Short answer: Keytruda (pembrolizumab) shares a common set of immune-related side effects with other immune checkpoint inhibitors, but the frequency and patterns of those effects can differ depending on the target (PD-1 vs PD-L1 vs CTLA-4), whether drugs are used alone or in combination, and the cancer type being treated.
Key points to know
- All of these drugs can unleash the immune system, so side effects are often immune-related (irAEs). The most frequent irAEs are generally mild and include fatigue, skin rash or itching, diarrhea, nausea, and decreased appetite.
- Endocrine effects are common across these drugs (thyroid dysfunction, sometimes hypophysitis with CTLA-4 inhibitors). Some endocrinopathies may require lifelong hormone replacement.
- Serious irAEs (grade 3–4) can involve any organ but most commonly:
- Skin and mucous membranes
- Colon (colitis/diarrhea)
- Liver (hepatitis)
- Lungs (pneumonitis)
- Endocrine glands (e.g., thyroid, pituitary)
- Kidneys (nephritis)
How Keytruda’s side effects compare by class
- PD-1 inhibitors (Keytruda, nivolumab, cemiplimab)
- Similar overall safety profiles.
- Common irAEs: fatigue, rash/itching, diarrhea, nausea, decreased appetite.
- Endocrine issues (thyroid problems) are relatively common.
- Pneumonitis and hepatitis can occur but are less frequent than with CTLA-4 inhibitors.
- In many settings, grade 3–4 irAEs occur in a minority of patients.
- PD-L1 inhibitors (atezolizumab, durvalumab, avelumab)
- Very similar pattern to PD-1 inhibitors.
- Some trials have suggested slightly different frequencies for certain irAEs (e.g., thyroid events), but overall the safety profile is broadly comparable to PD-1 inhibitors.
- Severe irAEs are uncommon but can occur.
- CTLA-4 inhibitors (ipilimumab)
- Tend to have a higher rate and earlier onset of irAEs, and more GI toxicity (colitis/diarrhea) and hypophysitis.
- Hepatitis and skin reactions can be more common than with PD-1/PD-L1 inhibitors.
- Overall, higher risk of serious irAEs compared with PD-1/PD-L1 inhibitors when used alone.
- Combination therapy (e.g., pembrolizumab + ipilimumab)
- IrAEs are more frequent and often more severe than with either agent alone.
- Requires closer monitoring and more aggressive management if irAEs occur.
Practical reminders
- The exact frequency and types of side effects can vary by cancer type, treatment setting (monotherapy vs combination), and dose/schedule. Check the specific drug label and your treatment plan for the most accurate information.
- If you notice symptoms such as new or worsening shortness of breath, persistent cough, chest pain, severe diarrhea or stomach pain, severe jaundice, dark urine, severe abdominal pain, severe headache with vision changes, severe rash or swelling, or extreme fatigue, contact your healthcare provider promptly. Some irAEs can be serious and require treatment with steroids or other therapies.
If you tell me which cancer type and whether Keytruda is being used alone or with another drug, I can summarize the typical side-effect patterns seen in that specific context and point to the most relevant guidance from dosing and labeling.