Colorectal tumors have special characteristics histologically compared to other gastrointestinal tumors. Tumors confined to the colorectal mucosa are not at risk of regional lymph node metastasis and do not exhibit malignant biological behavior. Therefore, western pathologists attach great importance to the significance of histological depth of infiltration in the diagnosis of colorectal cancer and precancerous lesions. 2000, WHO proposed the classification criteria for gastrointestinal tumors, which pointed out that only microscopically detected colorectal tumor tissue penetrating the mucosal muscle layer and having the basis of submucosal infiltration can be diagnosed as “cancer”, and the following criteria were applied The original mild and moderate heterogeneous hyperplasia are classified as low-grade intraepithelial neoplasia (LGIN), while lesions with histological features of cancer but lacking ISM evidence, such as severe heterogeneous hyperplasia, carcinoma in situ and intramucosal carcinoma, are classified as high-grade intraepithelial neoplasia (HGIN). Currently, this criterion is being promoted in China in the field of clinicopathological diagnosis of colorectal tumors. E-colonoscopy is an important tool for early diagnosis and early treatment of colorectal cancer, but the introduction of the concept of HGIN into the pathological diagnosis of colonoscopic biopsy has caused a series of problems and confusion to the diagnosis. I. Problems in the diagnosis of HGIN by colonoscopy 1. High rate of too low diagnosis: If the pathological diagnosis is made in full accordance with the new WHO criteria, preoperative colonoscopic biopsy often occurs to underestimate the lesion. The results of several prospective studies at home and abroad showed that a total of 310 cases were diagnosed as HGIN by colonoscopic biopsy, while 289 cases were confirmed as invasive carcinoma by postoperative pathology, and the incidence of underdiagnosis of lesions was as high as 93.2% in total. 2. Low rate of definite diagnosis of ISM: Several studies have retrospectively read the preoperative colonoscopy biopsy specimens of 1347 patients with postoperative pathological confirmation of invasive carcinoma, and found that 836 cases were diagnosed as HGIN in the colonoscopy biopsy specimens, and the proportion of cases in which ISM could not be determined reached 62.1%. Second, the reasons for the limitations of the diagnosis of HGIN by colonoscopy 1, the limitations of sampling: the tissue clamped by colonoscopic biopsy is too little or too shallow, and the clamped tissue often does not contain the submucosa, or although it contains the submucosa, it fails to contain the typical ISM tissue. Some studies suggest that the larger the diameter of the biopsy tissue, the higher the probability of definite ISM, and it is easier to judge when the maximum diameter reaches about 0.5 cm. Also, increasing the number of grains taken for biopsy (more than 6 grains) can help the pathological diagnosis of malignant lesions; however, some studies also show that the difference in the number of biopsy grains has no effect on the correct diagnosis. Therefore, the most reasonable explanation for not finding the submucosal layer in colorectal tumor biopsy tissue is that the tumor has destroyed the submucosal layer. 2. The heterogeneity of adenoma carcinoma tissue: the results of a large number of epidemiological, pathological and clinical studies suggest that adenoma is an important pre-cancerous lesion of colorectal cancer. The pathological diagnostic criteria of adenoma carcinoma are: on the basis of adenoma heterogeneous hyperplasia, some areas show enlarged nuclei and become round or ovoid; at the same time, nuclear chromatin becomes coarse and obvious nucleoli appear, or pathological nuclear division images appear; the polarity of nuclei is disturbed, epithelial cells lack mucus secretion, and adenoid ducts are irregular and closely arranged, appearing coelomic or sieve-like structures, or adenoid epithelial cells are hyperplastic and connected into a network. Therefore, the tissues characteristic of HGIN and adenocarcinoma may appear in the mass at the same time in adenoma carcinoma, and the colonoscopic biopsy sampling fails to capture the typical cancerous tissues, but only the tissues of HGIN, thus leading to the occurrence of preoperative biopsy overdiagnosis. 3. Misunderstanding of the diagnostic significance of HGIN: WHO stipulates that the diagnostic term HGIN can be used for lesions that have histological features of cancer but lack evidence of ISM. However, there are specificities in the application of this concept to colonoscopic biopsy specimens. A colonoscopic biopsy specimen contains only a small portion of the mass and does not reflect whether the entire lesion has ISM; therefore, a diagnosis of HGIN based on a colonoscopic specimen alone is not meaningful. Only the diagnosis based on the most heterogeneous part of the whole resected specimen is of value. Therefore, the diagnosis of HGIN is not recommended for colonoscopic biopsy specimens, and the term HGIN should be correctly understood and applied clinically to avoid mechanical diagnosis according