This video is a discussion of adenocarcinoma of the lung, especially with regard to pathologic diagnosis. Many things have changed in this area over the years; we discuss the state of the art in 2019. I am a medical doctor (a pathologist). My job involves diagnosing diseases such as lung cancer, mesothelioma, infections and interstitial lung disease by examining tissue samples under a microscope. I also teach medical students, pathology residents, and pulmonary and critical care fellows. I am the author of a textbook of non-neoplastic lung pathology published by Cambridge University Press. Check it out at: https://www.amazon.com/Non-Neoplastic. I also post freely accessible educational material related to pathology and lung diseases on Twitter (@smlungpathguy), Instagram (@smlungpathguy) and Facebook (my professional Facebook page is open to all). If you found this video to be useful, please like, comment, subscribe and share with your friends. It should be obvious but I’ll say it anyway: this video is for educational use only; this is NOT medical advice.