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National Cancer Institute U.S. National Institutes of Health
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Epithelial hyperplasia
Increase in number of cuboidal, columnar, ciliated or mucous cells without atypia. Cells maintain normal architecture of bronchioles and alveoli. The main distinctive features of regenerative hyperplasia are absence of direct link to tumor progression, and presence of inflammation and necrosis due to the inflicting toxic agent.
Neuroendocrine hyperplasia
Groups of uniform small cells with scant cytoplasm and round to oval nuclei with dense speckled chromatin form clusters thickening bronchiolar wall and/or protruding into the lumen. Immunohistochemical staining for markers of neuroendocrine differentiation, such as synaptophysin, CGRP and chromogranin, is required for accurate identification. Not reported to occur spontaneously. Neuroendocrine hyperplasia must be differentiated from normal groups of neuroendocrine cells found more prominently in some mouse strains.