Immunotherapy drugs have been hailed as a breakthrough in cancer treatment, offering new hope to patients who are out of treatment options. But as their use grows, doctors are finding that they pose serious risks, which arise from the very thing that makes them effective. An unleashed immune system can attack healthy, vital organs: notably the bowel, the liver and the lungs, but also the kidneys, the adrenal and pituitary glands, the pancreas and, in rare cases, the heart.

Also, some doctors believe immunotherapy is causing a new type of acute-onset diabetes. In cancer clinics around the world, and in drug trials, myriad other side effects are showing up. Studies are finding that severe reactions occur nearly 20 percent of the time with certain drugs, and in more than half of patients when some drugs are used in combination.

Another recent paper found that 30 percent of patients experienced “interesting, rare or unexpected side effects,” with a quarter of the reactions described as severe, life-threatening or requiring hospitalisation.

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