Fig. 2.

Variable immune cell infiltration within pulmonary AC in patients. a Lepidic growth pattern showing wide expansion (star) of alveolar interstitium by a diffuse population of mononuclear inflammatory cells, principally lymphocytes. Arrow indicates neoplastic cells. b A similar tumor showing minimal interstitial expansion (star) with few infiltrating inflammatory cells. Arrow indicates neoplastic cells. c Another lepidic growth region of AC showing focal expansion of the interstitium by lymphoid follicular hyperplasia (star). Arrow indicates neoplastic cells. d AC with infiltrating acinar pattern showing a desmoplastic (fibroblastic scarring) reaction (star) with very few infiltrating lymphocytes. Arrow indicates neoplastic cells. e AC with a papillary pattern demonstrating alveolar septae (arrow heads) with no fibrous expansion and no infiltration by lymphocytes. Arrow indicates neoplastic cells. Original magnification for images 100x