Pulmonary intestinal-type adenocarcinoma does not show enteric differentiation by immunohistochemical study.

Six cases of an unusual variant of primary pulmonary adenocarcinoma resembling colorectal and sinonasal adenocarcinoma are presented. Pulmonary intestinal-type adenocarcinoma occurs in elderly Caucasians and is associated with a histology characteristic of colorectal/enteric adenocarcinoma: a garland-like architecture with a 'gland in gland' periphery, central 'dirty' necrosis, and elongated stratified columnar cells, lacking significant goblet or signet ring differentiation. While a resemblance to intestinal adenocarcinoma by light microscopy is present, immunohistochemical studies comparing these carcinomas with metastatic colorectal adenocarcinoma clearly show a respiratory phenotype with the neoplastic cells expressing thyroid transcription factor-1 and cytokeratin 7 to the exclusion of cytokeratin 20, and failing to express CDX-2. Stains for a variety of epithelial mucins (MUC1, MUC2, MUC5AC) also support this observation. The differential diagnosis with other pulmonary adenocarcinomas, especially those with mucinous differentiation, is discussed.