Lung adenocarcinoma in situ refers to intraepithelial heterogeneous proliferation of cells involving the whole epithelial layer, but without breaking through the basement membrane below the epithelium. Invasive adenocarcinoma refers to tumor cells invading the basement membrane and breaking through the basement membrane to metastasize to distant sites. The details are as follows: Lung adenocarcinoma in situ: As the malignant tumor grows, its invasiveness increases. Cancer cells gradually grow and divide, spreading along the tissues and nerves. When the cell growth involves the whole epithelial layer downward but does not break through the basement membrane, it is called carcinoma in situ. When carcinoma in situ is detected, the condition is usually early, and timely drug and surgical treatments will give a better prognosis. Invasive adenocarcinoma: When the tumor cells continue to grow, invade and break through the basement membrane, it is called invasive carcinoma. As the basement membrane is locally damaged, cancer cells can migrate to distant places through the basement membrane, and blood and lymphatic channels can be the metastatic pathways. Therefore, if lung adenocarcinoma is detected, relevant examinations should be completed as much as possible to clarify the stage and grading of the cancer, and individualized treatment plan should be formulated according to the comprehensive evaluation of the condition, so as to improve the prognosis.