187 Pattern recognition in pulmonary AdC; a modified classification A graphical display and histologic examples of this morphologic approach are shown in the Figures 8 and 9. Figure 8. Schematic drawing of intra-alveolar growth 1) In collapsed AIS the pre-existing alveolar wall is recognizable by the elastin fibers (black). Above the schematic drawing is a CK7 staining with added elastin fibers. Seemingly papillary or acinar structures with thin walls containing elastin fibers are pre-existing alveolar walls (pseudo-papillary /pseudo acinar). In collapsed AIS the tumour growth is essentially a monolayer, where tangential cutting is a focal effect (part of an alveolus) that may lead to seemingly multilayering. 2) In the grey zone stratification is present in at least 3 adjacent alveolar spaces. This may also be seen close to the transition with non-malignant pneumocytes. 3) In micropapillary dissociation is frequently present. Tufting / micropapillae are minimally 3 cells tall and 2 cells wide. 4) “Gland-in-gland formation” also called “cribriform” is a form of acinar adenocarcinoma 5) Alveolar filling growth is a form of “solid” pattern. The cribriform and solid pattern prohibit alveolar collapse during resection. 6) Papillary carcinoma has fibrovascular cores, where the cores and the vessels therein do NOT contain elastin. 7) Note A): the amount of alveolar collapse in the tumour area is dependent of the number and structure of the tumour cells. If there are also alveolar macrophages present, this may reduce the possible collapse as well. Note B: all criteria associated with invasive growth should be present in at least 3 alveolar spaces. 14
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