Atypical hyperplasia occurs most often in squamous epithelium, but can also occur in glandular epithelium. If the entire epithelium is involved, it is called severe atypical hyperplasia. Severe atypical hyperplasia is a precancerous lesion that is surgically removed and usually does not spread. Severe atypical hyperplasia is a condition in which the cells, in the process of proliferation, develop a proliferative differentiation that is not necessarily the same as that of normal tissue cells, i.e., heteroplasia, and is generally used primarily to describe lesions of the epithelium. Heteroproliferative epithelium has cellular and structural heterogeneity, but does not always progress to cancer; some heteroproliferative growths can be reversed and disappear when the causative factors are removed. It is the cancer or sarcoma that has the characteristics of metastasis and dissemination, which precancerous lesions generally do not have. On the other hand, the process of surgical removal of diseased tissue will generally expand the surgical scope appropriately and will ensure that the envelope of the diseased area is intact, and the surgery will take out the whole diseased tissue, so that the spreading and spillage of the cells will not generally occur. Although severe atypical hyperplasia is not cancer, when there is a higher chance of developing into cancer, it is recommended to seek timely medical treatment and standardize the treatment.