Keytruda side effects: what to know

Keytruda helps immune cells respond to cancer, but that immune activity can sometimes affect healthy tissues. Problems may involve the skin, thyroid, bowel, lungs, liver, kidneys, nerves, or hormone-producing glands. Symptoms can begin during treatment or after an infusion has ended.

The same symptom can have more than one cause. For example, tiredness may relate to cancer, anaemia, sleep, another medicine, or immune inflammation. A hoarse voice can have several explanations and needs assessment rather than a self-diagnosis.

Keep a simple record of when a symptom began, how it changes, medicines taken, bowel movements, temperature, and breathing. Tell the oncology team about new symptoms before taking over-the-counter treatment. The team may arrange blood tests, scans, hormone checks, or other assessments.

Treatment might continue, pause, or change according to the finding. Management can include fluids, replacement hormones, steroids, or specialist care. Do not conceal symptoms because they seem mild or because an earlier scan was reassuring.

Call the cancer team urgently for worsening cough or breathlessness, persistent diarrhoea, blood in stool, severe abdominal pain, yellow skin or eyes, very little urine, severe headache, confusion, new weakness, vision changes, or a spreading blistering rash. Seek emergency help for severe breathing difficulty, fainting, seizure, or swelling of the face or throat.

Ask which symptoms need a same-day call, whether you need a home thermometer or symptom diary, which medicines to avoid, how treatment will be paused or treated if inflammation is found, and whom to contact outside clinic hours.