Functional annotation with expression validation identifies novel metastasis-relevant genes from post-GWAS risk loci in sporadic colorectal carcinomas

BACKGROUND

Colorectal cancer (CRC) is the third highest incidence cancer and is the leading cause of cancer mortality worldwide. Metastasis to distal organ is the major cause of cancer mortality. However, the underlying genetic factors are unclear. This study aimed to identify metastasis-relevant genes and pathways for better management of metastasis-prone patients.

METHODS

A case-case genome-wide association study comprising 2677 sporadic Chinese CRC cases (1282 metastasis-positive vs 1395 metastasis-negative) was performed using the Human SNP6 microarray platform and analysed with the correlation/trend test based on the additive model. SNP variants with association testing -log10 p value ≥5 were imported into Functional Mapping and Annotation (FUMA) for functional annotation.

RESULTS

Glycolysis was uncovered as the top hallmark gene set. Transcripts from two of the five genes profiled, hematopoietic substrate 1 associated protein X 1 (HAX1) and hyaluronan-mediatedmotility receptor (HMMR), were significantly upregulated in the metastasis-positive tumours. In contrast to disease-risk variants, HAX1 appeared to act synergistically with HMMR in significantly impacting metastasis-free survival. Examining the subtype datasets with FUMA and Ingenuity Pathway Analysis (IPA) identified distinct pathways demonstrating sexual dimorphism in CRC metastasis.

CONCLUSIONS

Combining genome-wide association testing with in silico functional annotation and wet-bench validation identified metastasis-relevant genes that could serve as features to develop subtype-specific metastasis-risk signatures for tailored management of patients with stage I-III CRC.

[Research progress in stent associated respiratory tract infection]

Airway stents are commonly used to treat patients with central airway obstruction, but several complications have been identified, including mucus plugging, granulation tissue, stent migration, and infection. Stent associated respiratory tract infection (SARTI) has often been neglected by the practicing clinicians. Therefore, we reviewed the available current literatures on the diagnosis and management of stent associated respiratory tract infection.

Abstract 4119: Anti-KRAS antibody aggregates KRAS in the cytoplasm of live ex vivo cultured human colorectal adenocarcinoma cells and prevents its trafficking to the plasma membrane

Worldwide, colorectal cancer (CRC) is the third highest incidence cancer and a leading cause of cancer mortality. Metastasis to distal organ is the major cause of cancer mortality. However, chemotherapeutic treatment of metastatic CRC has a dismayed success rate of less than 30%. Patients who are resistant to chemotherapy and who are KRAS wildtype are sometimes offered anti-EGFR as a second line therapy. Nevertheless, only about ½ of these patients respond and those who do inevitably develop resistance within months due to selection for downstream KRAS mutations. Moreover, most (80%) sporadic CRCs are microsatellite-stable and are refractory to immune checkpoint blockade therapy. Hence, there is an unmet need to identify novel therapeutics for CRC. KRAS is a gatekeeper gene in colorectal tumorigenesis but is ‘undruggable’ due to its structure not being easily amenable to inhibitor docking. Focus has been diverted to develop small molecule inhibitors for its downstream effectors such as ERK/MAPK and AKT. Despite intense research efforts for the past few decades, however, no small molecule inhibitor has been in clinical use for CRC. Recently developed Sotorasib inhibitor specific for KRAS G12C mutations (rare in CRC) is not effective for CRC. Antibodies have high affinity to their target proteins without having to bind to specific pocket and are fully human in nature and hence less toxic. Antibody targeting KRAS itself is thus an attractive alternative. We developed a transient ex vivo patient-derived matched mucosa-tumor primary culture to assess whether anti-KRAS antibody can be internalized to bind and inactivate KRAS. We showed that anti-KRAS antibody can enter live matched mucosa-tumor cells and specifically aggregate KRAS in the cytoplasm, thus hindering its trafficking to the inner plasma membrane. The mis-localization of KRAS reduces KRAS dwelling time at the site where it tethers to activate downstream effectors. We previously showed that expression of SOX9 was KRAS-mutation-dependent and possibly a better effector than ERK in CRC. In the present study, we showed that anti-KRAS antibody treated tumor cells have less intense SOX9 cytoplasmic and nuclear staining compared to untreated cells suggesting down-regulation of KRAS signaling. Our results demonstrated that anti-KRAS antibody can be internalized and specifically inhibits KRAS function in live tumor cells. With an efficient intracellular antibody delivery system, this can be further developed as combinatorial therapeutics for CRC and other KRAS-driven cancers.

