Invasive pit pattern, macronodule and depression are predictive factors of submucosal invasion in colorectal laterally spreading tumours from a Western population

A systematic review and meta-analysis of endoscopic mucosal resection vs endoscopic submucosal dissection for colorectal sessile/non-polypoid lesions

BACKGROUND

Current international guidelines strongly advise endoscopic submucosal dissection (ESD) instead of endoscopic mucosal resection (EMR) for the endoscopic resection of sessile colorectal tumours >20 mm.

AIMS

To compare the safety and efficacy of EMR and ESD for treating large non-invasive colorectal lesions.

MATERIAL AND METHODS

We performed a systematic review using electronic databases (MEDLINE/PubMed, EMBASE, and Cochrane Library) on February 21st, 2021 and a meta-analysis to assess en-bloc and R0 rates, and related adverse events.

RESULTS

Twenty-four studies were included, comparing 3,424 ESD and 5,122 EMR procedures. The en-bloc resection rate was 90.8% in the ESD and 33.0% in the EMR group (p < .001). The R0 resection rate was 85.0% in the ESD and 64.6% in the EMR group (p = .005). The rate of perforation was 5.1% in the ESD and 1.67% in the EMR group (p < .001). The bleeding rate was 4.3% in the ESD and 3.6% in the EMR group (p = .008). The overall need for surgery, including oncologic reasons and complications, was 5.9% in the ESD and 3.1% in the EMR group (p < .001).

CONCLUSIONS

ESD for large non-pedunculated colorectal lesions allows a higher rate of R0 resections than EMR, at the cost of a higher perforation rate and the need for additional surgery.

Circular RNA circ_0065378 upregulates tumor suppressor candidate 1 by competitively binding with miR-4701-5p to alleviate colorectal cancer progression

BACKGROUND AND AIM

Colorectal cancer (CRC), the third most lethal human cancer worldwide, seriously threatens human health and life. Numerous circular RNAs (circRNAs) including circ_PLXNB1 (hsa_circ_0065378) have been confirmed to be dysregulated in CRC by RNA-seq analysis. We aimed to explore the functional role of circ_PLXNB1 in CRC malignant behaviors and clarify its potential molecular mechanism.

METHODS

Gene expression levels of circ_PLXNB1 and miR-4701-5p were determined by quantitative real-time polymerase chain reaction analysis. MTT and Transwell assays were conducted to measure cell proliferation, invasion, and migration. Protein expression of tumor suppressor candidate 1 (TUSC1), E-cadherin and N-cadherin was determined by western blot analysis. Mouse xenograft models were used to investigate the role of circ_PLXNB1 in tumor growth.

RESULTS

The results showed that gene expression of circ_PLXNB1 in CRC tissues was significantly downregulated. Overexpression of circ_PLXNB1 inhibited the malignant behaviors of CRC cells, as manifested by the decrease in cell proliferation, cell invasion, migration, and EMT. Mechanistically, circ_PLXNB1 exerted its functional effects by binding with miR-4701-5p. Moreover, TUSC1 siRNA partially abolished the suppressive effect of the miR-4701-5p inhibitor or circ_PLXNB1 on CRC cell malignant behaviors.

CONCLUSIONS

Circ_PLXNB1 attenuated CRC progression by binding with miR-4701-5p to overexpress TUSC1, indicating that the circ_PLXNB1/miR-4701-5p/TUSC1 axis might be a potential novel molecular target in CRC diagnosis and therapy.

Risk and Time Pattern of Recurrences After Local Endoscopic Resection of T1 Colorectal Cancer: A Meta-analysis

BACKGROUND & AIMS

Growing numbers of patients with T1 CRC are being treated with local endoscopic resection only and as a result, the need for optimization of surveillance strategies for these patients also increases. We aimed to estimate the cumulative incidence and time pattern of CRC recurrences for endoscopically treated patients with T1 CRC.

METHODS

Using a systematic literature search in PubMed, EMBASE, Web of Science and Cochrane Library (from inception till 15 May 2020), we identified and extracted data from studies describing the cumulative incidence of local or distant CRC recurrence for patients with T1 CRC treated with local endoscopic resection only. Pooled estimates were calculated using mixed-effect logistic regression models.

