Carcinoma in situ is not benign, as long as it carries the word cancer, it is definitely a malignant tumor. However, carcinoma in situ is the earliest malignant tumor in terms of clinical stage, which is usually stage 0. At this time, cancer cells have just started to form and have not broken through the mucosa layer, so they cannot touch the lymphatic vessels and blood vessels, so the chance of lymphatic metastasis and distant metastasis is equal to 0. At this time, it can be cured by surgical resection, and other treatments such as radiotherapy and chemotherapy are usually not needed after surgery, as long as regular observation is done. In situ cancer of esophagus or intestine does not even require conventional surgical resection, but only endoscopic resection.