Fig. 1.

Representative microscopic images of solid-pattern adenocarcinoma (a, b), papillary-pattern adenocarcinoma (c, d), adenocarcinoma in situ (AIS) (e, f), and INV-2 tumor (g, h). Solid-pattern adenocarcinoma shows sheet-like growth of tumor cells, with destroyed elastic fibers of the remnant alveolus around the tumor nest (arrow) (a, b). Papillary-pattern adenocarcinoma shows secondary-to-tertiary papillae in which glandular cells grow along with the fibrovascular core independent of the surrounding alveolar elastic fibers (arrow) (c, d). AIS shows the proliferation of tumor cells in a monolayer fashion along the surface of the alveolar walls (e). Elastica van Gieson staining reveals the preserved alveolar elastic fibers (arrow) (f). In INV-2 adenocarcinoma, tumor cells grow in a monolayer fashion along the surface of alveolar walls, and active fibroblasts (arrowhead) are present in the thickened alveolar interstitial tissue (g). Alveolar elastic fibers are observed as a single thin line or as a dense aggregation (arrow) along the tumor cells (h). Original magnification: x100 in all pictures. Hematoxylin-eosin (a, c, e, g) and Elastica van Gieson (b, d, f, h) staining.