Pembrolizumab (Keytruda) - Mechanism & Uses
Pembrolizumab is an immune checkpoint inhibitor used to treat various types of cancer. It works by reactivating the immune system to recognize and destroy tumor cells.
Things worth knowing about "Pembrolizumab"
Pembrolizumab is an immune checkpoint inhibitor used to treat various types of cancer. It works by reactivating the immune system to recognize and destroy tumor cells.
What is Pembrolizumab?
Pembrolizumab is a monoclonal antibody belonging to the class of drugs known as immune checkpoint inhibitors. It is marketed under the brand name Keytruda and manufactured by MSD (Merck Sharp & Dohme). Pembrolizumab has been approved by the European Medicines Agency (EMA) and the U.S. Food and Drug Administration (FDA) for a wide range of cancer types, making it one of the most broadly approved cancer immunotherapy drugs to date.
Mechanism of Action
Pembrolizumab works by targeting the PD-1 receptor (Programmed Death-1), a protein found on the surface of T-cells -- a key component of the immune system. Under normal conditions, the PD-1 pathway acts as a brake on the immune response, preventing it from becoming overactive. Cancer cells exploit this mechanism by expressing a protein called PD-L1, which binds to PD-1 and effectively shields them from immune detection.
By blocking the interaction between PD-1 and PD-L1, pembrolizumab releases this brake and allows T-cells to once again recognize and attack cancer cells.
Approved Indications
Pembrolizumab is approved for the treatment of numerous cancer types, including:
- Melanoma (advanced or metastatic)
- Non-small cell lung cancer (NSCLC)
- Head and neck squamous cell carcinoma
- Classical Hodgkin lymphoma
- Bladder cancer (urothelial carcinoma)
- Gastric and gastroesophageal junction adenocarcinoma
- Cervical cancer
- Colorectal cancer with microsatellite instability-high (MSI-H)
- Triple-negative breast cancer
- And additional solid tumors with specific molecular characteristics
Dosage and Administration
Pembrolizumab is administered as an intravenous (IV) infusion. The standard dosing schedules are:
- 200 mg every 3 weeks, or
- 400 mg every 6 weeks
The specific dose and duration of treatment depend on the cancer type, the overall health of the patient, and the response to therapy. Each infusion typically takes approximately 30 minutes and is given in an oncology clinic or hospital setting.
Side Effects
Because pembrolizumab enhances immune activity, it can cause immune-related adverse events (irAEs) that may affect almost any organ system. Common side effects include:
- Fatigue and general weakness
- Skin reactions (rash, itching)
- Diarrhea and colitis (inflammation of the bowel)
- Lung inflammation (pneumonitis)
- Thyroid disorders (hypothyroidism or hyperthyroidism)
- Liver inflammation (hepatitis)
- Adrenal insufficiency
Serious immune-related reactions are uncommon but can be life-threatening and require prompt medical management, often with corticosteroids.
Biomarkers and Patient Selection
Not all patients respond equally to pembrolizumab. Key biomarkers used to predict treatment response include:
- PD-L1 expression: Higher levels of PD-L1 in tumor tissue are often associated with a better response.
- Microsatellite instability-high (MSI-H): Tumors with this characteristic tend to respond particularly well.
- Tumor mutational burden (TMB-H): Tumors with a high number of mutations may also show improved response rates.
Contraindications and Precautions
Pembrolizumab should not be used in patients with known hypersensitivity to the active substance. Special caution is advised in patients with:
- Active autoimmune diseases
- Severe organ dysfunction
- Pregnancy or breastfeeding, as embryotoxic effects cannot be excluded
References
- European Medicines Agency (EMA): Keytruda (Pembrolizumab) - Product Information and Approval Status. Available at: https://www.ema.europa.eu
- Brahmer, J.R. et al. - Safety and Activity of Anti-PD-1 Antibody in Patients with Advanced Cancer. New England Journal of Medicine, 2012; 366:2455-2465.
- Robert, C. et al. - Pembrolizumab versus Ipilimumab in Advanced Melanoma. New England Journal of Medicine, 2015; 372:2521-2532.
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