Lymphatic dissemination of mid‐transverse colon cancer

Abstract

Park and colleagues address an infrequently studied issue in the field of colon cancer surgery, which is the optimal type of colectomy for treatment of tumours of the transverse colon [1]. They performed a retrospective comparative cohort study with all the inherent types of bias, but otherwise the study is of good methodological quality with detailed pathological assessment of the specimens and propensity score matching as a statistical strategy to decrease confounding. The primary aim was to explore the distribution of lymph node metastases between extended and transverse colectomies. After matching, 74 patients remained for definitive analysis and only 36 patients had nodepositive disease (18 patients per group). The authors adequately discuss the limitations of their study. How should we define midtransverse colon cancer? According to the authors, tumours located in the middle onethird of the transverse colon belong to this entity. But what is the scientific basis and how is this measured? When tumours are approaching the colonic flexures it becomes less clear. Should at least one of the edges of the tumour or the largest tumour bulk be located within the middleone third? There is also high interindividual variability in length of the transverse colon, which raises the question whether the onethird rule is applicable in every patient. Probably, variability in lymphatic drainage is gradually increasing with decreasing distance from each of the colonic flexures. Furthermore, tumour length might also influence the possibility of multiple routes of lymphatic dissemination. All these factors together complicate the interpretation of studies within this field. What should be the endpoint in such observational studies? If only looking at surgical specimens, one cannot evaluate what was left behind. On the other hand, regional nodal recurrences might be difficult to detect during followup. Parameters such as total lymph node count, lymph node count <12, or longitudinal resection margin are probably irrelevant for this specific research question. Removal of parts of the mesocolon that do not belong to the lymphatic drainage area of the tumour will improve such parameters, but without any impact on oncological outcome. Ultimately, only major postoperative complications, functional outcome and overall survival are relevant endpoints from a patient perspective, and these should ideally be evaluated in a randomised study with adequate sample size and clear definition of tumour location. Furthermore, there should be adequate quality control of surgical procedures with video analysis and postoperative imaging in such a trial. What we learn from small observational studies such as the study of Park and colleagues is that with high quality surgery for colon cancer by specialized surgeons who are part of a dedicated multidisciplinary team, the specific type of surgical procedures is probably less relevant. Very large trials with all their logistical challenges and high costs would be required to find the potential small differences in outcome for the different mesenteric lymph node dissections, if existing at all. In this study, there were no lymph node metastases found along the ileocolic pedicle. This implies that one might also think of resecting the transverse colon together with the hepatic flexure, with preservation of the ascending colon. This colon segment should be well vascularized and is also very mobile after full dissection from the retroperitoneum based on our experience with Deloyers procedure. Anastomosing the ascending colon to the splenic flexure should be possible from this perspective, and has likely better functional outcomes than extended right colectomy.