Primary enteric adenocarcinoma of lung (PEAC) (also referred to as pulmonary enteric adenocarcinoma) is an extremely rare tumor that has a striking resemblance to colorectal adenocarcinomas. It is composed of moderate to well-differentiated glands, often with cribriform pattern, lined by eosinophilic tall columnar cells with nuclear pseudostratification, dirty necrosis and nuclear debris. Lung is a common site of metastasis for colorectal adenocarcinomas. Given the vastly different treatment strategies and outcomes, PEAC of lung must be distinguished from metastatic colorectal adenocarcinomas. The diagnosis of PEAC of lung is rendered only after clinical exclusion of a primary tumor in the gastrointestinal tract. Immunohistochemical profile: Primary lung adenocarcinomas are generally positive for CK7, TTF1, Napsin A and negative for CK20, CDX2, and MUC2. However, PEAC of the lung frequently express some or all markers of enteric differentiation such as CDX2, MUC2 and CK20, in addition to the pulmonary markers. Villin may also be positive. It must be remembered that occasional cases of PEAC of lung may be CK7 negative and TTF1 negative and rare cases of metastatic colorectal adenocarcinomas in the lung may be TTF1 positive. Reference : C Wang et al. Pulmonary enteric adenocarcinoma : A study of the clinicopathologic and molecular status of nine cases. Int J Clin Pathol 2014;7(3):1266-1274.