Originates from serrated adenoma and/or has serrated morphological features

Similar to broad-based serrated lesions, the epithelium has a serrated structure, and secretion of mucus is common. It can be serrated, tubular, cribriform, lace-like, or beam-like. The cytoplasm is rich in mucus or eosinophilic, and the nuclei are vesicular.

More than 50% of tumor cells have significant intracytoplasmic mucus and no gland-like structures. If less than 50% of the tumor cells are signet ring cells, it is called adenocarcinoma with signet ring cells.

The tumor cells are diffusely distributed without the formation of glandular duct structures. The cytoplasm is rich in mucus components, pushing the cell nuclei to one side. They may also appear as round and centered nuclei without obvious mucus vacuoles.

Immunohistochemistry: CK20, CDX2, SATB2, MUC2, MUC5AC positive, CK7, ER negative.

Malignant epithelial tumors characterized by micropapillary architecture and unique biological behavior

The morphology is similar to micropapillary carcinoma in other locations. The tumor cells are in a clustered structure, surrounded by a lacunae-like structure similar to the vascular lumen, and a polar inversion phenomenon can be seen, that is, the top of the epithelium faces the periphery. The tumor cells have abundant, eosinophilic cytoplasm and pleomorphic nuclei. Vascular invasion is common. Elements of classic adenocarcinoma are often seen

(2) Immunohistochemistry: MUC1 epithelial tip staining (can indicate polar flipping phenomenon), SOX2, NOTCH3 positive

Poorly differentiated carcinoma characterized by solid growth pattern, pushing margins, and lymphoid-rich stroma

It is more common in the right colon and usually presents as a huge ulcer-shaped mass.

Immunohistochemistry: Caltetinin positive, CK20 positive (50%), CDX2 and CK7 mostly negative, MLH1 and MSH2 negative

Rare, low-grade adenocarcinoma with tubular and glandular features that occurs more commonly in patients with inflammatory bowel disease

Histological morphology, immunophenotype, and genetic characteristics are similar to those of hepatocellular carcinoma

Well-differentiated adenocarcinoma in which more than 50% of the tumor is composed of villous structures, also known as adenomatoid adenocarcinoma

The shape is similar to villous adenoma, showing infiltrative growth. The infiltration mode is pushing or invasive. It may contain rich mucus components, and epithelial island components can be seen in the fibrotrophic stroma.

Tumors with more than 50% composed of extracellular mucus are called mucinous carcinomas, and tumors with 10%-50% composed of extracellular mucus are called cancers with mucinous components. The mucus contains alveolar, clustered or single malignant epithelium, also known as colloid carcinoma.

The right colon is more common, and the cut surface is jelly-like

Under the microscope: nests, cords, clusters or single tumor cells can be seen floating in the mucus lake, signet ring cell components can be seen, and adenoma components can be seen next to the cancer in about 1/3 of the cases.

Immunohistochemistry: CDX2, MUC2, CK20, β-catenin (nuclear) positive, rectal cases CK7 positive, MUC6 negative, some cases MLH1 negative. Positive PAS and Alcian blue staining

Polyp type, mushroom type (exophytic type), ulcer type, annular constriction type or diffuse infiltration type, which can appear alone or mixed

Histological characteristics: 90%-95% of colorectal cancers are classic adenocarcinomas According to the ratio of glandular duct formation >95%, it is highly differentiated, <50% is poorly differentiated, and anything in between is moderately differentiated.

Microscopically: columnar epithelium with prominent atypia, frequent mitoses, fibrosis-promoting stromal reaction, necrosis, and inflammatory reaction.

Immunohistochemistry: More than 90% of colorectal cancers express CK20, CDX2, and SATB2 MSI-H tumors may show loss of expression of MLH1, PMS2, MSH2, and MSH6, and CK20 may be negative in these cases.