Keytruda (pembrolizumab)

Keytruda® is an immunotherapy that is a monoclonal antibody. Antibodies are a normal part of the immune system that attach to antigens (such as germs) to mark them for destruction by the immune system. Monoclonal antibodies are created in a laboratory to attach to specific antigens on the surface of cancer cells. Pembrolizumab targets the PD-1 receptor and blocks the interaction with the proteins which bind to the receptor, PD-L1 and PD-L2. Some cancer cells affect the PD-1 pathway. When this pathway is affected by the cancer cells, the cancer can grow and spread without being kept in check by the T-cells and the immune system. By blocking the PD-1 pathway, pembrolizumab can help the body’s T-cells and immune system fight the cancer.1,2

Treatment option for NSCLC and SCLC

Pembrolizumab is approved for multiple first-line treatment options for for patients with certain forms of advanced non-small cell lung cancer. It can be used along with certain chemotherapy medications as initial treatment for metastatic (has spread to other parts of the body) nonsquamous non-small cell lung cancer (NSCLC) with no abnormal EGFR or ALK gene. As well as first-line treatment in combination with certain chemotherapy medications for metastatic squamous NSCLC.4 It can also be used as a single medication for certain forms of advanced or metastatic NSCLC. Pembrolizumab is used to treat other types of cancer, such as some melanoma cancers and some squamous cell carcinoma cancers.1,2

Additionally, pembrolizumab is approved for the treatment of metastatic small cell lung cancer (SCLC) in those with cancer progression after, or while taking, platinum-based chemotherapy and at least one other form of treatment.

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Pembrolizumab is also approved for the treatment of solid tumor cancers with certain biomarkers, including tumors that are considered tumor mutational burden-high (TMB-H), microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR).1

Receiving pembrolizumab

Pembrolizumab is given as an infusion that is administered through an IV (intravenous) line. Patients may be given medications before the infusion to reduce the chance of allergic reactions to pembrolizumab. The dosage of pembrolizumab is determined based on the type of cancer.2

Side effects of pembrolizumab

Pembrolizumab may cause side effects, and in some cases, these side effects can be severe. Any side effects should be reported to a health care professional. Side effects experienced in greater than approximately 30 percent of patients recieving pembrolizumab include low red blood cells (anemia), fatigue, hyperglycemia (high levels of sugar in the blood), hyponatremia (a decreased level of sodium in the blood), hypoalbuminemia (a decreased level of albumin in the blood), itching, cough, and nausea.

Less common side effects experienced in approximately 10-29 percent of patients receiving Keytruda include rash, decreased appetite, hypertriglyceridemia (an increased level of fatty acids in the blood), constipation, diarrhea, joint pain (arthralgia), pain in arms and legs, shortness of breath, swelling, headache, vomiting, chills, muscle pain (myalgia), insomnia (difficulty sleeping), abdominal pain, back pain, fever, vitiligo (a skin disorder with patchy loss of color), dizziness, and upper respiratory tract infection.

Pembrolizumab can cause the severe side effect of an immune-mediated reaction. This can affect the bowels, liver, skin, nerves and the endocrine system. Patients will be monitored for symptoms of this reaction (diarrhea, rash, and neuropathy) and blood work may be checked for elevated liver enzymes and thyroid function.2,3

This is not an exhaustive list of all potential side effects of pembrolizumab. Talk to your healthcare provider or pharmacist for further information.


Patients receiving pembrolizumab should talk to their doctor about any other medications (prescription and over-the-counter), herbal remedies, and any supplements they are taking, as well as any other health conditions.

Patients who are pregnant or may become pregnant during treatment should discuss their condition with their doctor before starting pembrolizumab, as it may be hazardous to the fetus. Women who could become pregnant should use birth control while receiving pembrolizumab and for at least 4 months after the last dose (patients should discuss appropriate birth control methods with their doctor). It is not known whether pembrolizumab passes into breast milk, and women should not breastfeed while receiving pembrolizumab and for 4 months following the last dose. Patients should talk to their doctor if they have any questions, or if they have questions regarding their pembrolizumab regimen.2

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Written by: Emily Downward | Last reviewed: January 2021.