Citation Format: Peh Yean Cheah, Kuen Kuen Lam, Yee Syuen Low, Michelle Lo, Michelle Wong, Choong Leong Tang, Emile Tan, Aik Yong Chok, Issac Seow En, Siew Heng Wong. Anti-KRAS antibody aggregates KRAS in the cytoplasm of live ex vivo cultured human colorectal adenocarcinoma cells and prevents its trafficking to the plasma membrane. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4119.

KRAS-specific antibody binds to KRAS protein inside colorectal adenocarcinoma cells and inhibits its localization to the plasma membrane

Colorectal cancer (CRC) is the third highest incidence cancer and a leading cause of cancer mortality worldwide. To date, chemotherapeutic treatment of advanced CRC that has metastasized has a dismayed success rate of less than 30%. Further, most (80%) sporadic CRCs are microsatellite-stable and are refractory to immune checkpoint blockade therapy. KRAS is a gatekeeper gene in colorectal tumorigenesis. Nevertheless, KRAS is ‘undruggable’ due to its structure. Thus, focus has been diverted to develop small molecule inhibitors for its downstream effector such as ERK/MAPK. Despite intense research efforts for the past few decades, no small molecule inhibitor has been in clinical use for CRC. Antibody targeting KRAS itself is an attractive alternative. We developed a transient ex vivo patient-derived matched mucosa-tumor primary culture to assess whether anti-KRAS antibody can be internalized to bind and inactivate KRAS. We showed that anti-KRAS antibody can enter live mucosa-tumor cells and specifically aggregate KRAS in the cytoplasm, thus hindering its translocation to the inner plasma membrane. The mis-localization of KRAS reduces KRAS dwelling time at the site where it tethers to activate downstream effectors. We previously showed that expression of SOX9 was KRAS-mutation-dependent and possibly a better effector than ERK in CRC. Herein, we showed that anti-KRAS antibody treated tumor cells have less intense SOX9 cytoplasmic and nuclear staining compared to untreated cells. Our results demonstrated that internalized anti-KRAS antibody inhibits KRAS function in tumor. With an efficient intracellular antibody delivery system, this can be further developed as combinatorial therapeutics for CRC and other KRAS-driven cancers.

[A survey on the practice of bronchoscopy in county-level hospitals of China]

Objective: To investigate the bronchoscopy resource allocation and technology application in county-level hospitals in China. Methods: A cross-sectional survey was conducted. In 2021, 12 provinces were sampled from all provinces in China according to the regional Gross Domestic Product (GDP) and the number of counties, in which a total of 291 county-level hospitals were randomly enrolled. Two county-level hospitals which carried out bronchoscopy technology in each province were randomly sampled to investigate the status of bronchoscopy resources, technical application, decontamination and anesthesia by using questionnaires. Independent sample t test or two related sample nonparametric test were used for comparison between groups. Spearman correlation analysis was used to explore the correlation. Bilateral P<0.05 was considered statistically significant. Results: According to the sampling results, it was estimated that in the county-level hospitals, the proportion of those performing bronchoscopy was 11.4% (9.9%, 13.8%), which was significantly correlated with the population in the province (r=0.64, P=0.025) and the regional GDP (r=0.65, P=0.025).The 24 county-level hospitals interviewed were equipped with (1.6±1.0) bronchoscopes on average, and the number of hospitals with electronic bronchoscopes and fiberoptic bronchoscopes was 22 (91.7%) and 6 (25.0%), respectively. Six (25.0%) hospitals performed bronchoscopy every working day. Twelve (50.0%) hospitals had relatively permanent physicians and nurses. All operating doctors had received special training. There was a significant increase in the number of bronchoscopy cases per hospital in 2020 compared to 2019 [140(70, 335) vs. 100(29, 254), P=0.001]. All hospitals used standard cleaning and sterilization workbenches, cleaning agents and disinfectants. Surface anesthesia was available in 24 hospitals, and bronchoscopy techniques under sedation and analgesia were performed in 10 (41.7%) hospitals. Atropine was still used to prevent airway secretions in 2 (8.3%) hospitals,although not recommended by guidelines. Conclusions: There was a large gap between the current status of bronchoscopy technology in county-level hospitals and the standards of the National Health Commission, together with regional disparities. Bronchoscopist training in the standardization and the decontamination work met the requirements. In some hospitals, the use of complementary medicines was not standardized or the sedatives were not given routinely according to the guidelines. We should promote the popularization and standardization of bronchoscopy technology, and strengthen the allocation of related resources in China's county hospitals.

