherapy, and its benefits depend strongly on tumor biology, biomarkers, and treatment setting. This article explains how immunotherapy is used in gastric cancer today, what clinical studies show, who benefits most, and what patients should realistically expect in 2025.
Read About Stomach Cancer on OncoDaily
How Immunotherapy Works in Gastric Cancer
Immunotherapy drugs used in gastric cancer are mainly immune checkpoint inhibitors, such as pembrolizumab and nivolumab. These drugs block immune “brakes” like PD-1 or PD-L1, which cancer cells use to hide from the immune system. By releasing these brakes, immunotherapy allows immune cells to recognize and attack cancer more effectively (Fuchs et al., 2018).
In gastric cancer, immunotherapy is most commonly used in advanced or metastatic disease, either alone in selected patients or, increasingly, in combination with chemotherapy as first-line treatment (Janjigian et al., 2021).
What “Success Rate” Means for Patients
When patients ask about the immunotherapy success rate for gastric cancer, doctors consider more than just tumor shrinkage. Success may include:
- Tumor response (shrinkage seen on scans)
- Disease control (cancer stops growing)
- Longer overall survival
- Durable benefit lasting months or years
- Improved quality of life compared with chemotherapy alone
Because immunotherapy works through the immune system, responses may take time and are not seen in all patients.
What Clinical Trials Show About Success Rates
Later-Line Immunotherapy
Early trials established the role of immunotherapy after chemotherapy. In the ATTRACTION-2 study, nivolumab improved overall survival compared with placebo in heavily pretreated patients, with an overall response rate of about 11% and long-lasting responses in some individuals (Kang et al., 2017).
Similarly, the KEYNOTE-059 trial showed that pembrolizumab produced responses in approximately 15% of previously treated patients, with higher response rates in tumors expressing PD-L1 (Fuchs et al., 2018).
First-Line Immunotherapy Plus Chemotherapy
By 2025, the biggest impact of immunotherapy in gastric cancer has come from first-line combination therapy. The CheckMate 649 trial demonstrated that nivolumab plus chemotherapy significantly improved overall survival compared with chemotherapy alone, especially in patients with PD-L1 combined positive score (CPS) ≥5 (Janjigian et al., 2021).
In these studies, response rates exceeded 40%, compared with roughly 25–30% with chemotherapy alone. Importantly, survival improvements were seen even when tumors did not shrink dramatically, highlighting the immune-mediated benefit.
HER2-Positive Gastric Cancer
For patients with HER2-positive gastric cancer, the addition of pembrolizumab to trastuzumab and chemotherapy further improved outcomes. In KEYNOTE-811, response rates reached over 70%, leading to regulatory approvals and changing first-line standards of care (Janjigian et al., 2023).
The MATTERHORN Trial
The MATTERHORN trial is one of the most important studies influencing the immunotherapy success rate for gastric cancer in 2025. Unlike earlier trials focused on advanced disease, MATTERHORN evaluated immunotherapy in resectable stage II–III gastric and gastroesophageal junction cancer, where the goal is cure.
In this Phase III study, durvalumab was added to standard perioperative FLOT chemotherapy given before and after surgery. The trial showed a significantly higher pathologic complete response rate, meaning more patients had no remaining cancer at the time of surgery compared with chemotherapy alone (Janjigian et al., 2024). Durvalumab also improved event-free survival, reducing the risk of recurrence after surgery.
While overall survival data are still maturing, these findings suggest that immunotherapy can increase the chance of long-term remission when used earlier in treatment. Benefits were seen across patient groups, with greater effects in PD-L1–positive tumors.
For patients diagnosed in 2025, MATTERHORN shows that immunotherapy success in gastric cancer is no longer limited to metastatic disease and may play an important role in curative-intent treatment strategies.
Read About MATTERHORN Trial on OncoDaily
Who Benefits Most From Immunotherapy in 2025
Not all patients benefit equally from immunotherapy. Key factors that influence success include:
PD-L1 Expression: Patients with higher PD-L1 CPS scores generally have better outcomes with immunotherapy, particularly when combined with chemotherapy (Janjigian et al., 2021).
MSI-H / dMMR Tumors: A small percentage of gastric cancers are microsatellite instability-high (MSI-H). These tumors are highly responsive to immunotherapy, with response rates often exceeding 50% and very durable benefit (Le et al., 2017).
Treatment Setting: Immunotherapy works best when used earlier in the disease course, particularly in first-line combination regimens rather than as a last resort.
Real-World Outcomes and Durability
Real-world data now support what clinical trials showed: although only a subset of patients respond, those who do may experience long-term disease control. Some patients remain progression-free for years, which was rarely seen with chemotherapy alone.
Equally important, many patients report better tolerability and preserved quality of life compared with prolonged chemotherapy, especially after the initial treatment period.
Side Effects: What Patients Should Expect
Immunotherapy is generally better tolerated than chemotherapy, but side effects can occur. These are caused by immune activation and may include fatigue, skin rash, diarrhea, thyroid changes, or inflammation of organs such as the lungs or liver. Most side effects are manageable when detected early, and oncology teams monitor patients closely throughout treatment (Postow et al., 2018).
What Patients Should Know in 2025
By 2025, immunotherapy is no longer experimental in gastric cancer—it is part of standard care for many patients. However, it is not a one-size-fits-all treatment. Biomarker testing, including PD-L1 and MSI status, is essential to guide decisions. Combination approaches are now preferred in most first-line settings, and clinical trials continue to explore new combinations and earlier use.
Patients should feel empowered to ask their oncologist how the immunotherapy success rate for gastric cancer applies to their specific diagnosis and what factors may influence their chance of benefit.
Key Takeaway for Patients
Immunotherapy has meaningfully improved outcomes for gastric cancer, particularly when combined with chemotherapy or used in biomarker-selected patients. While it is not a cure for most, it offers longer survival, durable responses, and improved quality of life for many. In 2025, immunotherapy represents one of the most important advances in gastric cancer treatment, and understanding who benefits most is key to making informed care decisions.
You Can Watch More on OncoDaily Youtube TV
Written by Armen Gevorgyan, MD