Common types of colorectal neuroendocrine tumors

Colorectal cancer is a common intestinal tumor. Colorectal neuroendocrine tumors are a group of tumors originating from neuroendocrine cells at the base of the intestinal crypts. They have different morphologies and degrees of malignancy due to different degrees of differentiation. They can be divided into the following five types based on morphology and biology.

1. Carcinoid: It is more common in the large intestine and rectum, followed by the cecum, sigmoid colon and descending colon. It is a group of well-differentiated neuroendocrine tumors, which appear as solitary submucosal nodules or polyps, with a diameter of less than 1 cm. The tumor cells are relatively small and uniform in size, columnar or cubic, with slightly eosinophilic cytoplasm and small particles. The nuclei are round or oval and relatively uniform in size. The carcinoid located in the colon is larger, with an average diameter of about 5 cm, and its histological structure is basically the same as that of carcinoids in other parts of the body.

2. Adenocarcinoid: Also known as goblet cell carcinoid, it is common in the appendix but may also occur in other parts of the body. Under the microscope, goblet cells or signet ring cells similar to those seen in signet ring cell carcinoma can be seen, arranged in tiny glandular tubules and small nests. Its biological manifestations are between those of ordinary carcinoid and adenocarcinoma.

3. Adenocarcinoma: Adenocarcinoma is a mixed carcinoid. The cancer tissue has a mixed structure of both carcinoid and adenocarcinoma components, and its biological behavior is the same as that of adenocarcinoma.

4. Small cell carcinoma: Similar in biology to small cell carcinoma of the lung, it is a highly malignant neuroendocrine tumor. The tumor cells are small and uniform, with dense and evenly distributed chromatin, inconspicuous nucleoli, and frequent nuclear division phases. Necrosis of tumor tissue is common, and it is more common in the right colon. It is a highly malignant tumor.

5. Large cell neuroendocrine carcinoma: A malignant neuroendocrine tumor of the large intestine composed mainly of large cells in organoid nests, beams, rosettes and palisade structures. The tumor cells have abundant cytoplasm, vacuolated nuclei and prominent nucleoli.