Paraneoplastic Leukemoid Reaction in Lung Adenocarcinoma With Multi-lineage Granulocytic Abnormalities and Eosinophilic Pleural Effusion.

This report describes a rare and lethal phenotype of paraneoplastic leukemoid reaction (PLR) in lung adenocarcinoma, defined by a triad of multi-lineage myeloid proliferation, marked eosinophilic malignant pleural effusion, and progressive lymphopenia. The patient presented with a hyper-aggressive clinical course, culminating in a fatal outcome within 12 days, suggesting an underlying multi-cytokine storm. Clinically, this triad serves as a critical alert for distinguishing PLR from infection and underscores the importance of early bone marrow evaluation for rapid diagnosis. This case highlights the urgent need for mechanistic studies of multi-cytokine-driven PLR.