The 1940-1946 period consolidated a view of lung cancer as a heterogeneous disease with distinct presentations and progression patterns, reinforced by large clinical series, post-mortem analyses, and early diagnostic innovations such as sputum cytology, radiology, and bronchoscopic biopsy that supported timely diagnosis and differential diagnosis from masquerading diseases. Experimental and histogenetic work using animal models illuminated carcinogenesis pathways and histogenesis of induced pulmonary tumors, while surgical series began to reveal early evidence on treatment impact and prognosis, highlighting regional variations in thoracic tumor subtypes and localization. Historical Significance: Metastasis emerged as a core feature shaping staging, prognosis, and therapeutic concepts that persisted for decades, while the development of chemical carcinogenesis models in animals provided a foundational framework for mechanistic cancer studies and intervention testing. Foundational histogenetic studies and descriptions of benign lesions such as hamartomas underscored the importance of accurate classification and environmental or nutritional factors in cancer risk, setting a long-range research trajectory that integrated pathology, biology, and clinical management.