Table of Contents
Introduction
Pembrolizumab, marketed under the brand name Keytruda, is an advanced immunotherapy drug that has revolutionized cancer treatment. It works by helping the immune system to more effectively recognize and destroy cancer cells. Pembrolizumab has improved survival outcomes for many cancer patients, but it is extremely important to understand the side effects of pembrolizumab before starting therapy.
This guide explains common, serious, and rare Pembrolizumab Side Effects, as well as management tips, monitoring recommendations, and safety precautions that every patient should be aware of.
How Pembrolizumab Works in the Body
Pembrolizumab is a monoclonal antibody that targets the PD-1 receptor (programmed death-1) on immune cells called T-lymphocytes. Normally, PD-1 acts as a “brake,” preventing T-cells from attacking healthy cells. Cancer cells take advantage of this mechanism by expressing PD-L1, a ligand that binds to PD-1 and disables the immune attack.
By blocking PD-1, pembrolizumab releases this brake, allowing immune cells to attack tumor cells.
However, this immune activation can cause the immune system to mistakenly attack normal organs—which can lead to immune-related side effects.
Common Pembrolizumab Side Effects
These are the side effects most often reported in clinical trials and real-world use. They may occur in the first few weeks of treatment but are usually mild to moderate.
1. Fatigue
One of the most common pembrolizumab side effects is fatigue. Patients may feel unusually tired even after rest. Staying hydrated, maintaining a balanced diet, and taking short naps can help manage this symptom.
2. Skin Reactions
Rashes, itching, and skin dryness are frequent immune-related reactions. In some cases, redness or mild peeling occurs. Use gentle moisturizers and avoid harsh soaps. Inform your oncologist if the rash worsens or covers a large area.
3. Nausea and Loss of Appetite
Pembrolizumab may cause mild gastrointestinal effects, including nausea or appetite changes. Eating smaller, frequent meals and avoiding spicy foods can reduce discomfort.
4. Cough or Shortness of Breath
Lung inflammation (pneumonitis) can cause cough or breathing issues. This requires immediate medical attention, as untreated pneumonitis can become severe.
5. Diarrhea
Inflammation in the intestines (colitis) can lead to loose stools or abdominal cramps. Mild diarrhea can be managed with hydration, but persistent or bloody stools need urgent evaluation.
Serious Pembrolizumab Side Effects (Immune-Mediated Reactions)
Because pembrolizumab boosts immune function, sometimes the immune system attacks normal organs. These reactions are known as immune-mediated adverse events (irAEs) and can affect nearly any organ system.
1. Lung (Pneumonitis)
- Symptoms: Persistent cough, chest pain, or shortness of breath
- Action: Stop treatment temporarily and use corticosteroids if inflammation is confirmed.
2. Liver (Hepatitis)
- Symptoms: Yellowing of skin or eyes (jaundice), dark urine, or elevated liver enzymes
- Action: Regular liver function tests are essential during therapy.
3. Endocrine Glands
Pembrolizumab can affect hormone-producing glands such as:
- Thyroid (hypo- or hyperthyroidism)
- Adrenal glands
- Pituitary gland (hypophysitis)
Symptoms include fatigue, weight changes, mood swings, or temperature intolerance. Hormone replacement therapy may be needed.
4. Colon (Colitis)
- Symptoms: Diarrhea, abdominal pain, or blood in stools
- Action: High-dose corticosteroids and supportive care if severe.
5. Kidney (Nephritis)
- Symptoms: Decreased urine output, swelling in legs or feet, increased creatinine levels
- Action: Regular kidney tests during treatment cycles.
Rare and Long-Term Pembrolizumab Side Effects
Though uncommon, some pembrolizumab side effects can appear months after stopping treatment.
1. Neurological Effects
- Symptoms: Muscle weakness, numbness, tingling, or difficulty walking
- These could indicate inflammation of nerves (neuropathy) or the brain (encephalitis).
2. Heart Inflammation (Myocarditis)
Pembrolizumab may cause inflammation of heart tissue, resulting in chest pain or irregular heartbeat. Immediate evaluation by a cardiologist is essential.
3. Pancreatitis
Inflammation of the pancreas can lead to severe abdominal pain and vomiting. This side effect is very rare but requires urgent medical care.
4. Eye Disorders
Uveitis (eye inflammation) may cause redness or blurred vision. Prompt ophthalmologic examination is needed to prevent vision loss.
Managing Pembrolizumab Side Effects
Early detection and management are vital for safety and continued treatment success.
Tips for Patients
- Report new or unusual symptoms immediately.
- Keep a symptom diary during treatment cycles.
- Maintain hydration and eat a nutrient-rich diet.
- Use gentle skincare routines to prevent irritation.
- Avoid self-medicating without consulting your oncologist.
For Healthcare Providers
- Conduct baseline liver, kidney, and thyroid tests before starting pembrolizumab.
- Schedule routine blood tests during therapy.
- Educate patients about warning signs of immune reactions.
Who Should Avoid Pembrolizumab?
Pembrolizumab may not be suitable for everyone. The drug should be used with caution or avoided in:
- Patients with autoimmune diseases such as lupus or rheumatoid arthritis.
- Those who have had organ transplants (risk of rejection).
- Pregnant or breastfeeding women (risk to fetus or infant).
Always consult an oncologist before starting pembrolizumab therapy.
Lifestyle Support During Pembrolizumab Therapy
Supportive care plays a key role in minimizing pembrolizumab side effects.
- Nutrition: Include antioxidants and high-protein foods to boost recovery.
- Exercise: Gentle activities like yoga or walking help maintain energy levels.
- Mental Health: Emotional stress can worsen fatigue; consider counseling or meditation.
- Sleep: Aim for 7–8 hours per night to support immune balance.
Monitoring and Follow-Up
Your oncology team will schedule follow-ups to monitor for pembrolizumab side effects even after treatment ends. Long-term observation ensures early detection of delayed immune responses.
Tests typically include:
- Complete blood count (CBC)
- Liver and kidney function tests
- Thyroid function panel
- Chest imaging for lung inflammation
Key Takeaways
- Pembrolizumab activates your immune system to fight cancer but can also cause immune-related side effects.
- Most side effects are manageable when detected early.
- Never ignore new symptoms — timely medical evaluation can prevent severe complications.
- Maintaining a healthy lifestyle and staying in touch with your healthcare team can greatly reduce risk.
Conclusion
Understanding the pembrolizumab side effects helps patients and caregivers make informed treatment decisions. Pembrolizumab offers hope in many cancers, but proactive management of its side effects ensures a safer and more effective treatment journey.
Always remember: report early, stay informed, and work closely with your oncologist to achieve the best possible outcome.