185 Pattern recognition in pulmonary AdC; a modified classification Table 1. Revised adenocarcinoma classification based on evaluation of H&E, CK7 and elastin stainings. (continued) Surrogate markers of invasion “alveolar filling growth” All subtypes Growth within alveoli in ≧ 3 adjacent alveolar spaces The threshold of 3 adjacent alveolar spaces implies that the type alveolar filling growth should be consistently present and avoids the overlap with tangential cutting, especially in marked iatrogenic collapse. Solid Complete alveolar filling Complete alveolar filling is not seen in iatrogenic collapse. Cribriform Gland in gland formation The almost complete alveolar filling is not seen in iatrogenic collapse. Overlap with solid pattern may occur. Micropapillary Tufting, dissociation Beware of artifacts due to delayed fixation, which may not only be observed by detachment of tumour cells from the underlying stroma, but also by diffuse single cells. Papillary Fibrovascular cores without elastin Growth in alveolar space. Occasionally also in lumen bronchus/ bronchioles. Disturbed homeostasis of elastin is visible by variable amounts of elastin in pre-existing alveolar wall. In lumen of bronchus or bronchioles: lack of elastin. Alveolar macrophages usually absent. Grey zone Multilayering more than in tangential cut AIS, but not enough to fall in one of the other subtypes Recently, a slightly different approach was proposed and the “in between” zone was called “extensive epithelial proliferation”317. *) Minimal invasive adenocarcinoma and the so-called invasive pattern of STAS are not used in this classification. A flow chart of this morphologic approach is shown in Figure 7. 14
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