Previous studies comparing the outcomes of segmental resection and extensive resection strategies for SCRC patients have exhibited comparable rates of grades II and III postoperative morbidities [14]. In addition, patients subjected to EXT may experience more severely compromised bowel function and life quality, even after long-term adaptation [1, 14]. However, for patients who are diagnosed with SCRC at a young age, those with a strong familial inheritance of the disease, those with multiple/metachronous lesions, or those who are more genetically susceptible to cancers, EXT may represent a better option than segmental resection [4, 6]. Therefore, it is crucial to compare the outcomes of EXT and segmental resection in various SCRC cohorts to enrich our knowledge on the two surgical strategies, thereby guiding the clinical treatment of the disease.

Unlike previous reports [15,16,17,18,19,20,21,22,23,24], we recruited a cohort of SCRC patients whose lesions were located in separate segments and compared the differences between LHS and EXT. Our study showed that LHS did not increase the incidences of surgical complications and AL compared with EXT. In addition, OS, DFS, and the incidence of metachronous colorectal cancers were all similar between the two groups. However, the LHS group tended to have a decreased number of daily bowel movements and a lower percentage of major LARS cases compared with the EXT group. Multivariate analysis further confirmed the N stage as the only factor that could independently predict OS and DFS in SCRC cases involving separate segments, whereas surgical strategy had no significant impact on the patients’ survival. Ours is the research comprehensive comparing the surgical results, incidence of metachronous colorectal cancer, and long-term oncological outcomes between LHS and EXT for non-HNPCC patients with SCRC involving separate segments based on a relatively large SCRC cohort. More importantly, we analyzed the impact of a surgical method on functional sequelae (in terms of defecation function and LARS) in this cohort.

LHS involves two anastomoses, namely an ileocolonic anastomosis and a colorectal anastomosis. The preserved left branch of the middle colon artery, left colonic artery, and inferior mesenteric artery can ensure blood supply in the residual left hemicolon. However, the risk of ischemia in the left hemicolon will be increased if the operator is inexperienced with the ligation of key blood vessels. At present, there are few studies on whether the ileocolonic anastomosis will affect the safety of colorectal anastomosis. Holubar et al. stood the point that synchronous double colon anastomoses may not increase the risk of developing complications and are a safe regimen for certain patients, and there were no anastomotic leaks or fistulas in 69 patients subjected to double colonic anastomoses [7]. In a previous study, Takatsu et al. retrospectively analyzed 42 patients who underwent laparoscopic (n = 27) and open (n = 15) double colon resections and anastomoses, the AL rate was 9.5% (3.7% and 20.0% in the laparoscopic and open surgery groups, respectively), and these data indicate that laparoscopic surgeries for SCRC are safe and have more short-term benefits than open surgeries [25]. The overall AL rate in our cohort was 5.1%, and the AL rate was 4.9% for the LHS group, similar to the rate of ileorectal/ileosigmoid AL (5.7%) for the EXT subgroup. As for operative time, it should be noted that although an additional anastomosis was performed for the LHS group, the mean operative time for this group was 48 min shorter than that for the EXT group, which may be ascribed to the dissociation of left hemicolon and the use of ileal pouch during the EXT procedure.

We also investigated whether LHS will increase the incidence of metachronous colorectal cancer in the left hemicolon or affect the radicality. Our results showed that the 103 patients in the LHS group did not develop metachronous cancer during the long-term follow-up. At the same time, OS and DFS exhibited no significant differences between the LHS and EXT groups. Our study excluded cases with FAP and regularly performed colonoscopy examinations for patients. Our standard postoperative surveillance was to perform the 1st colonoscopy examination at 1 year after surgery; for patients with polyps before surgery, the 1st colonoscopy was performed to remove the polyps at 3 months after surgery. Thereafter, a colonoscopy was performed once a year. In this way, precancerous lesions were removed to prevent them from developing into cancer lesions. Therefore, for our cohort, there was no re-operation due to metachronous cancers during the follow-up. We further analyzed the prognostic factors for SCRC involving separate segments within a median follow-up duration of 51 months. The results confirmed that lymph node metastasis status could independently affect both OS and DFS for SCRC involving separate segments, while the surgical strategy (LHS or EXT) did not significantly affect the patients’ OS and DFS.

The colon plays key physiological roles in defecation and maintaining fluid balance. Patients who are about to undergo colorectal operations often expect an altered bowel function and thus seek counseling preoperatively. A previous study [14], which was designed to predict postoperative functional outcomes and quality of life after colonic resections of different lengths, demonstrated that the patients had to contend with frequent stools after the surgeries. In addition, the concurrent analyses of the study also indicated restricted preoperative social activity, housework, recreation, and travel due to the altered bowel function after EXT. In our study, the mean numbers of daily bowel movements were 3.8 in the EXT group (similar to that reported in the study mentioned above) and 1.3 in the LHS group. In this study, we also utilized the LARS score to compare surgical outcomes of LHS and EXT. Our findings indicated that patients with major LARS scores in the LHS group were less than those in the EXT group. These findings further confirmed the benefits of preserving the left hemicolon on bowel function in SCRC cases involving separate segments.

Our study has several limitations that ought to be mentioned. First, our study has inherent limitations due to the retrospective nature and the relatively small number of participants. Second, the bowel function scale was partially lost, and the quality of life was not scored. In addition, some of the patients may not have achieved stable functional outcomes at the time of the survey. Third, the follow-up data were incomplete, and some variables such as the occurrence of benign polyps in the left hemicolon were not described in detail. In view of these limitations, our conclusions warrant further validation by prospective studies that include more participants, adopt more detailed and longer follow-up, and perform more objective bowel functional assays. Nevertheless, so far as we know, we recruited the largest cohort of SCRC patients reported so far to confirm that LHS has acceptable surgical safety and AL rate, better preserves bowel function, and possesses similar long-term oncological outcomes as compared with EXT.