Although significant advances have been made in colorectal cancer management, major changes have been suggested for rectal cancer. The principals of colon cancer surgical resection have remained fairly constant. The key to achieving oncologically safe resection is to obtain clear resection margins and removal of the locoregional lymph node bearing mesentery.

Apart from a few challenging cases, colon cancer is relatively easy to handle and it has a wide operative field compared to rectal cancer. Therefore, concerns regarding bowel margins are limited to only a few unusual cases. The adequacy of proximal and distal resection margins for colon cancer is primarily defined by vascular ligation and hence the adequacy of the vascular supply to the intended anastomotic segment. Although not clearly defined, it is generally agreed that 5 cm bowel margins are sufficient to allow resection of mural tumor spread [1]. Some data suggests that mural tumor migration is rarely greater than 2 cm, either proximally or distally, to the palpable tumor edge [2]. In addition, there was a report postulating that adequate clearance of the mesocolon containing the vascular and lymphatic system is more important for colon cancer surgery [3].

The proximal bowel resection margin is one of the surrogates of surgical quality: however, in some cases, it is difficult to obtain ≥5 cm proximal resection margins (PRM). For example, in patients with proximal sigmoid colon cancer, ≥5 cm PRMs cannot be obtained by anterior resection without splenic flexure mobilization. Therefore, we need to assess the influence of PRMs on oncologic outcomes to establish a surgical standard for colon cancer.

The aim of this study was to assess the association of the length of the PRM with other surrogates of surgical qualities such as the number of retrieved lymph nodes, stage, distal resection margin and to analyze the influence of PRM on oncologic outcome.

In the present study, we determined that PRM length is not associated with oncologic outcome among patients with sigmoid colon cancer. For sigmoid colon cancer patients, the PRM is determined according to the level of ligation of the inferior mesenteric artery because this affects the adequacy of the vascular supply to the intended anastomotic segment. The relation between PRM length and oncologic outcome has not been taken into consideration in these patients. The intramural spread of colorectal cancer up to 4 cm is well described in previous pathological studies and forms the basis of the “5 cm rule” in determining resection margins for rectosigmoid and rectal cancer [1,4]. However, the length of the distal resection margin has been challenged. A previous study showed that 94% of patients with rectal cancer had distal intramural spread less than 2.5 cm, suggesting that patients with intramural spread greater than 2.5 cm were those with poorly differentiated tumors [5].

It is now accepted that extending the resection margins further to include intramural spread may not affect survival rates, since most of these patients are more likely to die from the presence of distant metastases than from local recurrences. Hence the presence of distant intramural spread may be an indicator of poor prognosis. Since then, many studies have been performed to prove that shorter distal resection margins are acceptable in terms of oncologic outcomes [6-8] in an effort to preserve the sphincter, especially in patients with rectal cancer.

PRM, however, has not been in the consideration because enough PRM could be easily got for patients with colon cancer. In some case, unnecessarily immoderate PRM might be obtained for patients with sigmoid or rectal cancer without evidence of benefit of excessive PRM.

Studies have been performed to determine the most adequate surgery for patients with colon cancer. Resection of the intact mesocolon has been suggested based on the concept that the colonic mesentery or mesocolon contain the vascular and lymphatic drainage systems of the colon and therefore adequate clearance is likely to have the same oncologic benefit as total mesorectal excision [3]. The authors reported that meticulous mesocolic plane surgery is associated with improved overall survival [9]. They did not indicate bowel resection margins as one of the determinants of oncologic outcome. A second analysis of the COST trial [10] insisted that in the setting of technical credentialing and monitoring, surgical quality surrogates, including proximal and distal resection margins, mesenteric length, and number of retrieved lymph node, did not correlate with cancer outcomes. The “rule” of PRM length needs to be reconsidered, based on these results.

Resection of enough long proximal resection margin is not difficult for patients with colon cancer most of the cases. However, we would encounter situation whether to resect excessive bowel or get less enough proximal resection margin in some cases such as patients with proximal sigmoid colon or sigmoid-descending junction colon cancer. Proximal resection margin was determined by the adequate vascular supply to anastomosis. Anastomotic leakage occurred in one patient with ≥5 cm PRM in the present study. Short PRM did not associate with anastomotic complication.

Luminal recurrence was one of the concerns for short PRMs as the length of the PRM was guided by the extent of the intramural spread of the tumor [1]. In the present study, most recurrences (96.4%) occurred among patients with distant metastases. Anastomotic recurrence developed only in one patient who had ≥5 cm PRM. Therefore, a shorter PRM does not appear to increase the risk of local recurrence. PRM length was not associated with local recurrence or anastomotic complications. Rather it would be better to be evaluated in terms of association with systemic metastasis. PRM length was associated with the extent of mesocolic excision, including lymphatic and vascular drainage. We analyzed the association between PRM length and the number of retrieved lymph nodes and determined that these two factors were independent. Tumor size, lymphovascular invasion, perineural invasion, distal resection margin length, and pathologic stage were also independent of PRM length, meaning that a shorter PRM was not associated with less extensive resection in terms of the pathologic surrogate of surgical extent.

We analyzed the influence of PRM length on surgical and oncologic outcomes according to tumor sub-location because short PRMs could be more common among patients with proximal sigmoid or sigmoid-descending junction cancer. As expected, patients with a PRM length <5 cm were more frequently identified in the SDPS group, although surgical and oncologic outcomes did not vary according to PRM length in relation to tumor sub-location.

This study has a few limitations that should be considered when interpreting the results. There remains a potential for both referral and selection bias, as the study was a retrospective and observational cohort study performed at a single-institution. Despite the large sample size, the relatively small number of patients in the PRM <5 cm sub-group did not make a significant impact on the RFS comparisons. In addition, we examined PRM length as a categorical variable with a cut-off of 5 cm, as this was the recommended guideline, but there is a possibility that this does not reflect the continuous impact of PRM on oncologic outcomes. In addition, we could not suggest the adequate proximal margin which did not compromise oncologic outcome because of small number of subgroup with shorter than cm PRM. However, we did evaluate the relationship between PRMs and other pathologic variables in order to compare surgical extents according to PRM length. From these observations we can conclude that a shorter PRM was not associated with anastomotic complications, increased local recurrence, or poor oncologic outcomes.

In conclusion, this large single-institution study on sigmoid colon cancer patients demonstrated that a PRM length <5 cm is not considered a less extensive resection. PRM length did not affect the oncologic outcomes. This relationship was also observed among patients with proximal sigmoid/sigmoid-descending junction cancer. In addition, regardless of PRM length, most recurrences were systemic metastasis and were most tightly associated with the pathologic stage. In conclusion, excessive bowel resection in order to obtain longer PRMs should be done in moderation on these patients.