CEACAM5 and adenocarcinoma in situ: Although lung tumors containing ciliated cells are usually benign, CMPT still shows some low-grade malignant tumor features such as destroyed alveolar structures and central fibrosis, proliferation along the alveolar walls and skip lesions similar to adenocarcinoma in situ, no encapsulation, and positive carcinoembryonic antigen staining [1].