Abstract: The authors report a case of papillary thyroid carcinoma combined with primary pulmonary squamous cell carcinoma, which triggered a leukemoid reaction. The diagnostic and treatment process, as well as relevant auxiliary examination results, are described in detail, followed by a review and analysis based on related literature, which aims to enhance clinicians' understanding of leukemoid reactions, improve early diagnostic capabilities, alert the possibility of multiple primary cancers, and thereby avoid missed diagnoses and misdiagnoses in clinical practice.