163 Elastin in pulmonary pathology neofibrogenesis) is characteristic of stromal invasion. Usually, these tumour cells have high-grade atypia. Tumour areas with desmoplastic stroma and/or other classic characteristics of invasion do not form part of the above discussion regarding a collapsed AIS/lepidic pattern and papillary adenocarcinoma. Artefact A seemingly focal increase in elastin content occurs in cases of pulmonary collapse after surgery as an ex-vivo artefact: the bronchiolar epithelial layer folds because of the smooth muscle contraction. Underneath this folded epithelial layer is an accumulation of recoiled elastin120. Remarkably, the simple epithelium lining in vivo is flexible enough to pile up as small folds in in the bronchiolar lumens of lungs with iatrogenic collapse. It is not excluded that, in collapsed AIS, some piling of the tumour cells on alveolar walls may occur. If this does not consistently exceed a thickness of two cell layers, early data support an excellent prognosis305. Conclusions Overall, iatrogenic collapse may have a profound effect on the microscopic appearance in pulmonary adenocarcinomas. Perfusion fixation, as routinely used in some centres, may mitigate this effect. Elastin staining is useful for the distinction between AIS with iatrogenic collapse and papillary carcinoma. Use of elastin staining should be considered, in order to make the most accurate diagnosis. 12
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