Today, a friend came to me in a great hurry, saying that the result of his wife’s operation was lung cancer, and they have been anxious these days, asking me what to do. When hearing lung cancer, most people would feel that the sky is about to fall, but there is a kind of lung cancer that we don’t need to worry about at all, which is my friend’s wife’s. Let’s take a look at the postoperative pathologic diagnosis. Let’s take a look at the postoperative pathological diagnosis: Pathology: partial lung of the left lower lobe, size 65*25*25mm, gray-red nodule on the cut surface, diameter 8mm, soft texture, poorly defined, 10mm away from the pleura, 20mm away from the cut edge of lung tissue. Examination result: adenocarcinoma in situ of the lung (partial lung of the right lower lobe). Cutting edge: no cancer involvement. The so-called adenocarcinoma in situ appears clinically to be the first stage of transformation of normal tissues into tumor cells after stimulation, often with atypical hyperplasia or carcinoma within the mucosal epithelium, but able to keep the basement membrane intact. From this point of view, adenocarcinoma in situ of the lung is actually not a cancer in the true sense. When the lesions produced by adenocarcinoma in situ of the lung within the epithelial cells continue to develop and the cells break through the basement membrane, it will evolve into microinvasive or invasive cancer. However, it may take about 10 years to complete such a process. Adenocarcinoma in situ of the lung grows more slowly and most of them are able to maintain stability for more than 10 years to avoid inducing cancer. As to whether adenocarcinoma in situ of the lung will definitely become invasive lung cancer, there is no definite conclusion yet. The new WHO Classification of Lung Tumor Tissues 2021 classifies atypical adenomatous hyperplasia and adenocarcinoma in situ together as precursor lesions of the gland (Precusorglandularlensions). This precursor to adenocarcinoma is included with the broader category of adenocarcinoma. In other words, the broad category of adenomatous hyperplasia and adenocarcinoma in situ is completely separated from the broad category of adenocarcinoma. Atypical adenomatous hyperplasia and adenocarcinoma in situ share almost the same benign biological behavior: they grow slowly and do not metastasize. What are the chest CT manifestations of adenocarcinoma in situ: (1) pure ground glass nodule (pGGN) of 5-30 mm, (2) uniform density, CT value below -600, (3) very few vacuoles, burrs, pleural pulling and lobulation, and (4) there can be blood vessels passing through but no vascular curvature. Of course, the diagnosis of adenocarcinoma in situ needs to be made with caution for pure ground glass nodules of more than 10 mm, and adenocarcinoma in situ of the lung is usually less than 10 mm. The publication of the new classification of lung tumor tissues by the WHO in 2021 has given us a great deal of guidance for the management of ground glass nodules in the lung. Adenocarcinoma in situ of the lung is defined as not a malignant tumor, adding to the strong evidence that adenocarcinoma in situ does not necessarily require surgery. Microinvasive adenocarcinoma, on the other hand, is an early malignant tumor with a very good prognosis and essentially no recurrence after resection. The need for resection and the timing of resection can be determined by a combination of the risk of the nodule itself, the patient’s wishes, and the risk of surgery.