Lung Adenocarcinoma and Peripheral Blood Eosinophilia

There are many causes of peripheral blood eosinophilia (PBE), including allergic, infectious, rheumatic, and hematologic disorders. Solid tumor cancers, such as lung cancer, can also cause PBE, and although rare, being diagnosed with PBE in this way is associated with a worse prognosis than for lung cancer patients without PBE. Additionally, some cancer patients develop PBE when receiving treatment with immune checkpoint inhibitors (ICIs). When PBE is caused in this way, the outcome varies. On the one hand, there are reports of severe adverse events, while on the other, ICIs-induced PBE may be a predictive biomarker of better outcomes. This article reports on the case of a 66-year-old male patient with metastatic lung adenocarcinoma presenting with paraneoplastic hypereosinophilia aggravated by pembrolizumab.