Adenocarcinoma is a kind of malignant epithelial tumor with glandular structure or mucus secretion function, which mainly occurs in gastrointestinal tract, intrahepatic bile duct, bile duct (including gallbladder), lung, female reproductive tract and breast, and can also occur in tissues with glandular metaplasia, such as Barrett's esophagus and bladder with cystitis glandularis. Malignant tumor has the characteristics of differentiation to normal cells more or less. The closer the tumor cell differentiation is to normal cells, the more mature it is, which is usually called high differentiation. Some people call it Grade I.. If the tumor cells are poorly differentiated and extremely immature, but still retain traces of some tissues, it is called poorly differentiated, or called grade III. The boundary between the two is called middle differentiation, or class II. Generally speaking, well-differentiated tumors have low malignancy and good prognosis, poorly differentiated tumors have high malignancy and poor prognosis, undifferentiated tumors have extremely high malignancy and the worst prognosis.