RESULTS

Seventy-one studies with 5167 unique, endoscopically treated patients with T1 CRC were included. The pooled cumulative incidence of any CRC recurrence was 3.3% (209 events; 95% CI, 2.6%-4.3%; I² = 54.9%), with local and distant recurrences being found at comparable rates (pooled incidences 1.9% and 1.6%, respectively). CRC-related mortality was observed in 42 out of 2519 patients (35 studies; pooled incidence 1.7%, 95% CI, 1.2%-2.2%; I² = 0%), and the CRC-related mortality rate among patients with recurrence was 40.8% (42/103 patients). The vast majority of recurrences (95.6%) occurred within 72 months of follow-up. Pooled incidences of any CRC recurrence were 7.0% for high-risk T1 CRCs (28 studies; 95% CI, 4.9%-9.9%; I² = 48.1%) and 0.7% (36 studies; 95% CI, 0.4%-1.2%; I² = 0%) for low-risk T1 CRCs.

CONCLUSIONS

Our meta-analysis provides quantitative outcome measures which are relevant to guidelines on surveillance after local endoscopic resection of T1 CRC.

Is underwater endoscopic mucosal resection of colon polyps superior to conventional techniques? A network analysis of endoscopic mucosal resection and submucosal dissection

Background and study aims  Evidence from recent trials comparing conventional endoscopic mucosal resection (EMR) to underwater EMR (UEMR) have matured. However, studies comparing UEMR to endoscopic submucosal dissection (ESD) are lacking. Hence, we sought to conduct a comprehensive network meta-analysis to compare the efficacy of UEMR, ESD, and EMR. Methods  Embase and Medline databases were searched from inception to December 2020 for articles comparing UEMR with EMR and ESD. Outcomes of interest included rates of en bloc and complete polyp resection, risk of perforation and bleeding, and local recurrence. A network meta-analysis comparing all three approaches was conducted. In addition, a conventional comparative meta-analysis comparing UEMR to EMR was performed. Analysis was stratified according to polyp sizes (< 10 mm, ≥ 10 mm, and ≥ 20 mm). Results  Twenty-two articles were included in this study. For polyps ≥ 10 mm, UEMR was inferior to ESD in achieving en bloc resection ( P  = 0.02). However, UEMR had shorter operating time for polyps ≥ 10 mm ( P  < 0.001), and ≥20 mm ( P  = 0.019) with reduced perforation risk for polyps ≥ 10 mm ( P  = 0.05) compared to ESD. In addition, en bloc resection rates were similar between UEMR and EMR, although UEMR had reduced recurrence for polyps ≥ 10 mm ( P  = 0.013) and ≥ 20 mm ( P  = 0.014). UEMR also had shorter mean operating than EMR for polyps ≥ 10 mm ( P  < 0.001) and ≥ 20 mm ( P  < 0.001). Risk of bleeding and perforation with UEMR and EMR were similar for polyp of all sizes. Conclusions  UEMR has demonstrated technical and oncological outcomes comparable to ESD and EMR, along with a desirable safety profile. UEMR appears to be a safe and effective alternative to conventional methods for resection of polyps ≥ 10 mm.

Blue laser imaging combined with JNET (Japan NBI Expert Team) classification for pathological prediction of colorectal laterally spreading tumors

BACKGROUND

Blue laser imaging (BLI) can provide useful information on colorectal laterally spreading tumors (LSTs) by visualizing the surface and vessel patterns in detail. The present research aimed to evaluate the diagnostic performance of BLI-combined JNET (Japan NBI Expert Team) classification for identifying LSTs.

METHODS

This retrospective, multicenter study included 172 LSTs consisted of 6 hyperplastic polyps/sessile serrated polyps, 94 low-grade dysplasias (LGD), 60 high-grade dysplasias (HGD), 6 superficial submucosal invasive (m-SMs) carcinomas, and 4 deep submucosal invasive carcinomas. The relationship between the JNET classification and the histologic findings of these lesions were then analyzed.

