GGO is actually a clinical imaging description, and the term translates to mean ground glass lesions. Glassy lesions are seen in a variety of diseases, most commonly in lung infections, which are inflammatory diseases of the lung; in interstitial lung diseases, such as interstitial pneumonia and pulmonary fibrosis; in pulmonary edema, which in most cases is associated with cardiac insufficiency; and in allergic diseases, such as allergic pneumonia and eosinophilic pneumonia, all of which can be seen as GGO. GGO can also be seen in early stages of the entire tumor, and early lung cancer lesions can also have GGO as the main manifestation, but of course the decision needs to be made on a patient-by-patient basis.