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For clinically low-risk stage III colorectal cancer, the decision on cycles of adjuvant chemotherapy after surgery is disputed. The present study investigates the use of additional biomarkers of ploidy and stroma-ratio(PS) to stratify patients with low-risk stage III colorectal cancer, providing a basis for individualized treatment in the future.This study retrospectively enrolled 198 patients with clinical-low-risk stage III colorectal cancer (T1-3N1M0) and analyzed the DNA ploidy and stroma ratio of FFPE tumor tissues. The patients were divided into PS-low-risk group (Diploidy or Low-stroma) and PS-high-risk group (Non-diploid and High-stroma). For survival analyses, Kaplan-Meier and Cox regression models were used.The results showed that the 5-year DFS of the PS-high-risk group was significantly lower than that in the PS-low-risk group (78.6 vs. 91.2%, HR = 2.606 [95% CI: 1.011-6.717], P = 0.039). Besides, in the PS-low-risk group, the 5 year OS (98.2 vs. 86.7%, P = 0.022; HR = 5.762 [95% CI: 1.281-25.920]) and DFS (95.6, vs 79.9%, P = 0.019; HR = 3.7 [95% CI: 1.24-11.04]) of patients received adjuvant chemotherapy for 3 months were significantly higher than those received adjuvant chemotherapy for 3 months. We also found that the PS could stratify the prognosis of patients with dMMR tumors. The 5-year OS (96.3 vs 71.4%, P = 0.037) and DFS (92.6 vs 57.1%, P = 0.015) were higher in the PS-low-risk dMMR patients than those in the PS-high-risk dMMR patients.In this study, we found that PS can predict the prognosis of patients with stage III low-risk CRC. Besides, it may guide the decision on postoperative adjuvant chemotherapy.

Background: Our previous study has demonstrated an oncogenic role of PIWI-interacting RNA-54265 (piR-54265) in colorectal cancer (CRC). Here, we investigate whether it can be a blood biomarker for population screening and clinical applications. Methods: Serum piR-54265 levels were determined by a digital PCR method in 209 cancer-free healthy controls, 725 patients with CRC, 1303 patients with other types of digestive cancer and 192 patients with benign colorectal tumors. A prospective case-control analysis was conducted to assess the predictive value of serum piR-54265 for future CRC diagnosis. Receiver operating characteristic (ROC) curve was constructed to quantify the diagnostic performance of serum piR-54265 levels by assessing its sensitivity, specificity and respective areas under curve (AUC). The odds ratios (ORs) were computed using multivariate logistic regression models. Results: Serum piR-54265 levels were significantly elevated only in patients with CRC compared with controls and patients with other cancer types. The AUC for recognizing CRC was 0.896 (95% CI, 0.874-0.914), with a sensitivity and specificity being 85.7% and 65.1% at 1500 copies/µL as a cut-off value. The serum piR-54265 levels in patients declined substantially after surgery but increased significantly again when tumor relapses. The prediagnostic serum piR-54265 levels were significantly associated with future CRC diagnosis, with the ORs of 7.23, 2.80, 2.45, and 1.24 for those whose CRC was diagnosed within 1, 2, 3 and >3 years. Serum piR-54265 test is more sensitive than other blood CRC markers. Conclusion: Serum piR-54265 may serve as a valuable biomarker for CRC screening, early detection and clinical surveillance.

Background It was reported that tumor-expressed dickkopf-related (DKK) proteins affect micro-environment. However, the influence of DKK1 on colorectal cancer (CRC) liver oligometastases (CRCLOM) remains unclear. Methods CRC cases after resection of liver oligometastases were enrolled in Sun Yat-Sen University Cancer Center with intact clinical data. Serum DKK1 was detected by ELISA assay. Immunofluorescent staining examination for CD3 and CD8 in slices were also conducted. Results Among 65 patients included, the recurrence-free survival (RFS) and overall survival (OS) were significantly better in the low serum DKK1 group (RFS: P = 0.021; OS: P = 0.043). DKK1 was overexpressed in stage IV CRC patients in TCGA data. The number of CD8+ tumor-infiltrating lymphocytes (TILs) in invasive margin of CRC liver oligometastases was significantly higher in low serum DKK1 group (P = 0.042). Conclusion Elevated serum DKK1 level was associated with poorer RFS and OS, and less CD8+ TILs in invasive margin in CRC liver oligometastases. DKK1 might serve as a supplementalprognostic factor for clinical risk score and a potential target for immunotherapy.

