Carcinoid tumors are tumors of neuroectodermal origin, originating from the amine precursor uptake and decarboxylation system, and are the most common neuroendocrine tumors of the rectum. They are well-differentiated, slow-growing neuroendocrine tumors that border between benign and malignant tumors and are less likely to metastasize, but have potential for metastatic recurrence. The liver is the most common metastatic organ. Clinical manifestations Rectal carcinoid tumor occurs at a low site and has no specific symptoms in the early stage, the most common ones are anorectal discomfort and blood in stool. The most common symptoms are anorectal discomfort and blood in stool. As the disease progresses, lower abdominal pain, shortness of breath, blood in stool and change in bowel habit may appear. Rectal carcinoid tumor cells are mostly non-silverophilic and are usually not accompanied by carcinoid syndrome. Histopathology Rectal carcinoid tumor shows small cell carcinoma with small tumor cells. CgA (chromogranin) is a sensitive and specific marker for neuroendocrine cells; high Ki-67 positivity rate indicates proliferation of tumor cells, aggressiveness and poor prognosis. Ancillary examinations Colonoscopy is the most helpful examination for rectal carcinoid tumor, and pathology can also be taken for clear diagnosis, endoluminal ultrasound of rectum, CT and MRI of abdomen and pelvis are performed for clear analysis, and CT examination of liver and lung is also recommended. Main treatment modality Surgery The treatment of carcinoid tumor is determined according to the tumor size, infiltration depth and lymph node degree, and surgery is still the main treatment. Most of the tumors <1cm are benign and 1.7% are malignant, which can be locally resected by colonoscopy, which is safe and reliable and can preserve intestinal function; 10% of 1cm-2cm are malignant, and if infiltration of superficial muscular layer may have higher malignancy rate, intestinal segment resection should be performed; 82% of >2cm are malignant, or after local resection, infiltration of muscular layer and obvious ulcer on the surface are found, which should be operated according to the scope of radical rectal cancer. Biosuppressive therapy The most commonly used are α-interferon and growth inhibitor therapy. Interferon can activate natural killer cell function and control hormone secretion and tumor proliferation. Growth inhibitors (commonly used octreotide) can prevent tumor cells from releasing neuroendocrine hormones, which can inhibit tumor proliferation and prolong survival. Chemotherapy For advanced carcinoid tumors, cytotoxic drugs can be used for chemotherapy. Capecitabine, oxaliplatin and dacarbazine have certain therapeutic effects. Prognosis The prognosis of rectal carcinoid tumor is related to the size of tumor, infiltration scope, and the presence of metastasis, and rectal carcinoid tumor has the best prognosis among all carcinoid tumors.