Adenomas are tumor-like lesions formed by the proliferation of glandular epithelial cells or mucosa, which are not cancerous, but have a tendency to become cancerous. Adenoma cells are generally highly differentiated, similar to normal cells, and are benign lesions. Cancer cells are poorly differentiated and are malignant, which can affect the patient’s life expectancy to some extent. When adenomas increase in size, they may become malignant, especially choroidal adenomas of the colorectum, gallbladder adenomas, thymic adenomas, and gastric adenomas. Imaging examinations that describe adenomas that are significantly larger than before and show signs of liquefaction and necrosis indicate that adenomas are more likely to be malignant. When adenomas are found, it is important to go to oncology or related departments, such as thoracic surgery for thymoma and head and neck surgery for thyroid adenoma, to choose the right treatment plan as soon as possible under the guidance of doctors to avoid cancerous changes.