Intestinal type of lung adenocarcinoma (ILADC) was initially described by Tsao and Fraser in 1991. Morphology and immunophenotype of ILADC are the same as in colorectal adenocarcinoma. Rectocolonoscopy must be performed to exclude colorectal origin of adenocarcinoma. Colorectal adenocarcinoma claimed to be genetically similar to an ILADC. Patients. We describe 24- and 26-year-old patients of both genders who went under surgery because of a lung tumor mass detected on CT scan. ILADC was diagnosed on resected lung specimens. According to positivity of Cytokeratin20, CDX-2, and Villin, respectively, and negativity of Cytokeratin7, TTF-1, Napsin-A, SurfactantB, MUC-1, and MUC-2, respectively, ILADC was diagnosed. KRAS mutation was detected in tumor tissue of the male patient. Conclusion. Rectocolonoscopy is the only relevant method for distinguishing the intestinal type of lung adenocarcinoma from metastatic colorectal carcinoma because immunohistochemistry and detection of mutation status are frequently the same in both types of adenocarcinoma. More investigations are needed for further understanding of ILADC in purpose of personalized lung carcinoma therapy particularly introducing detection of mutation status, especially in younger patients. 1. Introduction In the last few decades, adenocarcinoma is the worldwide most common histologic subtype of lung carcinoma. It develops more frequently than any other histologic types of lung carcinoma in no smokers, particular in women. Intestinal type of lung adenocarcinoma ILADC [1, 2] was not mentioned in WHO lung carcinoma classification from 1999 to 2004. In recent years, International Study Group of Lung Carcinoma introduced ILADC in adenocarcinoma classification [3–5], but this variant of lung adenocarcinoma was initially described by Tsao and Fraser in 1991, and it was characterized by a predominant component of malignant tall, stratified columnar, and goblet cells [6]. Immunophenotype of ILADC is the same as in colorectal adenocarcinoma. Malignant cells are positive for Cytokeratin20 and CDX-2 and negative for Cytokeratin7 and TTF-1 [7–9]. Rectocolonoscopy must be performed in order to exclude colorectal origin of adenocarcinoma. Patients reported in the respected literature were older than patients in our study [9]. It is well known that EGFR and KRAS gene mutations act as positive and negative predictors, respectively, of therapeutic response to EGFR targeted therapies in colorectal adenocarcinoma. This tumor claimed to be genetically similar to ILADC [10]. Here we describe 24-year-old and 26-year-old
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