Can you tell me how large portion of lung tumors are cancers?

Majority are. benign lesions of lung such as the inflammatory lesions not that common. Rather malignant lesions that are primary of lung are the small cell and non small cell -squamous/adenoCa's. Metastatic tumors are derived from many glandular organs including GI tract, breast, These malignant lesions probably occur in 80%+ of cases.