Pneumonitis

Pneumonitis is non-infectious inflammation of the lung parenchyma. Three cancer treatments cause it often enough to shape practice. Checkpoint inhibitors cause it in about 3 to 5 percent of people on single-agent anti-PD-1, more in lung cancer and after thoracic radiotherapy, and 5 to 10 percent with combinations; it is fatal in a small minority, which is out of proportion to its frequency among immune-related adverse events. Several antibody-drug conjugates, notably the deruxtecan family used in lung and breast cancer, carry interstitial lung disease and pneumonitis as a labelled risk requiring scheduled imaging. Radiotherapy to the chest causes radiation pneumonitis weeks to months after treatment, in the shape of the radiation field, and can be followed by fibrosis. The workup is the same whatever the cause: high-resolution CT of the chest, oxygen saturation at rest and on exertion, and exclusion of infection and of cancer progression, with bronchoscopy and lavage where it is safe. Management turns on grade: hold the drug and observe at grade 1, steroids and usually a hold at grade 2, high-dose steroids with admission and often permanent discontinuation at grade 3 or above. Because breathlessness in a lung cancer patient has many other causes, the practical rule is that a new or worse cough or breathlessness on one of these treatments is investigated urgently rather than attributed to the cancer.