pembrolizumab
Keytruda (pembrolizumab) is a PD-1 checkpoint inhibitor from Merck used across many cancers, including melanoma, lung, kidney, gastric, and triple-negative breast cancers, Hodgkin lymphoma, and MSI-H or dMMR tumours. By releasing the PD-1 brake on T cells, it restores immune attack on cancer, alone or with combinations.
This page is based on FDA prescribing information and the EMA medicine record for pembrolizumab, cross-checked with DailyMed and the National Cancer Institute dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
A tumour raises a molecular white flag that presses the PD-1 brake on attacking T cells, so the immune patrol stands down. Pembrolizumab covers the brake. The flag no longer works, the T cells stay switched on, and they hunt down cancer cells wherever they hide.
In simple terms
T cells are built to destroy abnormal cells, but many cancers protect themselves by displaying ligands PD-L1 and PD-L2 that bind the PD-1 off-switch on T cells. Pembrolizumab is a humanized antibody that blocks PD-1, so tumours can no longer deliver that off signal. Freed from suppression, T cells reactivate and attack cancer cells throughout the body, which is why the drug is useful across so many tumour types, including any solid tumour with MSI-H or dMMR biology.
In depth
Pembrolizumab is a humanized monoclonal immunoglobulin G4 antibody directed against the human cell surface receptor PD-1. Upon administration it binds PD-1, an inhibitory signalling receptor expressed on activated T cells, and blocks binding and activation by its ligands PD-L1, which is overexpressed on certain cancer cells, and PD-L2, which is primarily expressed on antigen-presenting cells. Because activated PD-1 negatively regulates T-cell activation and plays a key role in tumour evasion from host immunity, blocking the receptor restores T-cell-mediated immune responses against tumour cells. Selection for some indications uses PD-L1 expression or MSI-H/dMMR testing.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
How pembrolizumab, a humanized anti-PD-1 antibody, frees T cells across many tumour types including MSI-H/dMMR
- A tumour raises a molecular white flag that presses the PD-1 brake on attacking T cells, so the immune patrol stands down.
- Pembrolizumab is a humanized monoclonal immunoglobulin G4 antibody directed against the human cell surface receptor PD-1.
- Because activated PD-1 negatively regulates T-cell activation and plays a key role in tumour evasion from host immunity, blocking the receptor restores T-cell-mediated immune responses against tumour cells.
- Selection for some indications uses PD-L1 expression or MSI-H/dMMR testing.
Target: Programmed death-1 (PD-1) receptor
An inhibitory receptor on activated T cells that tumours exploit through its ligands PD-L1 and PD-L2 to escape immune attack; blocking PD-1 reactivates T-cell responses against cancer cells.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in United States
FDA- For the treatment of patients with unresectable or metastatic melanoma, and for the adjuvant treatment of adults and pediatric patients 12 years and older with Stage IIB, IIC, or III melanoma following complete resection
- In combination with pemetrexed and platinum chemotherapy, for the first-line treatment of patients with metastatic nonsquamous non-small cell lung cancer with no EGFR or ALK genomic tumor aberrations
- In combination with carboplatin and either paclitaxel or paclitaxel protein-bound, for the first-line treatment of patients with metastatic squamous non-small cell lung cancer
- As a single agent, for the first-line treatment of patients with non-small cell lung cancer expressing PD-L1 (Tumor Proportion Score of 1 percent or more) with no EGFR or ALK genomic tumor aberrations that is Stage III where patients are not candidates for surgical resection or definitive chemoradiation, or metastatic
- For the treatment of adult patients with relapsed or refractory classical Hodgkin lymphoma, and of pediatric patients with refractory classical Hodgkin lymphoma or disease that has relapsed after two or more lines of therapy
- For the treatment of adults and pediatric patients with unresectable or metastatic microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) solid tumors that have progressed following prior treatment and who have no satisfactory alternative treatment options
- For the treatment of patients with unresectable or metastatic MSI-H or dMMR colorectal cancer
- In combination with trastuzumab and fluoropyrimidine- and platinum-containing chemotherapy, for the first-line treatment of adults with locally advanced unresectable or metastatic HER2-positive gastric or gastroesophageal junction adenocarcinoma whose tumors express PD-L1 (CPS of 1 or more)
- In combination with axitinib or with lenvatinib, for the first-line treatment of adult patients with advanced renal cell carcinoma
- For the treatment of patients with high-risk early-stage triple-negative breast cancer in combination with chemotherapy as neoadjuvant treatment, then continued as a single agent as adjuvant treatment after surgery
- In combination with paclitaxel, with or without bevacizumab, for the treatment of adults with platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal carcinoma whose tumors express PD-L1 (CPS of 1 or more) and who have received one or two prior systemic treatment regimens
Approved uses in European Union
EMA- As monotherapy, for the treatment of adults and adolescents aged 12 years and older with advanced (unresectable or metastatic) melanoma
- As monotherapy, for the adjuvant treatment of adults and adolescents aged 12 years and older with Stage IIB, IIC, or Stage III melanoma and lymph node involvement who have undergone complete resection
- In combination with platinum-containing chemotherapy as neoadjuvant treatment, then continued as monotherapy as adjuvant treatment, for the treatment of resectable non-small cell lung carcinoma at high risk of recurrence in adults
- As monotherapy, for the first-line treatment of adults with metastatic non-small cell lung carcinoma whose tumours express PD-L1 with a tumour proportion score of 50 percent or more and have no EGFR or ALK positive tumour mutations
- In combination with pemetrexed and platinum chemotherapy, for the first-line treatment of adults with metastatic non-squamous non-small cell lung carcinoma whose tumours have no EGFR or ALK positive mutations
- As monotherapy, for the treatment of adults with locally advanced or metastatic non-small cell lung carcinoma whose tumours express PD-L1 with a tumour proportion score of 1 percent or more and who have received at least one prior chemotherapy regimen
Official sources
The statements on this page trace back to these records.
- Keytruda (pembrolizumab) — Summary of product characteristics and package leaflet, English version
European Medicines Agency
- DailyMed: KEYTRUDA (pembrolizumab) official US label
U.S. National Library of Medicine, DailyMed
- U.S. Food and Drug Administration: pembrolizumab prescribing information
U.S. Food and Drug Administration
- National Cancer Institute: pembrolizumab
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.