Inflammatory conditions are common complications in colorectal cancer (CRC) and play significant roles in tumor progression and immunosuppression. However, the influence of inflammatory conditions on the tumor response to immune checkpoint inhibitors (ICIs) remains unclear. We included a high microsatellite instability (MSI-H) CRC patient whose primary tumor progressed and liver metastasis regressed after Pembrolizumab treatment. An organoid-T cell coculture model demonstrated an inhibited local immune response instead of systemic immunosuppression. Single-cell RNA sequencing suggested that neutrophils suppress the immune microenvironment, mostly through CTLA-4-associated pathways. A cohort of 73 patients with MSI-H CRC who received ICIs were enrolled, among whom inflammatory conditions were correlated with a poor tumor response. We demonstrated that inflammatory conditions in MSI-H CRCs correlate with resistance to ICIs through neutrophil-associated immunosuppression. Additional CTLA-4 blockade may improve the sensitivity to PD-1 blockade. Clinically, inflammatory conditions could predict a poor response to ICIs in MSI-H CRCs.

β2-microglobulin (B2M) and Janus kinases 1 and 2 (JAK1/2) mutations have been suggested as genetic mechanisms of immune evasion for anti-programmed cell death protein 1 (PD-1) therapy. Whether B2M and JAK1/2 lose-of-function mutation can cause primary resistance to anti-PD-1 therapy in colorectal carcinoma (CRC) patients remains controversial. Here, we sought to compare the efficacy of anti-PD-1 therapy in DNA mismatch repair deficient/microsatellite instability-high CRC patients with or without B2M or JAK1/2 mutations. Thirty-Five CRC patients who received anti-PD-1 therapy were enrolled in this study. All tumor samples underwent next-generation sequencing. The clinical and molecular data from 110 CRC patients sequenced with the Memorial Sloan Kettering-Integrated Mutation Profiling of Actionable Cancer Targets (MSK-IMPACT) assay and accessed through cBioportal were also analyzed in this study. Of the 35 CRC patients from our center, 10 (28.6%) had a B2M loss-of-function mutation, and 8 (22.9%) had a JAK1/2 loss-of-function mutation. Compared with B2M wild-type CRCs, B2M-mutated CRCs did not show a higher frequency of resistance to anti-PD-1 therapy (P=0.71). There was even better response to anti-PD-1 therapy in patients with JAK1/2 mutation than in those without (P=0.015). Of the 110 CRC patients in the MSK-IMPACT datasets, 13 (11.8%) had a B2M mutation, and 15 (13.6%) had a JAK1/2 mutation. After analyzing the response to anti-PD-1 therapy in these 110 patients, we found similar results (P=0.438 and 0.071, respectively). Moreover, patients with B2M or JAK1/2 mutation had a lower tumor mutational burden score compared with those without. B2M and JAK1/2 loss-of-function mutations occur frequently in microsatellite instability-high CRC. Our study demonstrated that patients with CRC harboring B2M or JAK1/2 mutations should not be excluded from anti-PD-1 therapy.

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BRAF and MLH1 promoter methylation testings have been proven effective prescreens for Lynch Syndrome. We aimed to compare different screening strategies for Lynch Syndrome in patients with MLH1(-) CRC. Patients with MLH1(-) CRC who had been tested for BRAF mutation and germline variants of DNA mismatch repair genes were included. We compared the sensitivities and specificities for identifying Lynch Syndrome and the cost-effectiveness of four screening approaches that used the following tests as prescreens: BRAF testing, MLH1 methylation testing, MLH1 methylation & BRAF testing, and MLH1 methylation testing & Revised Bethesda Criteria. Of 109 patients included, 23 (21.1%) were Lynch Syndrome patients. BRAF mutation and MLH1 methylation occurred in 6 (5.5%) and 40 (36.7%) patients, respectively. The sensitivity for identifying Lynch syndrome of BRAF testing was 100%, but the specificity was only 7%. MLH1 methylation testing had a lower sensitivity than BRAF testing (97.5% vs 100%), but had a markedly higher specificity (45.3% vs 7%). The combination of the two testings had a slightly higher specificity than MLH1 methylation testing alone (47.7% vs 45.3%). The MLH1 methylation testing approach had a 10% lower cost of identifying MLH1(-) Lynch syndrome carriers per case than universal genetic testing, but it missed 4.5% of patients. BRAF and MLH1 promoter methylation testings as prescreens for Lynch syndrome are less effective in Chinese patients with MLH1(-) CRC than in their Western counterparts. Universal genetic testing could be considered an up-front option for this population.

