SFTPC and neoplasm: In R+ N1w/w mice, bronchiolar airways were rarely invaded by SPC+ tumor cells whereas in R+ N1f/f mice, SPC+ cells which were located within the bronchiolar lining formed epithelial carcinoma in situ lesions protruding from the bronchiolar wall (arrow 4) and budding into the bronchiolar lumen (arrow 5) (Figure 2E).