"Early colorectal cancer" is defined by Japanese doctors as colorectal cancer limited to the mucosa or invading only the submucosa, regardless of the presence or absence of lymph node metastases.16
However, in this study, we evaluated the diagnostic accuracy of submucosal invasion for "early colorectal cancer-like lesions" instead of "pathologically confirmed early colorectal cancers." Only the gross features suggesting early colorectal cancer9
were used for the selection criteria.
The evaluation of early colorectal cancer-like lesions can be more practical than the evaluation of confirmed early colorectal cancers; this is because, first, it is not always easy to achieve endoscopic differentiate between a carcinoma and an adenoma or even between early cancer and advanced cancer. In other words, when an early colorectal cancer-like tumor is detected during a colonoscopy, we cannot confirm whether the lesion is an early colorectal cancer until the final pathology report of the resected specimen has been obtained. The role of forceps biopsy is also limited since the histopathology of endoscopic forceps biopsy disagrees with that of a resected specimen in 40% of cases.17
Second, when establishing therapeutic plans, it may be more important to determine whether the tumor is limited to the mucosal layer rather than whether the tumor is a carcinoma or an adenoma. Most mucosal neoplasms (revised Vienna classification categories 3 and 4:11
low grade adenoma/dysplasia, high grade adenoma/dysplasia, noninvasive carcinoma, and intramucosal carcinoma) can be treated by local excision (EMR or ESD) because lymph node metastasis is rarely reported without deep submucosal invasion.
The diagnostic accuracy for submucosal invasion was significantly improved by pit pattern analysis with MCE in this study. Moreover, the interobserver agreement of MCE was substantial, while the interobserver agreement of CWE was moderate. As such, MCE can estimate the depth of invasion for early colorectal cancer-like lesions more accurately and more objectively.
The diagnostic accuracy for submucosal invasion also significantly differed between CWE and MNE. However, the diagnostic accuracy did not differ between MCE and MNE. The estimation of submucosal invasion using MNE might be limited since the irregular microvascular pattern by the Showa classification could be interpreted in different ways. We considered an "irregular microvascular pattern" identified using MNE as a mucosal cancer without submucosal invasion. However, according to other studies,13
more than half of colorectal tumors with an irregular microvascular pattern showed deep submucosal invasion. In addition, microvascular classifications of colorectal tumors based on MNE had not been unified at the time of the study,14
and all of the expert endoscopists in this study were more familiar with pit pattern analysis using MCE than microvascular pattern analysis using MNE.
It is possible that the results would have been different if the endoscopists viewed the MNE images before the MCE images. In practice, MNE is performed before MCE because the applied dye used for chromoscopy interferes with MNE. However, in this study, estimation was performed earlier by MCE than by MNE because we set out to identify any additional effects of MNE on MCE for predicting submucosal invasion.
After the depth of invasion was estimated, we examined the cases in which the results of MCE and MNE did not agree among the endoscopists. The reasons for disagreement were mixed pit/microvascular patterns and bad images due to bleeding, exudation, or insufficient staining.
In conclusion, the estimation of submucosal invasion based on MCE or MNE is more accurate and more helpful for establishing a treatment strategy for colorectal tumors than the estimation based on CWE. MCE and MNE were demonstrated to have substantial agreement for estimating the depth of invasion.