Tumor Sidedness Could be a Prognostic Factor in Patients with Stage II Colon Cancer

Background : The search for high-risk factors in stage II colon cancer (CC) is ongoing and several high-risk factors for stage II CC have been identified; however, the effects of tumor sidedness on prognosis is not clear. This study aims to determine whether tumor sidedness could be identified as another high-risk factor for stage II CC. Methods : We retrospectively analyzed 189 patients with stage II CC, following consecutive curative resection surgery performed between 2008 and 2014. We compared clinicopathological findings and long-term outcomes between the patients with right colonic cancer (RCC) and patients with left colonic cancer (LCC). Prognostic factors for survival were determined using univariate and Cox proportional regression analyses. Results : A total of 72 patients were diagnosed with RCC and 117 patients were diagnosed with LCC. Patients with RCC were significantly older (p < 0.001) than those with LCC, and the number of harvested lymph nodes (HLNs) was greater in the RCC group (RCC: 25 vs. LCC: 19; p = 0.003). The overall survival (OS) was notably worse in the RCC group than the OS in the LCC group (5 year survival rate—RCC: 81.3% vs. LCC: 90.4%; p = 0.025), whereas no significant difference was observed in disease-free survival (5 year survival rate—RCC: 74.8% vs. LCC: 83.4%; p = 0.065). Cox proportional regression analysis showed that tumor sidedness (hazard ratio (HR): 3.78, 95% confidence interval (CI): 1.61–8.85, p = 0.022), gender (HR: 3.27, 95% CI: 1.27–8.47, p = 0.014), and the number of HLNs (HR: 4.58, 95% CI: 1.95–10.74, p < 0.001) were independent prognostic factors for OS. Conclusion : Patients with a right-sided primary tumor location have more negative prognostic factors and worse long-term outcomes than those with a left-sided primary tumor location in stage II CC.

there are several high-risk factors, according to the guidelines of the National Comprehensive Cancer Network, the European Society for Medical Oncology, and the Japanese Society for Cancer of the Colon and Rectum (JSCCR) [6][7][8]. These include bowl obstruction, perforation, poorly differentiated histology, lymphovascular invasion, perineural invasion, pT4, low number of harvested lymph nodes (HLNs; <12), and unclear resection margins. However, these risk factors vary by region, and there is still no rigorous evidence. The search for other prognostic factors in stage II CC is ongoing. For decades, carcinogenetic differences between right colonic cancer (RCC) and left colonic cancer (LCC) have been suggested [9,10]. Also, there have been reports of differences in clinical, pathological, molecular, and biological features, according to the tumor sidedness, and there has been much debate about the impact of tumor location on prognosis [9,11,12]. Nevertheless, few reports have evaluated tumor sidedness as a risk factor of stage II CC, because many of these reports target advanced stage cancers, including metastatic CRC, to analyze the differences in chemotherapy effects. In these advanced stage and metastatic CRCs, molecular and biological differences are considered when selecting a chemotherapy regimen [13,14]. Meanwhile, investigations into the effects of adjuvant chemotherapy on stage II CRC have not yet been concluded; the main problem being that the high-risk factors have not been identified. Therefore, the current challenges are to identify the high-risk factors and evaluate the benefits of adjuvant chemotherapy. Previous studies of adjuvant chemotherapy for stage II CRC were designed to identify survival benefits, with the focus mainly on high-risk patients [15,16]. The problem, however, is that most of the previous studies of stage II CRC have not evaluated tumor sidedness. In this study, we hypothesize that differences in tumor sidedness define the prognosis of stage II CC. This study aims to determine the influence of tumor sidedness on the long-term outcomes and prognosis for stage II CC.

Method Patients
Subjects for the study were selected from patients with CRC at the Department of Surgery, Saiseikai Yokohamashi Nanbu Hospital, between January 2008 and December 2014. The inclusion criteria were as follows: (1) patients with stage II colonic adenocarcinoma without rectal cancer, based on the Union for International Cancer Control's (UICC) TNM classification (seventh edition); (2) patients had undergone surgery with R0 resection; and (3) patients without synchronous or metachronous malignancy. The selected patients were divided into two groups, based on tumor location (the RCC and LCC groups). RCC was defined as a tumor arising from the cecum, ascending colon, or transverse colon. LCC was defined as a tumor arising from the descending colon, sigmoid colon, or recto-sigmoid colon.
Surgical procedure and follow-up The procedures were performed by colorectal surgeons (with the patients under general anesthesia) and involved a complete mesocolic excision. The method of surgical approach (open surgery or laparoscopic surgery) was determined in each case, depending on the patient's medical history and tumor progression. Laparoscopic surgery was performed using five trocars. Adequate resection margins were determined according to JSCCR guidelines, and D2 or D3 lymphadenectomies were performed in all cases [8]. All patients were followed up regularly at our institution, including carcinoembryonic acid (CEA) and cancer antigen 19 − 9 assays every 3 to 6 months, and computed tomography every 6 to 12 months. A colonoscopy was performed annually, for at least 5 years.
Adjuvant chemotherapy was offered to all high-risk stage II patients having at least one high-risk factor, according to the JSCCR Guidelines for the Treatment of Colorectal Cancer. Treatment was started after pathological evaluation of the tumor specimen, which was performed within 8 weeks of surgery, under informed consent. In adjuvant chemotherapy, oral 5-fluorouracil prodrug (capecitabine) was taken by the patient for 6 months following the operation.