Abstract 6192: ERK/AKT pathways may be the wrong effectors for KRAS signaling inhibition in colorectal cancers

Colorectal cancer (CRC) is the third highest incident cancer worldwide and a major cause of cancer death. KRAS protein gain-of-function point mutations play major roles in colorectal tumorigenesis. However, direct inhibition of KRAS is challenging as its protein structure is inadmissible to inhibitor docking. Efforts have been diverted to inhibit downstream RAF/MEK/ERK and PI3K/Akt signaling. Nevertheless, none of these inhibitors has progressed to clinical use in CRC despite extensive trials over the past few decades. We examined levels of phospho-ERK1/2(T202/Y204) and phospho-Akt1/2/3(S473) in human colorectal tumor and matched mucosa at least 10 cm away with quantitative near infrared western blot and immunofluorescence imaging. Surprisingly, 75.5% (25/33) of tumors has lower or equivalent phospho-ERK1/2 and 96.9% (31/32) of tumors has lower phospho-AKT1/2/3 compared to matched mucosa, irrespective of KRAS mutation status and tumor stage. In contrast, we discovered KRAS-dependent SOX9 upregulation in 28 of the 31 (90.3%) tumors. CPTAC phosphoproteomics data similarly showed significantly lower phospho-ERK1/2 levels in tumor compared to matched mucosa. Analysis of transcriptome data from TCGA and GEO series GSE95132 also showed no activation of RAF/MEK/ERK signaling in CRC tumors. These data indicate that the pursue of targeted therapy inhibiting RAF/MEK/ERK and PI3K/Akt signaling is unlikely to be effective in sporadic CRC and possibly harmful as phospho-ERK1/2 are highly expressed in the matched mucosa suggesting a role in normal colonic homeostasis. The widespread use of RAF/MEK/ERK or PI3K/Akt signaling downregulation as a biomarker in drug testing on CRC cell lines needs to be re-evaluated. The data suggest further that SOX9 could be an alternative effector and biomarker of KRAS signaling.

Citation Format: Peh Yean Cheah, Kuen Kuen Lam, Choong Leong Tang, Emile Tan, Siew Heng Wong. ERK/AKT pathways may be the wrong effectors for KRAS signaling inhibition in colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6192.

KRAS mutation-independent downregulation of MAPK/PI3K signaling in colorectal cancer

KRAS is a gatekeeper gene in human colorectal tumorigenesis. KRAS is ‘undruggable’; hence, efforts have been diverted to inhibit downstream RAF/MEK/ERK and PI3K/Akt signaling. Nevertheless, none of these inhibitors has progressed to clinical use despite extensive trials. We examined levels of phospho‐ERK1/2(T202/Y204) and phospho‐Akt1/2/3(S473) in human colorectal tumor compared to matched mucosa with semi‐quantitative near‐infrared western blot and confocal fluorescence immunohistochemistry imaging. Surprisingly, 75.5% (25/33) of tumors had lower or equivalent phospho‐ERK1/2 and 96.9% (31/32) of tumors had lower phospho‐Akt1/2/3 compared to matched mucosa, irrespective of KRAS mutation status. In contrast, we discovered KRAS‐dependent SOX9 upregulation in 28 of the 31 (90.3%) tumors. These observations were substantiated by analysis of the public domain transcriptomics The Cancer Genome Atlas (TCGA) and NCBI Gene Expression Omnibus (GEO) datasets and proteomics Clinical Proteomic Tumor Analysis Consortium (CPTAC) dataset. These data suggest that RAF/MEK/ERK and PI3K/Akt signaling are unlikely to be activated in most human colorectal cancer.

A prognostic score predicting survival following emergency surgery in patients with metastatic colorectal cancer

BACKGROUND

Survival of patients with metastatic colorectal cancer (mCRC) varies. We aim to develop a prognostic score for mCRC after emergency surgery to guide treatment decisions.

METHODS

Newly diagnosed mCRC patients who presented with primary tumor-related complications and underwent emergency surgery between January 1999 and December 2013 were included. Univariate and multivariate Cox regression analyses were performed to identify covariates significantly associated with the time to death following surgery. A survival score was derived using the Cox regression equation.