to WHO’s criteria in colonoscopic biopsy specimens. For suspected cancer cases in which ISM cannot be determined by biopsy specimens, pathologists can combine other histological features of the tumor and clinicopathological characteristics to make a comprehensive diagnosis. First of all, the following histological manifestations found in the microscopic examination should be considered for the diagnosis of cancer: the presence of obvious heterogeneous glands in the normal mucosal background without excessive migration between the heterogeneous glands and the surrounding normal glands; the size and morphology of the heterogeneous glands are very different and the distribution is uneven; the interstitium between the heterogeneous glands is not a loose tissue of the intrinsic membrane but a denser fibrous tissue; the histological manifestation of tumor necrosis. Secondly, pathologists should pay attention to the combination of gross colonoscopic findings, ulcerative lesions, bulging ulcerative lesions or tumors without a tip, fixed at the base, involving more than 1/3 of the circumference of the intestinal canal, and the characteristics described in the previous section should be clearly diagnosed as cancer when seen histologically. In the study by Yingqiang Shi et al, it was found that for tumors diagnosed as HGIN by colonoscopic biopsy, the mean maximum diameter of tumors confirmed as invasive carcinoma after surgery was 3.65 cm, while the mean maximum diameter of tumors confirmed as HGIN after surgery was only 1.50 cm in four cases. therefore, the size of volume is an important indicator to differentiate carcinoma from HGIN. Multiple adenomas with more than three, adenomas larger than 1 cm in diameter, adenomas with highly heterogeneous hyperplasia, villous adenomas, broad-based adenomas that have been comminuted and removed, and those with a family history of hereditary non-adenomatous bowel cancer are all high-risk adenomas with a higher likelihood of recurrence and carcinoma. Serrated adenoma is considered a new precancerous lesion, and studies have found that serrated adenoma can develop into invasive colorectal cancer within 2 years. Lesions with the above-mentioned features that have histological characteristics of HGIN should also be focused on the diagnosis of cancer. To address the limitations of colonoscopic biopsy, multi-point sampling with large grains can be adopted during colonoscopic biopsy to increase the detection rate of ISM. It is also reported abroad that endorectal ultrasound can be effectively used to determine the depth of rectal cancer infiltration, and its effect is significantly better than CT and MRI. Meanwhile, the detection level of colorectal precancerous lesions can be significantly improved by using pigmented endoscopy and magnified endoscopy techniques, especially the combined application of both – magnified pigmented endoscopy. In cases where the diagnosis is still not clear, the pathologist should recommend resubmission or describe the microscopic picture to suggest that invasive carcinoma cannot be excluded, with the word “at least” in front of the diagnostic name given, such as HGIN. It should not be overlooked that empirical diagnosis in the absence of ISM evidence has certain limitations, especially for small tumors, and there is a risk of overdiagnosis and overtreatment. Therefore, for the diagnosis of colorectal cancer, the diagnostic value of microscopic findings of ISM is irreplaceable. When it comes to low rectal cancer concerning the issue of preserving the anus, the requirement for finding definite evidence of ISM in the colonoscopic biopsy specimen is even higher if the diagnosis is to be made as a malignant lesion. Avoid overdiagnosis and overtreatment. This was also the original intention of WHO to introduce the new concept of HGIN. In 2002, the Vienna revised classification of gastrointestinal tract tumors proposed by several international congresses has clearly pointed out that the treatment plan for three types of lesions: preoperative diagnosis of low-grade mucosal neoplasia (including low-grade adenoma and low-grade heterogeneous hyperplasia), high-grade mucosal neoplasia [including high-grade adenoma or heterogeneous hyperplasia, non-invasive carcinoma (carcinoma in situ), suspicious invasive carcinoma, and intramucosal carcinoma], and submucosal invasive carcinoma need to be considered in combination with tumor size and the depth of tumor infiltration derived by ultrasonography and radiography. In summary, because colonoscopy biopsy specimens do not reflect the entire lesion, pathologists encountering cases with uncertain ISM should not only consider avoiding overdiagnosis, but should also be aware that the casual use of the diagnostic term HGIN to avoid diagnostic errors can result in a large proportion of malignant lesions being underdiagnosed. Therefore, it is important to avoid the mechanical diagnosis according to the WHO gastrointestinal tumor classification criteria for colonoscopy biopsy specimens, and to make a more definite diagnosis in combination with other pathological histological and clinical features of the tumor to provide a basis for clinical treatment.