Early stage carcinoma refers to carcinoma in situ with early infiltration; the so-called early stage refers to only microfocal infiltration. Early infiltration of gastrointestinal cancer means that the infiltrating cancer cells are still within the mucosal layer; early infiltration of squamous cell carcinoma of the official neck means that the scope of the infiltrating foci is limited to the interstitium from the basement membrane to a depth of 3 mm. This infiltration can only be seen under the microscope. It is generally believed that those with infiltrating foci less than 1mm in depth will not be accompanied by lymph node metastasis and can still be treated as carcinoma in situ; for those with infiltrating foci greater than 1mm and less than 5mm in depth, a few of them can have metastasis. Microscopic cancer refers to cancer of very small size, and the criteria of microscopic cancer in various organs are different. Microscopic carcinoma of liver or small liver cancer refers to a single cancer nodule or two adjacent cancer nodules with the sum of diameters less than 3 cm. clinically, it is mostly asymptomatic, so it is also called subclinical liver cancer. Microscopic carcinoma of the stomach refers to carcinoma with a diameter of less than 1cm. Occult carcinoma refers to the primary carcinoma is very small, which is not detected clinically, but metastatic carcinoma is detected first. For example, the diameter of occult papillary thyroid cancer is less than 1cm, and the center of the lesion is fibrous scar tissue with scattered papillary cancer tissue and infiltration to the surrounding thyroid tissue. Although the tumor is small, it metastasizes early, and 2/5 cases have metastasis in the cervical lymph nodes before surgery.