Biologic Downstaging Observed With a Pulmonary Collision Tumor.

Collision tumors are a rare entity in which 2 distinct neoplastic cellular populations invade each other and coalesce to form a single focal lesion. This case report describes a pulmonary collision tumor emerging from the rapid progression of 2 large-cell carcinoma lesions of the lung, including 1 nodule with clear cell features and another with basaloid features. The collision of these 2 histologically rare nodules resulted in the biologic downstaging of disease. This report provides unique insights into the biology of pulmonary collision tumors and its implications for diagnostic staging and therapeutic management.