B80-5-05 Paraneoplastic Eosinophilia in Cavitary Squamous Cell Lung Carcinoma: A Rare Presentation

Abstract Introduction Lung cancer is frequently associated with paraneoplastic syndromes; however, paraneoplastic eosinophilia remains a rare occurrence. We present a case of cavitary squamous cell carcinoma (SCC) of the lung manifesting as marked peripheral eosinophilia. Case Presentation An 83-year-old male with dementia, benign prostatic hyperplasia, and a significant smoking history was admitted for progressive peripheral eosinophilia. Imaging revealed multiple bilateral cavitary pulmonary lesions. Extensive workup for infectious and autoimmune etiologies was unrevealing. Bronchoalveolar lavage and transbronchial biopsy confirmed moderately differentiated SCC with cavitation (Image 1). The patient was subsequently referred for oncologic evaluation and outpatient management. Discussion Squamous cell carcinoma, a subtype of non-small cell lung cancer (NSCLC), remains a leading cause of cancer-related mortality worldwide. Approximately 10% of lung cancer patients develop paraneoplastic syndromes, which can precede or signal tumor recurrence (Kanaji et al., 2014). Although eosinophilia is commonly associated with allergic, parasitic, or drug-related conditions, it may also represent a paraneoplastic phenomenon (Dinc et al., 2022). Paraneoplastic eosinophilia has been reported across lung cancer subtypes but remains rare in SCC. In this case, progressive eosinophilia prompted further investigation that revealed cavitary SCC. The proposed mechanism involves tumor overproduction of cytokines such as GM-CSF, IL-3, and IL-5, which stimulates eosinophil proliferation (Zalewska et al., 2021). Decline in eosinophil counts following tumor resection supports a tumor-derived source. Eosinophilia in NSCLC has been linked to poor prognosis, and rapid disease progression (Alhamwe et al., 2024; Lo et al., 2012). In our patient, the cavitary lesions initially suggested infectious etiologies (e.g., aspergillosis, tuberculosis) emphasizing the importance of including malignancy in the differential diagnosis. Cavitation, commonly seen in SCC, is associated with more aggressive disease and worse outcomes (Huang Y, 2024). Recognizing unexplained eosinophilia as a potential early paraneoplastic sign may aid in the timely diagnosis of underlying malignancy. Conclusion Peripheral eosinophilia is an uncommon but clinically significant paraneoplastic manifestation of lung SCC. In this case, progressive eosinophilia led to the diagnosis of cavitary SCC, underscoring the need to consider malignancy in patients with unexplained eosinophilia. Its presence may also indicate a poor prognosis (Venkatesan et al., 2015; Kwon et al., 2024). Image 1: Imaging and laboratory findings This abstract is funded by: None