Can Keytruda (pembrolizumab) cause blood clots?
Keytruda can be associated with blood clots in some patients. Immune checkpoint inhibitors, including pembrolizumab, have been linked to blood clotting events such as deep vein thrombosis (DVT) and pulmonary embolism (PE) in post-marketing reports and clinical experience.
What kinds of blood clots might happen?
Reported clot types include:
- Deep vein thrombosis (clots in the leg or other deep veins)
- Pulmonary embolism (a clot that travels to the lungs)
- Other thrombotic events reported with immune-related therapies
The exact risk varies by patient and cancer type, but the key point is that clotting events are a known possible complication.
How would you know if a clot is happening? (symptoms to watch)
Blood clot symptoms depend on where the clot forms:
- DVT: swelling, pain, warmth, or redness in one leg (or arm)
- PE: shortness of breath, chest pain (often worse with breathing), coughing (sometimes with blood), fast heart rate, lightheadedness
These can be medical emergencies. If symptoms suggest a clot, patients should seek urgent care.
Why might Keytruda increase clot risk?
Several mechanisms are possible with cancer plus immunotherapy, including:
- The underlying cancer itself raising clot risk
- Inflammation and immune activation from treatment
- Therapy-related effects that can affect the body’s balance of clotting and bleeding
Cancer patients already have an elevated baseline risk for clotting, so Keytruda’s contribution may be hard to separate from the malignancy and other risk factors.
Who is at higher risk for clots while on Keytruda?
Risk is often higher in people with one or more of the following:
- Prior history of DVT/PE
- Certain cancer types (and advanced disease)
- Recent surgery, immobility, or hospitalization
- Active smoking
- Estrogen-containing medications (where relevant)
- Other clotting risk factors such as thrombophilia or major comorbidities
What should clinicians do if a clot occurs?
If a blood clot occurs, clinicians typically evaluate promptly and treat according to standard clot management (often anticoagulation), while also reassessing whether to hold or continue immunotherapy based on the severity of the event and overall risk.
When to contact a doctor right away
Contact urgent care or emergency services immediately if there are symptoms consistent with DVT or PE, especially:
- New one-sided leg swelling or pain
- Sudden shortness of breath or chest pain
If you tell me the patient’s cancer type and current symptoms (and whether they have a history of clots), I can help you map the situation to what clinicians usually consider urgent.