A case of lung adenocarcinoma expressing carbonic anhydrase IX and cluster of differentiation 10 antigen combined with renal clear cell carcinoma

Few reports exist on dual primary lung and kidney tumors. Lung adenocarcinoma and renal clear-cell carcinoma are usually distinguished based on histological morphology and characteristic immunohistochemistry. This study describes a patient with concurrent lung adenocarcinoma and clear cell renal cell carcinoma, notable for their shared expression of both carbonic anhydrase IX (CA9) and cluster of differentiation 10 (CD10) markers, a phenomenon that has remained unreported in existing literature. We made a correct diagnosis based on histological morphology and immunohistochemical results, discussed the significance of CA9 and CD10 expression in lung adenocarcinoma, and provided insights for differential diagnosis, intending to offer pathologists relevant insights for diagnosing multiple primary malignant neoplasms.