RESULTS

For all LSTs, non-experts and experts had a 79.7% and 90.7% accuracy for Type 2A (P = 0.004), a sensitivity of 94.7% and 96.8% (P = 0.718), and a specificity of 61.5% and 83.3% (P = 0.002) for prediction of LGD, respectively. The results also demonstrated 80.8% and 91.3% accuracy for Type 2B (P = 0.005), a sensitivity of 65.2% and 83.3% (P = 0.017), and a specificity of 90.6% and 96.2% (P = 0.097) for predicting HGD or m-SMs. For LST-granular (LST-G) lesions, Type 2A in experts had higher specificity (65.6% vs. 83.6%, P = 0.022) and accuracy (81.8% vs. 91.2%, P = 0.022). Type 2B in experts only had higher accuracy (82.5% vs. 92.0%, P = 0.019). However, no significant differences were noted for any comparisons between non-experts and experts for LST-non-granular (LST-NG) lesions.

CONCLUSIONS

BLI combined with JNET classification was an effective method for the precise prediction of pathological diagnosis in patients with LSTs. Diagnostic performance of JNET classification by experts was better than that by non-experts for all examined LST or LST-G lesions when delineating between Type 2A and 2B, but there was no difference for the identification of LST-NG lesions by these two groups.

Indications and outcomes of endoscopic resection for non-pedunculated colorectal lesions: A narrative review

In the last years, endoscopic techniques gained a crucial role in the treatment of colorectal flat lesions. At the same time, the importance of a reliable assessment of such lesions to predict the malignancy and the depth of invasion of the colonic wall emerged. The current unsolved dilemma about the endoscopic excision techniques concerns the necessity of a reliable submucosal invasive cancer assessment system that can stratify the risk of the post-procedural need for surgery. Accordingly, this narrative literature review aims to compare the available diagnostic strategies in predicting malignancy and to give a guide about the best techniques to employ. We performed a literature search using electronic databases (MEDLINE/PubMed, EMBASE, and Cochrane Library). We collected all articles about endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD) registering the outcomes. Moreover, we analyzed all meta-analyses comparing EMR vs ESD outcomes for colorectal sessile or non-polypoid lesions of any size, preoperatively estimated as non-invasive. Seven meta-analysis studies, mainly Eastern, were included in the analysis comparing 124 studies and overall 22954 patients who underwent EMR and ESD procedures. Of these, eighty-two were retrospective, twenty-four perspective, nine case-control, and six cohorts, while three were randomized clinical trials. A total of 18118 EMR and 10379 ESD were completed for a whole of 28497 colorectal sessile or non-polypoid lesions > 5-10 mm in size. In conclusion, it is crucial to enhance the preoperative diagnostic workup, especially in deciding the most suitable endoscopic method for radical resection of flat colorectal lesions at risk of underlying malignancy. Additionally, the ESD necessitates further improvement because of the excessively time-consuming as well as the intraprocedural technical hindrances and related complications. We found a higher rate of en bloc resections and R0 for ESD than EMR for non-pedunculated colorectal lesions. Nevertheless, despite the lower local recurrence rates, ESD had greater perforation rates and needed lengthier procedural times. The prevailing risk for additional surgery in ESD rather than EMR for complications or oncologic reasons is still uncertain.

Endoscopic submucosal dissection vs endoscopic mucosal resection for colorectal polyps: A meta-analysis and meta-regression with single arm analysis

BACKGROUND

Endoscopic submucosal dissection (ESD) has shown to be effective in management of colorectal neoplasm in the Asian countries, while its implementation in Western countries where endoscopic mucosal resection (EMR) is preferred is still debatable.

AIM

To compare the surgical, histological, and oncological outcomes between ESD and EMR in the treatment of colorectal polyps, with subgroup analysis comparing the efficacy of ESD and EMR between Japan and the rest of the world.

METHODS

Embase and Medline databases were searched from inception to October 2020 in accordance with PRISMA guidelines for studies comparing en bloc, complete resection, margin involvement, resection time, need for additional surgery, complications, and recurrence rate of ESD with EMR.

RESULTS

Of 281344 colorectal polyps from 21 studies were included. When compared to EMR, the pooled analysis revealed ESD was associated with higher en bloc and complete resection rate, and lower lateral margin involvement and recurrence. ESD led to increased procedural time, need for additional surgery, and perforation risk. No significant difference in bleeding risk was found between the two groups. Meta-regression analysis suggested only right colonic polyps correlated with an increased perforation risk in ESD. Confounders including polyp size and invasion depth did not significantly influence the en bloc and complete resection rate, bleeding risk and recurrence. In subgroup analysis, Japan performed better than the rest of the world in both ESD and EMR with perforation risk of 4% and 0.0002%, respectively, as compared to perforation risk of 8% and 1%, respectively, in reports coming from rest of the world.

