Ductal adenocarcinoma accounts for 80%-90% of pancreatic adenocarcinoma. Ductal adenocarcinoma is mainly composed of glands with different degrees of differentiation of duct-like structures, accompanied by abundant interstitial fibers. Highly differentiated ductal adenocarcinoma is mainly composed of well differentiated duct-like structures lined with highly columnar epithelial cells, some of which are mucinous-like epithelium and some of which have abundant eosinophilic cytoplasm. This carcinomatous duct is sometimes difficult to distinguish from residual and hyperplastic ducts in the setting of chronic pancreatitis. The moderately differentiated ones consist of duct-like structures with different degrees of differentiation, some of which are similar to highly differentiated adenocarcinomas, and some of which may have realistic cancer nests. The low-differentiated ones only have a few irregular glandular lumen-like structures, and most of them are solid cancer nests with great cellular anisotropy, ranging from undifferentiated small cells to tumor giant cells or even multinucleated tumor giant cells, and sometimes spindle cells can be seen; in the few areas with glandular lumen-like differentiation, there can be a small amount of mucus, and the interstitium of the tumor is rich in type I and IV collagen. 2.Special types of carcinoma of ductal origin ① Polymorphic carcinoma: also called giant cell carcinoma, which may be a subtype of ductal carcinoma. It is composed of oddly shaped mononuclear or multinucleated tumor giant cells, or even spindle-shaped cells, which may sometimes resemble osteoblastic giant cells or choriocarcinoma-like cells. The tumor cells are arranged in solid nests or in a sarcoma-like arrangement. Adenosquamous carcinoma: Occasionally seen in the pancreas, it may be the result of squamous malignant transformation of pancreatic duct epithelium. The tumor consists of adenocarcinoma and squamous carcinoma components. Pure squamous carcinoma is quite rare in the pancreas. (3) Mucinous carcinoma: The cut surface can be jelly-like, very similar to the colonic colloid carcinoma. Under light microscopy, the tumor contains a large amount of mucus, forming a mucus pool. Cells may be suspended in it or scattered at the edge of the mucus pool. Mucinous epidermoid-like carcinoma and indolent cell carcinoma: Occasionally seen in the pancreas. Ciliated cell carcinoma: The morphology is the same as that of general ductal carcinoma, characterized by some cells with cilia. The tumor cells are polygonal, round or short columnar in shape. The nucleus is round and often located at the base. The tumor cells are arranged in vesicular or lacunar shape, and the cytoplasm is strongly eosinophilic and granular. Both electron microscopy and immunohistochemistry show the characteristic features of adenosarcoma cells, such as abundant rough endoplasmic reticulum and zymogen granules. Adenoid cell carcinoma mainly metastasizes to local lymph nodes, liver, lung or spleen. Small glandular carcinoma is a rare type of pancreatic cancer. It is more common in the head of pancreas. Microscopically, the tumor consists of many small glandular structures and solid nests with slender fibrous septa between them. The cells may be cuboidal or columnar in shape, with relatively uniform nuclei. Recent studies suggest that this type of pancreatic cancer may be a compound tumor of alveolar cells and endocrine cells. 5.Large eosinophilic granular cell carcinoma This type of tumor is rare, its tumor cells have abundant eosinophilic granular cytoplasm, round or ovoid nuclei, and arranged in small nests. There are fibrous septa separating them. The cytoplasm of electron microscopic tumor cells is filled with hypertrophic mitochondria. Small cell carcinoma of the pancreas is morphologically similar to small cell carcinoma of the lung and accounts for about 1% to 3% of pancreatic adenocarcinoma. It is composed of consistent small round cells or oat-like cells with little cytoplasm and many nuclear divisions, often with hemorrhagic necrosis and positive NSE immunohistochemical staining. Most die within 2 months. Its origin is unclear.