What is pembrolizumab (Keytruda) and is it used for Lung Cancer

Pembrolizumab (Keytruda) for Lung Cancer

What Is Pembrolizumab?

Pembrolizumab is an immunotherapy drug — a type of cancer treatment that works differently than traditional chemotherapy. Instead of directly attacking cancer cells, pembrolizumab helps your immune system recognize and fight cancer cells on its own.

Here's how it works:

The Basic Mechanism: Cancer cells have a clever trick — they hide from your immune system by displaying a protein called PD-L1 on their surface. This protein acts like a "do not attack" signal. Pembrolizumab blocks this signal by binding to a receptor called PD-1 on immune cells. By removing this "invisibility cloak," pembrolizumab allows your immune system's T-cells to see and destroy the cancer cells.

Pembrolizumab for Lung Cancer

Yes, pembrolizumab is FDA-approved and widely used for non-small cell lung cancer (NSCLC). According to the NCCN Guidelines for Non-Small Cell Lung Cancer, pembrolizumab is a Category 1 preferred option — the highest recommendation level — for treating advanced lung cancer.

How It's Used

First-Line Treatment (Initial Therapy): According to NCCN Guidelines, pembrolizumab can be used as:

1. Single-agent monotherapy (pembrolizumab alone) for patients with:

   • Advanced NSCLC with PD-L1 expression of 50% or more
   • No actionable driver mutations (like EGFR or ALK mutations)
   • The KEYNOTE-024 trial showed median overall survival of 26.3 months with pembrolizumab monotherapy versus 13.4 months with chemotherapy alone

2. Combination therapy (pembrolizumab + chemotherapy) for patients with:

   • Advanced NSCLC regardless of PD-L1 levels
   • The KEYNOTE-189 trial showed one-year overall survival of 69.2% with pembrolizumab plus chemotherapy versus 49.4% with chemotherapy alone

Subsequent Therapy (After Initial Treatment): Pembrolizumab is also recommended for patients whose cancer has progressed after other treatments, particularly those with PD-L1 expression of 1% or more.

The PD-L1 Test: A Key Decision Point

Before starting pembrolizumab, your doctor will order a PD-L1 immunohistochemistry (IHC) test on your tumor tissue. This test measures what percentage of your cancer cells display the PD-L1 protein:

• 50% or more PD-L1 expression = Strong candidate for pembrolizumab monotherapy
• 1-49% PD-L1 expression = May benefit from pembrolizumab + chemotherapy
• Less than 1% PD-L1 expression = Pembrolizumab + chemotherapy still recommended

According to NCCN Guidelines, "The NCCN NSCLC Panel recommends IHC testing for PD-L1 expression (category 1) before first-line treatment in all patients with metastatic NSCLC."

Real-World Outcomes

The clinical trial data is encouraging:

• 5-year overall survival with pembrolizumab monotherapy: approximately 29.6% for patients with PD-L1 levels of 50% or more (compared to about 6% with chemotherapy alone)
• Response rates (tumors shrinking): 44.8% with pembrolizumab versus 27.8% with chemotherapy
• Fewer severe side effects than chemotherapy: 31.2% grade 3-5 adverse events with pembrolizumab versus 53.3% with chemotherapy

Important Considerations

Immune-Related Side Effects: Because pembrolizumab activates your immune system, it can cause immune-mediated adverse events (side effects caused by immune activation). These may include:

• Pneumonitis (lung inflammation)
• Myocarditis (heart inflammation)
• Skin reactions
• Gastrointestinal issues
• Thyroid problems

According to NCCN Guidelines, if you experience severe immune-related side effects, your doctor may need to pause or discontinue treatment and may prescribe high-dose corticosteroids to manage the reaction.

Not Suitable If You Have:

• EGFR mutations or ALK rearrangements (targeted therapies are preferred first-line)
• Contraindications to PD-1/PD-L1 inhibitors (your doctor will assess this)

Questions to Ask Your Oncologist

1. What is my PD-L1 expression level, and what does that mean for my treatment options?
2. Am I a candidate for pembrolizumab monotherapy, or would combination therapy with chemotherapy be better for me?
3. What immune-related side effects should I watch for, and how will we monitor for them?
4. How will we measure if pembrolizumab is working? How often will I have scans or blood tests?
5. What other treatment options do I have, and how does pembrolizumab compare to them?

---

This information is for educational purposes only. Always consult your healthcare team for personalized medical advice and decisions.