CONCLUSION

ESD resulted in better resection outcomes and lower recurrence compared to EMR. With appropriate training, ESD is preferred over EMR as the first-line therapy for resection of colorectal polyps, without restricting to lesions greater than 20 mm and those with high suspicion of submucosal invasion.

Detection of Mice Colorectal Tumors by Endoluminal Ultrasound Biomicroscopic Images and Quantification of Image Augmented Gray Values Following Injection of VEGFR-2 Targeted Contrast Agent

RATIONALE AND OBJECTIVES

Ultrasound biomicroscopy (UBM) is a noninvasive imaging technique that can be applied in detecting colonic tumors and, once associated with an ultrasound contrast agent (UCA), can identify the molecular expression of cancer-related biomarkers, such as the vascular endothelial growth factor receptor 2 (VEGFR-2). The present work aimed to detect colonic tumors and quantify augmented gray values of endoluminal UBM (eUBM) images from colonic tumors following the injection of VEGFR-2 targeted UCA (VEGFR2-UCA) into a mouse model of colorectal cancer.

MATERIAL AND METHODS

A 40 MHz miniprobe catheter inserted through the biopsy channel of a pediatric flexible bronchofiberscope was used to obtain colonoscopic and B-mode eUBM images simultaneously. Seventeen tumor-bearing mice had their colons inspected and six of them were subjected to a VEGFR2-UCA injection to predict VEGFR-2 expression.

RESULTS

All animals developed distal colon tumors and eUBM was able to detect all of them and also to characterize the tumors, with 71.4% being in situ lesions and 28.6% being tumors invading the mucosa + muscularis mucosae + submucosa layers, as confirmed by histopathology. After VEGFR2-UCA injection, gray values from the eUBM tumoral images increased significantly (p < 0.01). Tumor sites with increased eUBM image gray values corresponded to areas with increased VEGFR-2 expression, as confirmed by immunohistochemistry.

CONCLUSION

The results confirm eUBM as a powerful noninvasive and real-time tool for detecting colon tumor and its invasiveness and once associated with VEGFR2-UCA may become a tool for the detection of VEGFR-2 expression in colonic tumors.

Fecal Enterotoxigenic Bacteroides fragilis-Peptostreptococcus stomatis-Parvimonas micra Biomarker for Noninvasive Diagnosis and Prognosis of Colorectal Laterally Spreading Tumor

Objective

Up to now, non-invasive diagnosis of laterally spreading tumor (LST) and prediction of adenoma recurrence after endoscopic resection of LSTs is inevitable. This study aimed to identify a microbial signature with clinical significance of diagnosing LSTs and predicting adenoma recurrence after LSTs colectomy.

Methods

We performed 16S rRNA sequencing in 24 mucosal samples, including 5 healthy controls (HC), 8 colorectal adenoma (CRA) patients, and 11 LST patients. The differentiating microbiota in fecal samples was quantified by qPCR in 475 cases with 113 HC, 208 CRA patients, 109 LST patients, and 45 colorectal cancer (CRC) patients. We identified differentially abundant taxa among cases and controls using linear discriminant analysis effect size analysis. ROC curve was used to evaluate diagnostic values of the bacterial candidates. Pairwise comparison of AUCs was performed by using the Delong's test. The Mantel-Haenszel hazard models were performed to determine the effects of microbial compositions on recurrence free survival.

Results

The microbial dysbiosis of LST was characterized by relative high abundance of the genus Lactobacillus-Streptococcus and the species enterotoxigenic Bacteroides fragilis (ETBF)-Peptostreptococcus stomatis (P. stomatis)-Parvimonas micra (P. micra). The abundance of ETBF, P. stomatis, and P. micra were steadily increasing in LST and CRC groups. P. stomatis behaved stronger value on diagnosing LST than the other two bacteria (AUC 0.887, 95% CI 0.842-0.931). The combination of P. stomatis, P. micra, and ETBF (AUC 0.922, 95% CI 0.887-0.958) revealed strongest diagnostic power with 88.7% sensitivity and 81.4% specificity. ETBF, P. stomatis, and P. micra were associated with malignant LST (P_P.stomatis = 0.0015, P_P.micra = 0.0255, P_ETBF = 0.0169) and the abundance of IL-6. The high abundance of P. stomatis was related to the adenoma recurrence after LST resection (HR = 3.88, P = 0.008).

