Allergic bronchopulmonary aspergillosis presumably unmasked by PD-1 inhibition

Programmed cell death-1 (PD-1) inhibitors stimulate immune recognition of tumour cells in cancer patients, but have significant autoimmune side effects including pneumonitis. We report the case of a patient with asthma and mild eosinophilia who developed unusual pulmonary side effect of bronchiectasis, severe eosinophilia (absolute eosinophil count: 3200 c/mm³) and elevated IgE levels (7050 IU/mL; normal: <164 IU/mL) 4 months into therapy with the PD-1 inhibitor pembrolizumab. Aspergillus fumigatus IgG was elevated at 15.60 U/mL (normal: <12.01 U/mL). He responded to therapy with corticosteroids and voriconazole and was able to resume pembrolizumab thereafter with good clinical response.