Background: Several factors such as submucosal invasion more than 1000µm, lymphovascular invasion, positive resected margin, poorly differentiated histological grade are reported as risk factors of lymph node (LN) metastases of invasive submucosal CRC in the Japanese Society for Cancer of Colon and Rectum (JSCCR) guidelines. According to the guidelines, we re-evaluated the risk factors of lymph node metastases and examined patients’ long-term outcomes.
Patients and methods: We retrospectively analyzed 400 patients with submucosal CRC treated by endoscopically and/or surgically at Osaka Medical Center for Cancer and Cardiovascular Disease, Japan from 1984 to 2008. We classified patients to two groups, high-risk group that had any of these risk factors, and low-risk group that did not have any of them. We could follow 327 patients more than 3 years. We assessed lymph node metastases, distant metastases and 5-year survival.
Results: The rates of 5-year disease-free and overall survival were 98% and 100% in low-risk group, and 94% and 96% in high-risk group. The risk factors of LN metastases were histologic grade (muc/sig/por, P<0.001) and lymphatic invasion (P=0.001). The risk factors of distant metastases were histologic grade (muc/sig/por, P=0.001), lymphatic invasion (P=0.003), venous invasion (P<0.001), the tumour location (rectum/proctos, P=0.037) and LN metastases examined after surgical resection (P=0.003). There were no significant differences in submucosal invasion and positive margin.
Conclusion: According to the treatment guideline for invasive submucosal CRC disease-free and overall survival did not differ between two groups. However, histologic grade and lymphatic invasion are only significant factors of LN metastases in our retrospective study. From the results of long-term outcomes, the tumor location (rectum/proctos) is a new risk factor of distant metastases in addition to other factors relating LN metastases. It suggests re-evaluation of risk factors regarding LN metastases and prognosis is necessary, confirmed by prospective study.