RESULTS

The study cohort comprised 248 patients. Median patient age was 66 ± 13 years. Primary tumor was located in the left colon and rectum in 211 patients (85.1%) while 37 patients (14.9%) had primaries in the right colon. Liver, lung, and peritoneal metastases occurred in 161 patients (64.9%), 59 patients (23.8%), and 96 patients (38.7%), respectively. Majority of patients presented with either obstruction (174 patients, 70.1%) or perforation (52 patients, 21%). On multivariate analysis, age of 60 years or older (p = 0.007), carcinoembryonic antigen levels greater than 45 ng/ml (p = 0.022), presence of liver metastases (p = 0.024), and peritoneal carcinomatosis (p < 0.001) were found to be significantly associated with overall survival. A simplified score was derived with good survivors (score 0-2), moderate survivors (score 3-4), and poor survivors (score 5 and above) experiencing median survival of 7, 14, and 23 months, respectively (p < 0.001).

CONCLUSION

The management of mCRC presenting with an emergency is challenging. A prognostic score that estimates survival after emergency surgery may aid clinical decision-making.

Abstract 2829: Identifying germline variants for metastatic risk assessment in sporadic colorectal carcinomas

Colorectal carcinoma (CRC) is the third highest incidence cancer and leading cause of cancer mortality worldwide. Metastasis to distal organ is the major cause of cancer mortality. This trend is expected to be exacerbated by an aging population in the developed world. Genetic predisposition plays a greater role in disease progression than disease etiology in sporadic CRC. However, the underlying genetic factors for metastasis are currently unclear. We identified germline single nucleotide polymorphism (SNP) variants contributing to metastasis risk from a case-case (metastasis-positive vs metastasis-negative) genome-wide association study (GWAS) comprising 3,000 sporadic Chinese CRC cases with definitive metastasis status. Metastasis-positive case is defined as one with distal-organ involvement attributable to primary CRC; metastasis-negative case is defined as metastasis-free with 5 years or more follow-up. By interrogating summarized SNP statistics from the case-case GWAS using the Functional Mapping and Annotation (FUMA) software, we identified 5 genomic risk loci and 74 disease-relevant genes based on gene set enrichment analysis and the Molecular Signatures Database. These genes are in various pathways implicated in different metastasis steps, from epithelial-mesenchymal transition (EMT) to implantation at distal organs. They are different from the risk variants identified by case-control GWAS for disease occurrence. We will expression-profile 250 metastasis-positive vs metastasis negative cases from the GWAS panel to validate the bioinformatics analysis by quantitative real-time PCR. We will focus first on the five genes implicated in glycolysis as this is a biochemical fingerprint of malignant cells that represents one of the ‘hallmarks of cancer'. Expression profile of these genes will be validated in a second independent panel. Kaplan Meier survival analysis as function of the median expression value will be performed to assess prognostic value of these genes. The ultimate goal is to improve metastasis risk assessment for secondary prevention to reduce cancer mortality and morbidity for individual patient as well as reducing public health expenditure.

Citation Format: PehYean Cheah, Lai Fun Thean, Michelle Wong, Michelle Lo, Emile Tan, Choong Leong Tang. Identifying germline variants for metastatic risk assessment in sporadic colorectal carcinomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2829.

Enhancer-derived long non-coding RNAs CCAT1 and CCAT2 at rs6983267 has limited predictability for early stage colorectal carcinoma metastasis

Up-regulation of long non-coding RNAs (lncRNAs), colon-cancer associated transcript (CCAT) 1 and 2, was associated with worse prognosis in colorectal cancer (CRC). Nevertheless, their role in predicting metastasis in early-stage CRC is unclear. We measured the expression of CCAT1, CCAT2 and their oncotarget, c-Myc, in 150 matched mucosa-tumour samples of early-stage microsatellite-stable Chinese CRC patients with definitive metastasis status by multiplex real-time RT-PCR assay. Expression of CCAT1, CCAT2 and c-Myc were significantly up-regulated in the tumours compared to matched mucosa (p < 0.0001). The expression of c-Myc in the tumours was significantly correlated to time to metastasis [hazard ratio = 1.47 (1.10–1.97)] and the risk genotype (GG) of rs6983267, located within CCAT2. Expression of c-Myc and CCAT2 in the tumour were also significantly up-regulated in metastasis-positive compared to metastasis-negative patients (p = 0.009 and p = 0.04 respectively). Nevertheless, integrating the expression of CCAT1 and CCAT2 by the Random Forest classifier did not improve the predictive values of ColoMet19, the mRNA-based predictor for metastasis previously developed on the same series of tumours. The role of these two lncRNAs is probably mitigated via their oncotarget, c-Myc, which was not ranked high enough previously to be included in ColoMet19.

