"The doctor said the gastric cancer is already advanced and chemotherapy isn't working well—is there any other option?" This is the question many patients and families ask. As one of the most common digestive tract cancers, gastric cancer has a guarded prognosis, especially when locally advanced or metastatic. Immunotherapy has brought new hope; Keytruda (pembrolizumab), a PD-1 inhibitor, is a major advance in gastric cancer treatment.
Keytruda (pembrolizumab) is an immune checkpoint inhibitor—an anti–PD-1 monoclonal antibody. It works by "removing the tumor's disguise": gastric cancer cells use the PD-1/PD-L1 pathway to evade the immune system; Keytruda blocks this pathway so the body's immune cells can again find and destroy cancer cells. Unlike chemotherapy ("kill the enemy at great cost") or targeted therapy ("precise strike"), Keytruda "activates the body's own immunity against cancer," with less damage to normal cells and better tolerability.
Eligibility depends on stage, PD-L1 expression (CPS), HER2 status, and MSI status. Main groups:
• HER2-negative, locally advanced unresectable or metastatic gastric/gastroesophageal junction cancer, PD-L1 CPS≥5: Keytruda plus fluoropyrimidine and platinum (NCCN category 1). • HER2-negative, CPS≥1: Keytruda plus fluoropyrimidine and platinum is also an option (NCCN 2A). • HER2-positive, CPS≥1: Keytruda plus trastuzumab and fluoropyrimidine and platinum (NCCN category 1).
• After prior chemotherapy failure, locally advanced or metastatic gastric/GEJ cancer that is MSI-H (microsatellite instability–high)—about 5–20% of gastric cancers—responds well to Keytruda. • After chemotherapy failure, intolerance, or refusal of chemotherapy: Keytruda monotherapy may be considered after assessment (with PD-L1 or MSI).
• Hypersensitivity to Keytruda or any component: do not use. • Severe hepatic or renal impairment, active autoimmune disease, or severe infection: use with caution; doctor must weigh risks and benefits. • Pregnancy and breastfeeding: not recommended.
Data from KEYNOTE phase III trials and real-world experience.
• KEYNOTE-062 (first-line): In PD-L1 CPS≥1, Keytruda monotherapy ORR 57.1%, Keytruda plus chemo ORR 64.7% vs chemo 36.8%; Keytruda monotherapy median PFS 11.2 months, combination not reached vs chemo 6.6 months. • KEYNOTE-061 (second-line): In MSI-H, Keytruda median PFS 17.8 months vs paclitaxel 3.5 months, ORR 46.7% vs 16.7%. • KEYNOTE-059 (third-line and beyond): In MSI-H, Keytruda monotherapy ORR 57.1%; some patients had long-term disease control.
In eligible patients, Keytruda can control disease, reduce toxicity, and improve quality of life, including long-term control; individual response varies and must be assessed by the treating team.
Step 1—Before treatment: PD-L1 (CPS), MSI, and HER2 testing are essential to decide if and how to use Keytruda; also blood counts, liver and kidney function, thyroid function, ECG, chest and abdominal CT. Step 2—Treatment plan: Set by the doctor. Keytruda monotherapy 200 mg every 3 weeks IV; combination with chemotherapy or with trastuzumab plus chemotherapy depends on HER2 and fitness. Do not decide on your own. Step 3—During treatment: Monitor vital signs and allergic reactions during infusions; at home watch for rash, diarrhea, fever, fatigue, thyroid changes and report to the doctor; regular follow-up (e.g. every 6–9 weeks for first-line); do not stop or reduce dose without doctor approval; avoid unapproved supplements or herbs. Step 4—After treatment: Long-term follow-up (e.g. every 3 months in year 1, every 6 months in years 2–3, then yearly), including blood tests, imaging, and tumor markers; bring prior records for comparison.
Cost and insurance: Keytruda is on national reimbursement in many regions for advanced/metastatic gastric cancer when criteria are met; reimbursement rate varies (often about 50–80%); check with local insurance or hospital. Side effects: Most are grade 1–2 (rash, fatigue, diarrhea) and manageable; serious immune-related events (e.g. pneumonitis, myocarditis) are uncommon but require immediate stop and medical care. If Keytruda doesn't work: Options may include other PD-1/PD-L1 inhibitors, different chemotherapy, or targeted therapy; the doctor will tailor the next plan. Diet and activity: Light, digestible, adequate protein and vitamins; small frequent meals; gentle exercise (e.g. walking) 30 minutes, 3–4 times per week if able; avoid exhaustion.
Keytruda offers new hope for locally advanced or metastatic gastric cancer but is not for everyone; PD-L1, MSI, and HER2 testing define eligibility. Follow your doctor's plan for testing, monitoring, and follow-up to get the best outcome and quality of life. This guide is for information only and does not replace medical advice; treatment and follow-up must be decided by your doctor. We wish every patient precise care and recovery.
More CancerCura and care knowledge