The difference between carcinoma in situ and benign tumor is that carcinoma in situ means that the tissue cells have already undergone malignant transformation, but the malignant cells are still confined to the mucosal layer and have not yet broken through the basement membrane, that is, they are at a very early stage. At this time, it must be treated, otherwise it will break through the basement membrane and spread and distant metastasis will occur. It is the most curable stage of malignant tumor. Benign tumors, as the name implies, are tumors that have not yet undergone malignant transformation and can be left untreated and only need to observe and wait. In conclusion, whether it is carcinoma in situ or benign tumor, pathological examination is needed to confirm. Benign tumors may turn into carcinoma in situ or even more advanced cancer with the passage of time. In contrast, carcinoma in situ will never turn into benign tumor. The differentiation and transformation from benign tumor to carcinoma in situ is an irreversible process.