TTF1 and lung cancer: The pulmonary tumoral immunophenotype (positive for TTF-1, Napsin A, CK7; negative for CK20, p40, synaptophysin, and chromogranin A) confirms the diagnosis of primary lung ADC and invalidates the hypothesis of a metastasis arisen from a gastric adenocarcinoma or other forms of lung cancer.<h4>Conclusion</h4>The importance of the ancillary test is to distinguish a primary tumor from a metastatic one.