Intra-Alveolar Intestinal Epithelium: A Reappraisal of the So-Called Mucinous Goblet-Cell Rich Carcinoma Apropos of Two Cases With Prolonged Follow-up and Literature Review.

Primary pulmonary mucin-rich lesions with abundant goblet cells growing within alveolar spaces are either classified as mucinous adenocarcinoma (previously called mucinous bronchioloalveolar carcinoma) or colloid carcinoma. Some of these lesions display a morphologic pattern characterized by paucicellular discontinuous patches of nonatypical colonic type epithelium attached to alveolar walls without evidence of invasion. Immunohistochemically, these epithelial patches express an intestinal immunophenotype (CD20+, CDX-2+, CK7-, TTF-1-). None of the lesions so far reported with these histological and immunohistochemical characteristics have recurred or metastasized. Herein we describe 2 patients with this type of intra-alveolar mucinous lesions who have been meticulously followed-up for 9 and 14 years, respectively, without evidence of disease progression. Based on their histologic appearance, immunoreactivity, and on the presence of occasional CDX-2 expressing cells in terminal airways adjacent to the lesions, we propose alternative interpretations of the mucin-producing epithelium. More important, a separate provisional category for these lesions is suggested that eliminates their force inclusion as adenocarcinomas.