266 Chapter 17 Figure 1. Photographs of a cucumber (papillary) structure taken at various angles. Note i) that if a papillary structure is randomly cut, the chance of observing an oval cross section is much higher than of a longitudinal cut. Note ii) that when in a histological slide a seemingly papillary structure is observed without corresponding oval cross sections, the correct interpretation with respect to the 3-dimensional structure is that the seemingly papillary structure represents a cross section through a structure with a surface (e.g., cross section through alveolar wall). Note iii) that the short axis is the same in all cross sections, while the long axis differs. The short axis is representative of the biology. Note iv) in serial sections the seemingly papillary structure can be continuously followed, as opposed to a true papilla, what disappears in serial sections120. Important is the recognition of desmoplastic stroma in pulmonary adenocarcinomas, what is almost invariably accompanied by isolated or small clusters of tumor cells. Look also at the CK7 staining to confirm the tumor cells in the corresponding area. Desmoplastic stroma may occur not in a pre-existing pulmonary architecture. The elastin staining may show several fragments or continuous lines of elastin, but this should not lead to a non-invasive interpretation as, the desmoplasia trumps the decision in favor of invasive adenocarcinoma. We established stricter histomorphological criteria for most of the surrogate markers of invasion in non-mucinous adenocarcinomas. These have a form of “alveolar filling growth” in the pre-existing alveolar space. If the lumen is almost completely filled such as in cribriform and solid growth, there will not be remaining air. Consequently, this part of the lung is not able to collapse during surgery. For the other alveolar filling growth patterns, the possible iatrogenic collapse will be related to the amount of remaining air.
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