Background: A comprehensive investigation into immune cell infiltration provides more accurate and reliable prognostic information for patients with colorectal liver oligometastases (CLO) after liver metastasectomy. Methods: Simultaneous detection of the immune constituents CD3+, CD8+, Foxp3+ T, and &alpha, SMA+ cells in the liver oligometastasis of 133 patients was conducted using a four-colour immunohistochemical multiplex technique. Immune cells were quantified, and tumour-infiltrating lymphocyte (TIL) ratios were subsequently calculated. Correlation analysis was performed using Pearson&rsquo, s correlation. Recurrence-free survival (RFS) and overall survival (OS) for TIL ratios were analysed using the Kaplan&ndash, Meier method and Cox regression models. Results: Significantly fewer CD3+, CD8+, and Foxp3+ T cells were observed in the intratumoural region than in the peritumoural region of liver metastases. CD3+, CD8+, Foxp3+ T, and &alpha, SMA+ cells showed significantly positive correlations with each other both in the intratumoural and peritumoural regions of liver metastases. Only the CD8/CD3 TIL ratio demonstrated a positive correlation between intratumoural and peritumoural regions of liver metastases (r = 0.541, p &lt, 0.001). Patients with high intratumoural CD8/CD3 ratios had significantly longer 3-year RFS (59.0% vs. 47.4%, p = 0.035) and 3-year OS rates (83.3% vs. 65.8%, p = 0.007) than those with low intratumoural CD8/CD3 ratios. Multivariate analyses revealed that the intratumoural CD8/CD3 ratio was independently associated with RFS (HR = 0.593, 95% CI = 0.357&ndash, 0.985, p = 0.043) and OS (HR = 0.391, 95% CI = 0.193&ndash, 0.794, p = 0.009). Conclusion: These findings offer a better understanding of the prognostic value of immune cell infiltration on liver oligometastasis from colorectal cancer.

Purpose: The prognostic nutritional index (PNI) has been correlated with long-term outcomes in various cancer patients. However, the relationship between the PNI and long-term outcomes in patients with colorectal cancer liver metastasis (CRLM) who have undergone liver surgery have not been fully investigated. In this study, we aimed to identify the impact of the preoperative PNI on the long-term oncologic outcomes of patients with CRLM who have undergone curative hepatic resection. Methods: A total of 243 CRLM patients who underwent curative hepatic resection for liver metastases in the Sun Yat-sen University Cancer Center between September 1999 and July 2015 were enrolled, and their medical records were analyzed retrospectively. The preoperative PNI was calculated as 10× the serum albumin concentration (g/dL) + 0.005 × the total lymphocyte count (per mm3). The PNI was compared according to the statuses of clinicopathological features. In addition, the regression-free survival (RFS) and overall survival (OS) were analyzed according to the preoperative PNI using univariate and multivariate analyses. Results: The optimal cut-off value of the preoperative PNI was set at 48.5 using the X-tile software. Older patients and those who had undergone synchronous hepatic resection were more likely to belong to the low PNI group (≤48.5) (all P 48.5 was associated with markedly better survival outcomes as an independent factor, both for OS and RFS. Conclusion: For patients with CRLM undergoing curative hepatic resection, preoperative PNI is a simple and efficient indicator (cut-off value=48.5) for preoperative estimation of oncologic outcomes.