Conclusions

Fecal microbiome signature (ETBF-P. stomatis-P. micra) can diagnose LSTs with high accuracy. ETBF, P. stomatis, and P. micra were related to malignant LST and P. stomatis exhibited high predictive value on the adenoma recurrence after resection of LSTs. The fecal microbiome signature of LST may provide a noninvasive alternative to early detect LST and predict the adenoma recurrence risk after resections of LSTs.

Pathological Analysis and Endoscopic Characteristics of Colorectal Laterally Spreading Tumors

Objective

This study aims to analyze the endoscopic and pathological characteristics of colorectal laterally spreading tumors (LSTs) to assist malignant risk stratification to inform selection of the appropriate treatment strategy.

Methods

Patients with colorectal LST were selected as retrospective study objects. Characteristics, including endoscopic findings and the most common site of LSTs of different diameters and histological types, were analyzed. The risk factors for malignancy in colorectal LST were explored by multivariate logistic regression analysis.

Results

LSTs with diameters of ≥20 mm were found mainly in the rectum and mainly with granular-mixed (G-M) morphology (36% and 44.6%, respectively; p < 0.05), while LSTs with diameters of <20 mm were found mainly in the ascending colon and mainly with granular-homogenous (G-H) morphology (40.9% and 46.2%, respectively; p < 0.05). Adenoma was the main histological type in patients with tumors of all diameters. However, the cancerization rate of LSTs was 31% in patients with tumor diameter ≥20 mm, while there was no invasive cancer in patients with tumor diameter < 20 mm. In the low-grade dysphasia (adenoma) group, most of the lesions were located in the ascending colon and most had the morphology LST-G-H (35.8% and 39.2%, respectively; p < 0.05). In the cancerization group, most of the lesions were located in the rectum, with the morphology LST-G-M (51.6% and 67.2%, respectively; p < 0.05), and the diameter was larger than that of the adenoma group (33.84 ± 17.99 mm vs 21.68 ± 8.99 mm).

Conclusion

The rectum was the most common site for an LST with a diameter ≥20 mm and cancerization, of which the morphology was mainly LST-G-M (endoscopic submucosal dissection is the preferred treatment for this type of LST). LST malignancy was found to be correlated with lesion diameter, location, and morphological appearance.

Treatment policy for colonic laterally spreading tumors based on each clinicopathologic feature of 4 subtypes: actual status of pseudo-depressed type

BACKGROUND AND AIMS

Laterally spreading tumors (LSTs) are originally classified into 4 subtypes. Pseudo-depressed nongranular types (LSTs-NG-PD) are gaining attention because of their high malignancy potential. Previous studies discussed the classification of nongranular (LST-NG) and granular types (LST-G); however, the actual condition or indication for endoscopic treatment of LSTs-NG-PD remains unclear. We aimed to compare the submucosal invasion pattern of LSTs-NG-PD with the other 3 subtypes.

METHODS

A total of 22,987 colonic neoplasms including 2822 LSTs were resected endoscopically or surgically at Showa University Northern Yokohama Hospital. In these LSTs, 322 (11.4%) were submucosal invasive carcinomas. We retrospectively evaluated the clinicopathologic features of LSTs divided into 4 subtypes. In 267 LSTs resected en bloc, their submucosal invasion site was further evaluated.

RESULTS

The frequency of LSTs in all colonic neoplasms was significantly higher in women (14.9%) than in men (11.0%). Rates of submucosal invasive carcinoma were .8% in the granular homogenous type (LSTs-G-H), 15.2% in the granular nodular mixed type (LSTs-G-M), 8.0% in the nongranular flat elevated type (LSTs-NG-F), and 42.5% in LSTs-NG-PD. Tumor size was associated with submucosal invasion rate in LSTs-NG-F and LSTs-NG-PD (P < .001). The multifocal invasion rate of LSTs-NG-PD (46.9%) was significantly higher than that of LSTs-G-M (7.9%) or LSTs-NG-F (11.8%). In LSTs-NG-PD, the invasion was significantly deeper (≥1000 μm) if observed in 1 site.

