Adenocarcinoma is a type of malignant epithelial tissue tumour that originates from the glandular epithelium. Microscopically, adenocarcinoma cells form adenoid structures of varying size, shape and arrangement, often irregularly arranged in multiple layers, with nuclei of varying sizes and nuclear schizophrenia. When the adenocarcinoma is accompanied by a large number of papillary structures, it is called papillary adenocarcinoma; when the cavity is highly dilated and cystic, it is called cystic adenocarcinoma; when it is accompanied by papillary growth, it is called papillary cystic adenocarcinoma. Mucous is found in the lumen of the gland and around the gland, which is called mucinous adenocarcinoma.