179 Pattern recognition in pulmonary AdC; a modified classification In the OLVG Amsterdam, 218 patient cases were retrieved from the pathology archives, whereas from San Raffaele archive in Milan 365 patient cases were retrieved. The flow diagram of selection of suitable cases is shown in figure 2. A total of 135 fulfilled the study criteria. After random selection in total 80 cases were included. Freshly cut sections of the selected paraffin blocks from both institutes were stained for H&E, elastin (Elastica von Gieson, EvG) staining206 (see for Standard Operation Procedure (Dutch) Supplementary files), and CK7 immunohistochemistry (IHC) at the department of Pathology of the VUmc. Both institutes used neutral buffered formaldehyde for the fixation of their resection specimens. Histological review of these cases was performed by three pathologists (HB, FF, ET). For each case, one representative tumour block was selected and digitized. The digital images were uploaded on the collaborative platform for on-line teaching, training and quality assurance in pathology, Pathogate (https://pathogate.net). After technical review of the cases, 10 were excluded, mainly because of insufficient quality of the slide, including out-of-focus areas after scanning. Therefore, 70 cases, 35 from each institute, were further analyzed. Subtyping of the adenocarcinomas according to the WHO was performed by 2 pathologists (HB, FF) in the categories AIS, lepidic predominant adenocarcinoma (LPA), low grade adenocarcinoma (acinar, papillary) with or without > 10% high grade component and high-grade adenocarcinoma (micropapillary, solid). Cases with discrepancies (dominant pattern, presence of high-grade component) were reviewed, reaching consensus. Mathematical model In order to understand and demonstrate the effect of collapse, we tried to construct a mathematical model, starting from a cube with equal ribs as an approximation of an alveolar space. In this model, an approach was used with reduction in size to a progressively flatter box, where the total circumference of the ribs remains the same. The effect of progressive flattening on surface area and volume was calculated. As the alveolar architecture is sometimes compared to a bunch of regular and dried grapes, 318 the analogous example of grapes and raisins is shown in Figure 3. Pictures were taken from grapes, both fresh and after 3 weeks of dehydration. Slices were embedded in paraffin blocks and section were stained with H&E. We formulated the following hypothesis: i) alveolar walls will be folded in iatrogenic collapse and ii) due to increased pressure by decrease of alveolar surface, the tumour cells may increase in length in prominent collapse. 14
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