Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 2 3 2018 02 17 82 86 EN Shahideh Amini Department of Clinical Pharmacy, School of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. Bita Shahrami Department of Clinical Pharmacy, School of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran. Besharat Rahimi Thoracic Research Center AND Division of Pulmonary and Critical Care, Department of Pulmonary Diseases, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Soheil Peiman Department of Internal Medicine, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. 2017 12 04 2017 12 26 Hypereosinophilia is defined as eosinophil count more than 1500 per microliter that can be associated with tissue and organ damage, regardless of the underlying cause. There are various categories of diseases that are able to cause eosinophilia. Solid tumor-associated hypereosinophilia is an unusual manifestation in patients with cancer. Cytokines namely granulocytes macrophages stimulating factor (GM-CSF), interleukin 3 (IL- 3), and interleukin 5 (IL-5) may play an important role in the pathogenesis of eosinophilia development. Here, we describe a 70-year-old man with metastatic adenocarcinoma of the lung presenting with fever, weight loss, shortness of breath, and severe hypereosinophilia. In patients with compatible clinical findings and associated risk factor(s), it is important to consider lung adenocarcinoma as a differential diagnosis in patients with unexplained eosinophilia and lung symptoms with associated risk factors. https://crcp.tums.ac.ir/index.php/crcp/article/view/153 https://crcp.tums.ac.ir/index.php/crcp/article/download/153/85