Objective: Hepatitis B virus (HBV) infection has been shown to decrease the risk of liver metastasis in patients with non-metastatic colorectal cancer (CRC). However, the prognostic value of HBV infection in long-term survival of patients with colorectal liver-only metastases (CRLM) after liver resection has not yet been evaluated. This study aims to explore the association between HBV infection and survival in CRLM patients. Methods: A total of 289 CRLM patients undergoing liver resection were recruited at our center from September 1999 to August 2015. Patients were divided into an HBV infection group and a non-HBV infection group. Progression-free survival (PFS) and overall survival (OS) related to HBV infection were analyzed using both Kaplan-Meier and multivariate Cox regression methods. Results: HBV infection was found in 12.1 %(35/289) of patients. Of these patients, 31.4 %(11/35) had chronic hepatitis B (CHB), 42.9 % (15/35) were inactive hepatitis B surface antigen (HBsAg) carriers (IC) and 25.7 % (9/35) did not undergo HBV DNA detection. HBV infection was associated with more liver metastases (P = 0.025) and larger-sized liver metastases (P = 0.049). The 3-year OS and PFS rates in the HBV infection group were higher than those in the HBV non-infected group (OS: 75.0 % vs 64.8 %, P = 0.031; PFS: 55.9 % vs 39.6 %, P = 0.034). In multivariate Cox analysis, HBV infection was identified as an independent factor for better 3-year OS (hazard ratio (HR), 0.446; 95 %confidence interval (CI), 0.206-0.966; P = 0.041) but not an independent factor for 3-year PFS. Conclusions: HBV-infected CRLM patients survived longer than non-infected patients. In clinical work, therapeutic regimens and follow-up for HBsAg-positive patients may be different from that for HBsAg-negative patients, even though objective prospective studies are still needed.

Purpose Oligometastatic disease can potentially be cured when an optimal approach is performed. Early recurrence after liver resection is an intractable problem, and the clinical implications remain unknown in colorectal liver oligometastases (CLOM) patients. This study aimed to investigate the clinical characteristics, risk factors, and prognosis related to early recurrence in these patients. Methods A total of 307 consecutive patients with CLOM undergoing curative liver resection were retrospectively reviewed between September 1999 and June 2016. Early recurrence was defined as any recurrence or death from CLOM that occurred within 6 months of liver resection. Results With a median follow-up time of 31.7 months, the 3-year overall survival (OS) and recurrence-free survival rates were 68.7 and 42.5%, respectively. Forty-nine (16.0%) patients developed early recurrence and showed a poorer 3-year OS than those with non-early recurrence (22.3 vs. 75.8%, P 3 cm (OR 2.560; 95% CI 1.290–5.078; P = 0.007) were shown to be risk factors for early recurrence. The salvage liver resection rate for patients with early recurrence was significantly lower than that for patients with later recurrence (4.1 vs. 19.7%, P = 0.010). Conclusions Early recurrence should be investigated in routine clinical practice, even in patients with CLOM after curative liver resection. Detailed preoperative comprehensive measurements might help stratify high-risk patients, and a non-surgical treatment for early recurrence might represent an effective alternative.

Purpose: To date, there is not enough evidence concerning the optimal treatment strategy for early rectal carcinoids, we conducted a meta-analysis in order to determine the feasible local treatment for these selected patients. Methods: We searched the studies from the PubMed, Cochrane database, Medline, Ovid, SpringerLink, PMC and Embase between January 2007 and April 2017. Studies of local surgical excision compared with endoscopic resection for rectal carcinoids less than 20mm without adverse features were included. Data were analyzed by using Stata SE 12.0. Results: Seven studies were included in this meta-analysis, with a total of 1056 patients. The data showed that local surgical excision was associated with higher complete resection rate than that of endoscopic resection (OR 5.837, 95%CI 2.048 to 16.632, P=0.001) but consuming longer procedural time (SMD 1.757, 95% CI 1.263 to 2.251, P=0.000). Additionally, incidences of recurrence and en bloc resection rate were comparable between two kinds of resections. The difference of post-operative complications remained unclear. Conclusions: For rectal carcinoids sized 20mm or smaller without adverse features, endoscopic resection might be an efficient treatment, which achieved a comparable oncological safety as local surgical excision.

