Libtayo (cemiplimab) is a cancer immunotherapy drug approved to treat three types of cancer: cutaneous squamous cell carcinoma (a common skin cancer), basal cell carcinoma, and non-small cell lung cancer. It works by helping your immune system recognize and attack cancer cells that would otherwise evade detection. Libtayo is given as an intravenous infusion every three weeks.
How Libtayo Works
Cancer cells can hide from your immune system by displaying a protein on their surface that tells immune cells to stand down. Libtayo is a type of drug called a PD-1 inhibitor. It blocks the receptor on immune cells (called T cells) that cancer exploits to avoid being attacked. Once that “off switch” is blocked, your T cells can recognize tumor cells as threats and mount an immune response against them.
This approach, known as immune checkpoint therapy, doesn’t kill cancer cells directly the way chemotherapy does. Instead, it removes the brakes on your existing immune system and lets it do the work. That distinction matters because immune responses can be durable, sometimes continuing to suppress cancer growth long after treatment ends.
Cutaneous Squamous Cell Carcinoma
Libtayo was first approved for cutaneous squamous cell carcinoma (CSCC), a skin cancer that develops in the outer layer of skin. Most CSCC cases are caught early and removed surgically, but a small percentage become locally advanced (growing deep into surrounding tissue) or metastatic (spreading to distant parts of the body). Libtayo is approved for adults with metastatic or locally advanced CSCC who aren’t candidates for curative surgery or radiation.
In the pivotal clinical trial (EMPOWER-CSCC-1), about half of patients with metastatic CSCC saw their tumors shrink meaningfully, with 20% achieving a complete response, meaning no detectable cancer remained. For locally advanced CSCC, the overall response rate was 45%, with 13% achieving complete responses. These are notable numbers for a cancer that previously had no approved systemic treatment.
Libtayo also carries an approval for adjuvant use, meaning it can be given after surgery and radiation to patients whose CSCC has a high risk of coming back. This preventive approach aims to eliminate microscopic cancer cells that may have survived initial treatment.
Basal Cell Carcinoma
Basal cell carcinoma (BCC) is the most common type of skin cancer, and the vast majority of cases are treated successfully with surgery. But in rare cases, BCC becomes locally advanced or spreads to other parts of the body, making surgery insufficient. The standard first-line drug treatment for advanced BCC targets a specific growth pathway (the hedgehog pathway), but not all patients respond to it, and some can’t tolerate it.
Libtayo was approved in February 2021 for adults with locally advanced or metastatic BCC who have already tried a hedgehog pathway inhibitor or for whom that drug isn’t appropriate. For locally advanced cases, patients also need to have been deemed ineligible for curative surgery or radiation. This makes Libtayo a second-line option for a cancer that historically had very few treatment alternatives once first-line therapy failed.
Non-Small Cell Lung Cancer
Non-small cell lung cancer (NSCLC) accounts for roughly 85% of all lung cancers, and Libtayo is approved for two distinct roles in treating it. Both apply only to patients whose tumors don’t carry certain genetic mutations (EGFR, ALK, or ROS1 changes), since cancers with those mutations respond better to targeted therapies.
For patients whose tumors have high levels of a protein called PD-L1 (specifically, a Tumor Proportion Score of 50% or higher on an FDA-approved test), Libtayo can be used alone as a first-line treatment. High PD-L1 levels suggest the cancer is actively using that immune-evasion trick, making it a strong candidate for checkpoint blockade.
For patients with lower PD-L1 levels, or when a doctor determines combination therapy is more appropriate, Libtayo can be given alongside platinum-based chemotherapy as a first-line treatment. In both scenarios, the cancer must be locally advanced and not treatable with surgery or definitive chemoradiation, or it must be metastatic.
What Treatment Looks Like
Libtayo is given as an intravenous infusion at a flat dose of 350 mg. Each infusion takes about 30 minutes, and treatments are scheduled every three weeks. You’ll receive infusions at a clinic or infusion center, and treatment continues for as long as it’s working and you’re tolerating it. For the adjuvant skin cancer indication, there’s typically a defined course of treatment rather than an open-ended schedule.
Before and during treatment, your care team will run regular blood tests to check liver function, kidney function, and thyroid hormone levels. These tests help catch immune-related side effects early, since the drug’s mechanism of revving up your immune system can sometimes cause it to attack healthy tissues.
Common Side Effects
Because Libtayo activates the immune system broadly, side effects often reflect immune activity beyond the tumor. The most common issues patients experience include fatigue, rash, and musculoskeletal pain. Thyroid problems are particularly frequent: about 6% of patients in clinical trials developed an underactive thyroid (hypothyroidism), which typically requires thyroid hormone replacement but is manageable.
Immune-Related Risks
The more serious concern with any PD-1 inhibitor, including Libtayo, is immune-mediated adverse reactions. These occur when the unleashed immune system attacks healthy organs. While most are uncommon, they can affect nearly any part of the body.
- Lungs: Inflammation of the lungs (pneumonitis) occurred in about 2.4% of patients in trials.
- Liver: Immune-mediated hepatitis affected about 2.1% of patients, occasionally severe.
- Skin: Serious skin reactions occurred in 1.7% of patients, ranging from rashes to rare but dangerous conditions like blistering.
- Thyroid and other glands: Beyond common hypothyroidism, rarer hormonal disruptions include adrenal insufficiency, pituitary gland inflammation, and new-onset type 1 diabetes (0.7%).
- Colon: Immune-mediated colitis, causing diarrhea and abdominal pain, affected about 0.9% of patients.
- Kidneys: Nephritis occurred in 0.6% of patients.
Rarer but serious reactions can involve the heart (myocarditis), the nervous system (including conditions resembling Guillain-Barré syndrome), and the eyes (inflammation that can affect vision). Most immune-mediated side effects are reversible when caught early, which is why regular monitoring blood work is a standard part of treatment. If a serious reaction develops, treatment is paused or stopped, and the inflammation is typically treated with corticosteroids.