The incidence of multiple primary cancers of the colon is 2-5%. It is the second most common site of multiple primary cancers after skin or breast. Including simultaneous multiple primary cancers and heterochronous multiple primary cancers, more than two cancers occurring in different parts of the colon or diagnosed less than 6 months apart are called simultaneous multiple primary cancers. Cancers occurring in different parts of the colon at different times more than 6 months apart are called heterochronous multiple primary cancers. It is easy to be missed or misdiagnosed clinically. In our gastroenterology department, 19 cases of multiple primary cancers of colon and 11 cases of heterochronous multiple primary cancers were found in the past 5 years. They are analyzed as follows: Yu Yisheng, Department of Surgery, Baotou Poverty Alleviation Hospital, Baotou City, China 1 Clinical data: 8 cases of simultaneous multiple primary cancers of the large intestine in this group. All of them were male, aged 40-69 years old, with an average age of 55 years old. There were 11 cases of heterogeneous multiple primary carcinoma of the large intestine, including 6 males and 5 females. They were aged 30-72 years, with a mean age of 51 years.Among the 8 cases of synchronous multiple primary cancers, 6 cases were diagnosed by preoperative colonoscopy and 2 cases were found by intraoperative exploration. Simultaneous multiple primary cancers were all found by colonoscopy, and the time of discovery was from 6 months to 2 years after the first radical operation.2 Discussion2.1 Simultaneous multiple primary cancers are rare in clinic, which may easily lead to underdiagnosis or misdiagnosis. Clinically, some progressive colorectal cancers cannot be examined by colonoscopy due to the blockage of intestinal lumen by tumor, and it is easy to miss the cancer foci in other parts of the colon. In this group, there is one case in which a lesion in descending colon was found by preoperative colonoscopy, but there was a lesion in the liver area during intraoperative probing. Therefore, clinicians should be fully aware of the simultaneous multiple primary cancers of the large intestine, and intraoperative exploration of the whole colon should be a routine. However, for small lesions of the colon, especially those located in the hepatic flexure, splenic flexure, and rectum, intraoperative examination is easy to miss the diagnosis only by the sense of touch, so it is advocated that intraoperative colonoscopy should be carried out, with the help of the operator into the mirror, in order to find new lesions and avoid the missed diagnosis. In addition, intraoperative specimen dissection should be emphasized as a routine. If multiple cancer foci or accompanying polyps are found after specimen dissection, the scope of surgery should be re-decided according to the lesions. Among the preoperative examinations, fiberoptic colonoscopy and biopsy are preferred, which has a significantly higher diagnostic rate for colorectal cancer than lower gastrointestinal angiography, especially for the early lesions that are easier to find. If colon cancer is found by barium enema before operation, rectal fingerprinting and sigmoidoscopy should be performed to avoid missing low-grade cancer; on the contrary, after rectal cancer is diagnosed, barium enema or fiberoptic colonoscopy must be performed to exclude primary cancer of the 2nd and 3rd above the rectum. It can also be combined with other examination means such as ultrasound and CT examination to improve the preoperative diagnosis rate. 2.2 Heterochronous colorectal cancers are missed and misdiagnosed because of the failure of postoperative review of the first primary cancer, which leads to the missed diagnosis of the second primary cancer. Incomplete understanding of the pathologic diagnosis of heterochronous multiple primary cancers. It is difficult to recognize whether it is primary cancer or recurrence, metastasis, which leads to misdiagnosis. We should cooperate with pathologists to obtain a clear pathologic diagnosis before surgery, and adopt a positive attitude towards surgery for patients without clear signs of metastasis. Regular postoperative colonoscopy is very important, the first time is 3 to 6 months after surgery, and then once a year for 3 years. 3 years later, not once every 2 to 3 years. Colonoscopy helps to detect adenomas and treat them endoscopically, effectively preventing them from evolving into multiple primary cancers in the future. The diagnosis of recurrent metastasis should not be made easily for colorectal cancer foci detected by postoperative colonoscopy, so as not to delay the treatment of second primary cancer. Author：Yu Yisheng Gastrointestinal Surgery Department, Gastroenteroscopy, Baotou Poverty Alleviation Hospital, Baotou City, China Title：Attending Physician Tel：13171459677 E-mail:[email protected]