Evaluation of surgical outcomes and prognostic factors for survival
We retrospectively compared patient characteristics, including age, gender, and pathological findings, between the RCC group and the LCC group. Tumor histology was described using the World Health Organization classification [17]. Pathological staging was performed according to the UICC's TNM classification. The surgeries were organized by procedure type, and the data included the extent of lymph node dissection, the number of HLNs, duration of surgery, volume of blood loss, postoperative stay, and complications. Postoperative complications were described using the Clavien-Dindo classification; grade II or higher was considered a major complication in this study [18]. Postoperative results included pathological findings, recurrence rate, overall survival (OS), and disease-free survival (DFS).

Statistical analysis
Statistical analysis included the Student's t-test, which compares the mean of a continuous variable with a parametric distribution, and the Mann-Whitney U test, for variables with nonparametric distributions. The chi-square test or Fisher's exact test were used to compare proportions. Survival was estimated by the Kaplan-Meier method, and the group data were compared using the log-rank test. Prognostic factors for survival were determined using univariate and Cox proportional regression analyses. All tests were two-tailed and P-values < 0.05 were considered to be significant.

Results
Demographic and clinicopathological characteristics, and surgical outcomes A total of 1,398 CRC patients underwent resective surgery at our hospital between January 2008 and December 2014. Of those, 189 patients with stage II CC were extracted, based on the inclusion criteria; 72 were diagnosed with RCC and 117 were diagnosed with LCC. Demographic and clinicopathological characteristics are summarized in Table 1. Patients with RCC were significantly older (p < 0.001) than the LCC patients, and the number of HLNs was significantly higher in the RCC group (RCC: 25 vs. LCC: 19; p = 0.003). Gender, serum CEA level, tumor diameter, histological type, the incidence of preoperative obstruction and tumor perforation, and the other pathological data did not differ between the two groups. There was no significant difference in the incidence of postoperative complications (Clavien-Dindo classification ≥ II) between the two groups (p = 0.08). A total of 27 patients (14.3%) received adjuvant chemotherapy, and there was no difference in the rate of adjuvant chemotherapy between the two groups (RCC: 12.5% vs. LCC: 19.4%; p = 0.40).     [3,13,19].
In related studies, it was reported that defective mismatch repair genes, high microsatellite instability (MSI-H), BRAF/KRAS mutations, and CpG island methylator phenotype positive were the notable characteristics of RCC, whereas LCC was characterized by frequent NRAS and p53 mutations [4,13,[20][21][22]. These molecular and genetic features of CC that were due to the tumor location have been associated with prognosis, and the treatment, such as 5-fluorouracil-based chemotherapy or anti-EGFR therapy [19,23,24]. Meanwhile, in stage II CC, the efficacy and role of adjuvant chemotherapy is still uncertain [16,25]. In addition, there is an ongoing debate over which factors are high risk in the prognosis for stage II CC. Although tumor sidedness is not included as a stage II high-risk factor in the current guidelines, attention must be paid to tumor location in view of these molecular biological differences. year of study [28]. These findings are compatible with our results.
One notable evaluation factor based on tumor sidedness is the number of HLNs. In stage II CRC, current guidelines suggest that fewer than 12 lymph nodes harvested is considered a high-risk factor [6,7]. Low lymph node yields may result in positive lymph nodes being missed and increase the risk of under staging [29,30] reported that the total number of HLNs was higher in the RCC group (11.7 vs, 8.3 ; p = 0.0001), and these results are similar to our own findings [32]. The reason for this was due to the differences in the resected area, depending on the tumor location. The right-sided colon mesentery may anatomically contain a more complex lymphatic system and a larger area of resection, when compared with the left-sided colon [33,34]. Therefore, the reference value for the number of lymph node dissections may be better considered separately for each tumor location.
In this study, tumor sidedness was not an independent prognostic factor for DFS, although a certain trend was observed (p = 0.065). However, tumor sidedness is an independent factor for OS in stage II CC. We speculate that RCC could have a greater potential for malignancy with poor biological behavior, once it has recurred, when compared with LCC. Therefore, our results strongly indicate that RCC should be considered as a risk factor for stage II CC. In addition, it is necessary to develop multidisciplinary treatment strategies that include tumor sidedness, as well as pathological and genomic factors.
This study has some limitations. First, the small sample size, retrospective design, and single-center setting may limit the generalization of results. Second, this study did not include the status of BRAF/KRAS/NRAS mutations, MSI, sporadic mismatch repair deficiency, germline mutation-prompted Lynch syndrome, or any family history. These genomic and epigenomic characteristics should be considered, in addition to the tumor location. Therefore, it is necessary to conduct randomized controlled trials with a large sample size, including genomic information, at multiple institutions across different countries, to confirm the prognostic factors in stage II CC.

Conclusions
In conclusion, this study revealed that tumor sidedness was an independent prognostic factor for OS in stage II CC. We strongly suggest that tumor sidedness should be considered as a high-risk factor in stage II CC patients, in addition to the traditional factors.