Background Although universal testing for mismatch repair deficiency (dMMR) has been recommended to all colorectal cancer (CRC) patients, related evidence for the Chinese population is lacking. Here, we investigated the prevalence and clinicopathological features of dMMR patients in a large Chinese CRC cohort. Methods We included 7,373 CRC patients treated at four Chinese medical centers between August 2010 and September 2016. Patients’ baseline characteristics and pathological features were recorded. The clinicopathological features were compared between patients with MLH1/PMS2 deficiency (dMLH1/PMS2) and MSH2/MSH6 deficiency (dMSH2/MSH6). Results Among the investigated patients, 654 (8.9%) were identified with dMMR CRCs and, of them, 401 (61.3%) were males, with a median age of 55 years (range, 22–87 years); 355 (54.3%) had stage II CRC based on American Joint Committee on Cancer 8th edition. The prevalence of the dMLH1/PMS2 group and the dMSH2/MSH6 group were 51.5% (337/654) and 25.1% (164/654), respectively. Compared with dMSH2/MSH6 patients, those with dMLH1/PMS2 were older (57 vs 52 years, P Conclusions The prevalence of dMMR in Chinese CRC patients was low, especially in the dMLH1/PMS2 group. The clinicopathological features were different between dMMR subgroups.

Background: The overview of the tumor microenvironment on liver oligometastasis from colorectal cancer remains largely unclear. A comprehensive investigation on the immune cell infiltration and its constituent ratio might provide a more accurate and reliable prognostic information for the patients with colorectal liver oligometastasis (CLO) after liver metastasectomy. Methods: A simultaneous detection of immune constituents CD3+, CD8+, Foxp3+ T cells, and α-SMA fibroblast on the liver oligometastasis of 133 patients were conducted by using a five-color immunohistochemical multiplex technique. The immune cells were quantified and tumor-infiltrating lymphocytes (TILs) ratios were subsequently calculated. Correlation analysis was performed using Pearson's correlation. Recurrence-free survival (RFS) and overall survival (OS) for TIL ratios were analyzed using the Kaplan-Meier method and Cox regression models. Results: The number of CD3+, CD8+, and Foxp3+ T cells were significantly fewer in the intratumoral subsection by compared to the peritumoral subsection of metastases. CD3+, CD8+, Foxp3+ T cells, and α-SMA+ fibroblast showed a significantly positive correlation between each other both in the intratumoral and peritumoral subsection of liver metastases. As to the correlation of TIL ratios, only the CD8/CD3 ratio demonstrated a positive correlation in intratumoral and peritumoral metastases (r=0.541, P

Additional file 1: Table S1. Univariate and multivariate Cox proportional hazards regression models for OS.

BackgroundDickkopf 1 (DKK1) is associated with tumor progression. However, whether DKK1 influences the tumor response to programmed cell death protein 1 (PD-1) blockade in colorectal cancers (CRCs) with deficient mismatch repair (dMMR) or microsatellite instability (MSI) has never been clarified.MethodsTumor tissues from 80 patients with dMMR CRC were evaluated for DKK1 expression and immune status via immunohistochemistry. Serum DKK1 was measured in another set of 43 patients who received PD-1 blockade therapy. CT26 cells and dMMR CRC organoids were cocultured with T cells, and CT26-grafted BALB/c mice were also constructed. T-cell cytotoxicity was assessed by apoptosis assays and flow cytometry. The pathway through which DKK1 regulates CD8+ T cells was investigated using RNA sequencing, and chromatin immunoprecipitation and luciferase reporter assays were conducted to determine the downstream transcription factors of DKK1.ResultsElevated DKK1 expression was associated with recurrence and decreased CD8+ T-cell infiltration in dMMR CRCs, and patients with high-serum DKK1 had a poor response to PD-1 blockade. RNA interference or neutralization of DKK1 in CRC cells enhanced CD8+ T-cell cytotoxicity, while DKK1 decreased T-bet expression and activated GSK3β in CD8+ T cells. In addition, E2F1, a downstream transcription factor of GSK3β, directly upregulated T-bet expression. In organoid models, the proportion of apoptotic cells was elevated after individual neutralization of PD-1 or DKK1 and was further increased on combined neutralization of PD-1 and DKK1.ConclusionsDKK1 suppressed the antitumor immune reaction through the GSK3β/E2F1/T-bet axis in CD8+ T cells. Elevated serum DKK1 predicted poor tumor response to PD-1 blockade in dMMR/MSI CRCs, and DKK1 neutralization may restore sensitivity to PD-1 blockade.

