156 Chapter 12 In pulmonary adenocarcinoma, elastin staining can be used to demonstrate invasion in several ways. The most obvious are pleural and vascular invasion. Also, in preexisting disease the elastin pattern can be helpful. The elastin pattern in seemingly papillary structures, which could be either true papillary or pseudopapillary because of iatrogenic collapse, requires more explanation. Pleural invasion Recognition of the normal pleural elastin layer is used for staging. In small adenocarcinomas, elastin staining plays a role in determining the presence or absence of pleural invasion, defined as cancer cells infiltrating beyond the outer elastic layer or beyond the outer elastic layer and onto the visceral pleural surface17. Tumours ≤30 mm with pleural invasion are upstaged to pT2a (Figure 3). Figure 3. A,B, Overview (A) and detail (B) of the pleural invasive area: haematoxylin and eosin staining of the submerged fixed specimen shows invasive adenocarcinoma with pleural retraction (yellow oval) and a fibroelastotic scar (*yellow star). C, Corresponding elastin staining of A, showing elastin (black) in the lung as well as fibrosis (red) in the pleural retraction invaded by small acinar adenocarcinoma beyond the outer elastic layer (yellow arrowheads). D, Corresponding cytokeratin 7 staining to A, highlights cytokeratin 7-positive cells (brown). C-N, collapsed nonmalignant area; C-T, collapsed tumour area. Vascular invasion If a pathologist is in doubt about whether a histological structure is an artery or a vein, elastin staining may help in the recognition of vascular structure and thereby invasion by tumour cells: the elastic fibers in the tunica media of the pulmonary arteries will designate the vascular lumen.
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