To the Editors:

We deeply appreciate Dr. Taflampas and colleagues’ interest in our manuscript entitled “Prognostic impact of inferior mesenteric artery lymph node metastasis in colorectal cancer.”1

They raised several important questions regarding our manuscript. The first issue was the high local recurrence rate in the IMA-negative group in our study. In the results, the isolated local recurrence rate (0 vs. 4.4%) and overall local recurrence rate (3 vs. 8.6%; p = 0.51) were higher in the IMA-negative group, but there was no statistical significance. However, the question remains why the local recurrence rate in the IMA-negative group is high. It is hard to say whether it is a real difference or a result of bias from the small number of patients in the IMA-positive group. The local recurrence after the curative resection of colorectal cancer could be affected by various factors, such as the T stage of the primary tumor, the N stage, lymphovascular invasion, level of anastomosis from anal verge, circumferential resection margin, and the surgeon’s technique.2,3 As Dr. Taflampas mentioned, more meticulous dissection for the enlarged IMA lymph node group might have played a therapeutic role in reducing the local recurrence rate in the IMA-positive group. Because of the limitations of a retrospective study design, it is very difficult to control for an individual surgeon’s bias to the extent of the surgery, but we believe that the dissection technique had been consistent during the study period in our center.

Another possibility is that “time to recurrence” may influence the recurrence patterns. In our study, the median time to systemic recurrence in the IMA-positive group was shorter than IMA-negative group (12.5 vs. 18.7 months; p = 0.238), although not significant. This phenomenon might have originated from the aggressive behavior of the tumor biology or microscopic systemic dissemination features in the IMA-positive group. For these reasons, the number of local recurrences could have seemed to be lower than it really was in the IMA-positive group.

In this study, patients who had metastases to the IMA lymph nodes showed a high incidence of systemic recurrence and poor prognosis. When we looked into the details of the recurrence pattern, the recurrence on para-aortic lymph nodes was a variable, which caused a statistically significant difference. There was no difference between two groups’ recurrence rates for the liver, lung, or peritoneum, even though the percentage of recurrence in the liver and peritoneum was higher in the IMA-positive group. Further study is needed to clarify the impact of IMA lymph node metastasis on other types of distant metastases.

With this study, we wanted to point out the importance of the anatomical distribution of metastatic lymph nodes. The clinical impact of the metastases to the IMA lymph nodes is not only a prognostic factor but also a predictive factor of potential metastases to para-aortic lymph nodes. Therefore, the patient who had metastases to the IMA lymph nodes might be a candidate for para-aortic lymph node dissection because the patient’s prognosis could be improved by the complete removal of micrometastases. This is another hypothesis to be validated.

Again, we want to express our sincere thanks to Dr. Taflampas and colleagues for their precise comments and valuable discussion.