Yuxiang Deng,1,* Jianhong Peng,1,* Yujie Zhao,1 Qiaoqi Sui,1 Ruixia Zhao,2 Zhenhai Lu,1 Miaozhen Qiu,3 Junzhong Lin,1 Zhizhong Pan1 1Department of Colorectal Surgery, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, People’s Republic of China; 2Department of Public Health, School of Public Health, Sun Yat-sen University, Guangzhou, People’s Republic of China; 3Department of Medical Oncology, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Sun Yat-sen University Cancer Center, Guangzhou, People’s Republic of China *These authors contributed equally to this work Background: Recent studies have suggested that the lymph node ratio (LNR) is a prognostic indicator for various malignancies. However, LNR has not been evaluated in colorectal liver-only metastasis (CRLM). This study aimed to investigate the prognostic value of LNR in patients with CRLM after curative resection. Patients and methods: We retrospectively investigated the clinicopathologic features of 154 CRLM patients who underwent curative resection between 2005 and 2015. We classified patients into low and high groups based on their LNR by using the X-tile software. Survival curves were plotted through Kaplan–Meier method and compared by log-rank test. Cox proportional hazards analysis was performed to identify the factors associated with recurrence-free survival (RFS) and overall survival (OS). Results: The patients were divided into two groups in which 124 patients were identified as LNR ≤0.33 and 30 patients as LNR >0.33. Compared to low LNR, high LNR was significantly associated with poor 3-year RFS (47.2% vs 16.7%, P=0.001) and OS (72.8% vs 45.3%, P=0.003) rates. Multivariate analysis indicated that the LNR was an independent predictor for 3-year RFS (hazard ratio, 2.124; 95% CI, 1.339–3.368; P=0.001) and OS (HR, 2.287; 95% CI, 1.282–4.079; P=0.005). However, the node (N) stage and lymph node distribution were not significantly associated with the 3-year RFS (P=0.071, P=0.226) or OS (P=0.452, P=0.791) in patients with CRLM. Conclusion: This study demonstrated that LNR was an independent predictor for 3-year RFS and OS in patients with CRLM who underwent curative resection and that its prognostic value was superior to that of N stage and lymph node distribution. Keywords: colorectal cancer, liver metastases, lymph node ratio, N stage, prognosis

Background Although colorectal oligometastases to the liver can potentially be cured with aggressive local ablation, the efficacy of adjuvant chemotherapy (ACT) for such metastasis remains unclear. The present study explored the effects of ACT on patients with colorectal liver oligometastases (CLO) after curative resections and aimed to identify patients who could benefit from ACT. Methods We retrospectively analyzed 264 eligible patients with CLO who underwent curative resection between September 1999 and June 2015. Recurrence-free survival (RFS) and overall survival (OS) were analyzed using the Kaplan–Meier method and log-rank test; prognostic factors were a by Cox regression modeling. Results Among 264 patients, 200 (75.8%) patients received ACT and 64 (24.2%) did not receive ACT. These two groups did not significantly differ in clinicopathologic characteristics, and had comparable 3-year OS and RFS rates (RFS: 42.1% vs. 45.7%, P = 0.588; OS: 69.7% vs. 62.7%, P = 0.446) over a median follow-up duration of 35.5 months, irrespective of preoperative chemotherapy. ACT markedly improved 3-year OS in high-risk patients with Memorial Sloan-Kettering Cancer Center clinical risk scores (MSKCC-CRS) of 3–5 (68.2% vs. 33.8%, P = 0.015), but presented no additional benefit in patients with MSKCC-CRS of 0–2 (72.2% vs. 78.6%, P = 0.834). In multivariate analysis, ACT was independently associated with improved OS in patients with MSKCC-CRS of 3–5. Conclusions ACT might offer a prognostic benefit in high-risk patients with CLOs after curative liver resection, but not in low-risk patients. Therefore, patients’ risk status should be determined before ACT administration to optimize postoperative therapeutic strategies.

The application of skeletonization of the hepatoduodenal ligament (SHDL) in the treatment of gastric cancer is rare. In this study, we reviewed the literature concerning the role of the No.12 lymph node dissection for gastric cancer, in order to evaluate the significance of SHDL in radical gastrectomy. We found that the application of SHDL with dissection of the No.12a, No.12b, and No.12p lymph nodes could improve the prognosis of patients with lymph node metastasis. The incidence of complications would not increase when the surgery was performed by experienced surgeons.