What causes immunotherapy side effects?

The immune system normally uses control signals to limit attacks on the body's own cells. Immunotherapy changes some of those controls so immune cells can recognise and attack cancer more effectively. In some people, that increased activity creates inflammation in organs such as the skin, bowel, lungs, liver, thyroid, or pituitary gland.

Symptoms may start during treatment or after a dose has finished. They can include a new rash, diarrhoea, cough, breathlessness, yellowing of the skin, severe tiredness, headache, or changes in thirst and urination. The symptom alone does not show how serious the inflammation is, so prompt reporting matters.

Tell your oncology team about new or worsening symptoms, including changes that seem mild. Give the date they began, how often they occur, and whether they interfere with eating, drinking, sleep, or daily activity. The team may arrange blood tests, scans, stool tests, hormone checks, or breathing assessment to identify the affected organ.

Treatment may involve pausing immunotherapy and using medicines that reduce harmful inflammation. Do not take leftover steroids or anti-diarrhoeal medicines without guidance, because the right approach depends on the organ involved and the severity.

Seek urgent help for difficulty breathing, chest pain, severe diarrhoea, blood in stool, marked weakness, confusion, fainting, seizures, rapidly worsening headache, or inability to keep fluids down. These can signal inflammation requiring immediate assessment.

Which symptoms should I report immediately? Which organs does my treatment affect most often? Should my next dose be delayed? What tests will distinguish an immune reaction from infection or cancer symptoms?