CONCLUSIONS

For LSTs-G-M and LSTs-NG-F that may have invaded the submucosa, en bloc resection could be considered. Considering that LSTs-NG-PD had a higher submucosal invasion rate, more multifocal invasive nature, and deeper invasion tendency, regardless if invasion was only observed in 1 site, than LSTs-NG-F, we should endoscopically distinguish LSTs-NG-PD from LSTs-NG-F and strictly adopt en bloc resection by endoscopic submucosal dissection or surgery for LSTs-NG-PD. (Clinical trial registration number: UMIN 000020261.).

Improving assessment and management of large non-pedunculated colorectal lesions in a Western center over 10 years: lessons learned and clinical impact

Background and study aims  Outcomes of endoscopic assessment and management of large colorectal (CR) non-pedunculated lesions (LNPLs) are still under evaluation, especially in Western settings. We analyzed the clinical impact of changes in LNPL management over the last decade in a European center. Patients and methods  All consecutive LNPLs ≥ 20 mm endoscopically assessed (2008-2019) were retrospectively included. Lesion, patient, and resection characteristics were compared among clinically relevant subgroups. Multivariate logistic regression (for predictors of submucosal invasion [SMI] and recurrence), Kaplan-Meier curves and ROC curves (for temporal cut-offs in trends analyses) were used. Results  A total of 395 LNPLs were included (30 mm [range 20-40]; SMI = 9.6 %; primary endoscopic resection [ER] = 88.4 %). Pseudo-depression and JNET classification independently predicted SMI beyond single morphologies/location. After complete ER, involvement of ileocecal valve/dentate line, piece-meal resection and high-grade dysplasia independently predicted recurrence. Rates of 5-year recurrence-free, surgery-free and cancer-free survival were 77.5 %, 98.6 % and 100 %, respectively, with 93.8 % recurrences endoscopically managed and no death attributable to ER or CR cancer (versus 3.4 % primary surgery mortality). ROC curves identified the period ≥ 2015 (following Endoscopic Submucosal Dissection [ESD] introduction and education on pre-resective lesion assessment) as associated with improved lesions' characterization, increased en-bloc resection of SMI lesions (87.5 % vs 37.5 %; p = 0.0455), reduced primary surgery (7.5 % vs 16.7 %; p = 0.0072), surgical referral of benign lesions (5.1 % vs 14.8 %; p = 0.0019), and recurrences. Conclusions  ESD introduction and educational interventions allowed ER of more complex lesions, offset by increased complementary surgery for complications or intrinsic histological risk. Nevertheless, overall, they have reduced surgery demand and increased appropriateness and safety of LNPL management in our center.

The Coexistence of Colorectal Polyps in the Right Colon Increases the Malignant Risk of Laterally Spreading Tumors

Background

The coexistence of colorectal polyps with laterally spreading tumors (LSTs) is commonly observed during colonoscopy. However, there are rare studies that assess the malignant risks for LSTs with colorectal polyps, which might largely contribute to further strategies of treatment and follow-up plans in LSTs.

Methods

We conducted a retrospective cohort study that enrolled 206 patients with LSTs in the Endoscopy Center and Endoscopy Research Institute, Renji Hospital, Shanghai Jiao Tong University, China. The subjects with LSTs were divided into two groups: the nonpolyp group with 89 patients and the polyp group with 117 patients. Binary logistic regression was used to identify the independent predictors of outcomes of interest.

Results

The risk of the polyps' coexistence phenomenon increased in males compared with females (OR = 2.138, p = 0.047), especially in those between 50 and 75 years old (OR = 7.074, p = 0.036). Tumor size (3–4 cm), LSTs with tubulovillous types, and history of polyps statistically increased the risk of the polyp coexistence phenomenon (OR = 5.768, p = 0.003; OR = 36.345, p = 0.024; OR = 13.245, p < 0.0001, respectively). LST-NG-PD (OR = 20.982, p = 0.017) and LSTs ≥ 5 cm (OR = 37.604, p = 0.038) notably increased the malignant risk of LSTs. When the simultaneous polyps are located in the right colon, the risk of malignant LSTs (OR = 58.540, p = 0.013) positively increased.

Conclusion

The simultaneous colorectal polyps in the right colon were the most important risk factor to predict the malignant risk of LSTs.