Case report: Hypereosinophilia in non-small cell lung cancer

Hypereosinophilia, as defined by the absolute eosinophil count ≥ 1,500 cells per microliter, can be a consequence of primary (clonal) hematologic disorders or secondary response to inflammation from allergens, parasitic infections, medications or cancer. Its evaluation requires comprehensive history and physical as well as laboratory studies to identify the underlying cause and assess for evidence of end-organ damage in concern for hypereosinophilia syndrome. Here, we report a rare case of paraneoplastic hypereosinophilia with an absolute eosinophil count exceeding 70,000 cells per microliter in the setting of a newly diagnosed metastatic non-small cell lung cancer. A 60-year-old Caucasian male smoker with past medical history of cerebrovascular accidents and heart failure with reduced ejection fraction presented with acute encephalopathy and later developed multi-system organ failure. Peripheral blood smear and other hematologic studies were not suggestive of clonal hematologic malignancy. Extensive infectious work-up of peripheral blood, lower respiratory tract and cerebrospinal fluid was negative. Review of recent medical record did not identify any potentially causative drugs. Diagnostic thoracentesis of the loculated pleural effusion showed poorly differentiated non-small cell lung cancer, which was deemed as the underlying etiology of his profound hypereosinophilia. His encephalopathy and other signs and symptoms of end organ damage were thought less likely to be directly driven by hypereosinophilia. Progressive critical illness unfortunately precluded disease-directed therapy and his family opted for comfort care to mitigate suffering. Our case report highlights paraneoplastic etiology as an important diagnostic consideration in a patient with unexplained hypereosinophilia. Review of the literature shows that hypereosinophilia in patients with non-small cell lung cancer and other solid malignancies correlates with rapid disease progression and poor prognosis, though the underlying mechanisms remain unclear. Interestingly, case reports of hypereosinophilia in non-small cell lung cancer suggest a male-biased incidence. Investigation of the role of eosinophils in modulating anti-tumor immunity and its sex difference is warranted.