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. 2019 Oct 1;32(5):266–277. doi: 10.1089/jamp.2018.1517

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© James Verco et al., 2019. Published by Mary Ann Liebert, Inc.

This Open Access article is distributed under the terms of the Creative Commons License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

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FIG. 2. — H&E photomicrographs. (A) Group 1: General distribution of undifferentiated, pleomorphic, large, anaplastic tumor cells within alveolar spaces or lining the alveolar septae. The majority of cells do not have features of adenocarcinoma and appear in sheets of contiguous tumor. Many cells have basophilic staining cytoplasm, while others are large, anaplastic and contain pale amphophilic staining. Note the presence of a preexisting resident population of alveolar macrophages. (B) Group 2: General distribution of large expansive tumor mass filling most alveolar spaces as well as neoplastic cells in the periphery. Most tumor cells are predominantly undifferentiated, pleomorphic, large, anaplastic with pale amphophilic staining. Immune cell infiltration are predominantly neutrophils and macrophages. (C) Group 2: Peripheral tumor masses with multiple smaller masses filling alveolar spaces. Tumor cells are pleomorphic, large, anaplastic with pale amphophilic staining. Tumor regression is present at the nodule peripheries with infiltration of macrophages. (D) Group 4: Previously populated tumor masses assessed by areas of residual fibrous connective tissue, central collagenous stroma and fibrocytes. Alveolar spaces are commonly filled with lymphocytic infiltrate. (E) Group 5: General distribution of regressing tumor masses. Regressing masses are variably small and randomly distributed. Fibrous connective tissue is seen filling/replacing alveolar spaces and suggests foci of regressing adenocarcinoma. Acute necrosis, fibrous connective scaffolding, mixed cell infiltration of macrophages, giant cells and lymphocytes in the epithelium, and stroma signifying tumor regression. (F) Group 6: Tumor regression is evidenced by previously populated tumor masses in multiple small areas of fibrous connective tissue replacing the alveolar spaces with a central collagenous stromal core, with thickening of the septae and fibrocytes infiltrating the alveolar spaces suggesting foci of previous adenocarcinoma cells. H&E, Hematoxylin and Eosin.