Stenting as a bridge to surgery for obstructed stage IV colorectal cancers - long-term outcomes of a 10-year study

INTRODUCTION

Successful stenting of an obstructing colorectal tumor can avert upfront emergency surgery in malnourished obstructed patients with metastatic disease and poor physiological condition. This study aims to evaluate the outcomes of stenting followed by primary colorectal tumor resection among patients with obstructed stage IV colorectal cancer at presentation, over a 10-year period.

METHODS

From 2007 to 2016, a cohort comprising 25 consecutive patients were retrospectively reviewed from a prospectively collected database. The durability of palliation of bowel obstruction, oncological outcomes and factors influencing overall survival were analyzed.

RESULTS

No re-interventions were required for bowel obstruction during the study period. The overall perioperative morbidity rate was 16%, with no postoperative 90-day mortality. Laparoscopic resection rate was 52% and stoma formation rate was 8%. The median overall survival was 24 months for the entire cohort, and the 1-, 3- and 5-year survival rates were 80%, 35% and 23.33% respectively. More than one site of distant metastases, peritoneal involvement, and elevated carcinoembryonic antigen levels were significantly associated with poorer survival outcomes. Patients with peritoneal-only metastasis had worse outcomes, with a median survival of 7 months and no patients surviving beyond 18 months.

CONCLUSION

Stenting followed by resection of the primary obstructing colorectal cancer provides durable palliation among patients with stage IV disease, with low perioperative morbidity and stoma formation rates. Superior survival was observed among patients with single-site, non-peritoneal distant metastases.

Prediction of overall survival following colorectal cancer surgery in elderly patients

BACKGROUND

With advanced age and chronic illness, the life expectancy of a patient with colorectal cancer (CRC) becomes less dependent on the malignant disease and more on their pre-morbid condition. Justifying major surgery for these elderly patients can be challenging. An accurate tool demonstrating post-operative survival probability would be useful for surgeons and their patients.

AIM

To integrate clinically significant prognostic factors relevant to elective colorectal surgery in the elderly into a validated pre-operative scoring system.

METHODS

In this retrospective cohort study, patients aged 70 and above who underwent surgery for CRC at Singapore General Hospital between 1 January 2005 and 31 December 2012 were identified from a prospectively maintained database. Patients with evidence of metastatic disease, and those who underwent emergency surgery or had surgery for benign colorectal conditions were excluded from the analysis. The primary outcome was overall 3-year overall survival (OS) following surgery. A multivariate model predicting survival was derived and validated against an equivalent external surgical cohort from Kyungpook National University Chilgok Hospital, South Korea. Statistical analyses were performed using Stata/MP Version 15.1.

RESULTS

A total of 1267 patients were identified for analysis. The median post-operative length of stay was 8 [interquartile range (IQR) 6-12] d and median follow-up duration was 47 (IQR 19-75) mo. Median OS was 78 (IQR 65-85) mo. Following multivariate analysis, the factors significant for predicting overall mortality were serum albumin < 35 g/dL, serum carcinoembryonic antigen ≥ 20 µg/L, T stage 3 or 4, moderate tumor cell differentiation or worse, mucinous histology, rectal tumors, and pre-existing chronic obstructive lung disease. Advanced age alone was not found to be significant. The Korean cohort consisted of 910 patients. The Singapore cohort exhibited a poorer OS, likely due to a higher proportion of advanced cancers. Despite the clinicopathologic differences, there was successful validation of the model following recalibration. An interactive online calculator was designed to facilitate post-operative survival prediction, available at http://bit.ly/sgh_crc. The main limitation of the study was selection bias, as patients who had undergone surgery would have tended to be physiologically fitter.

CONCLUSION

This novel scoring system generates an individualized survival probability following colorectal resection and can assist in the decision-making process. Validation with an external population strengthens the generalizability of this model.

Evaluation of Long-Term Outcomes of Microsatellite Instability Status in an Asian Cohort of Sporadic Colorectal Cancers

PURPOSE

Microsatellite instability in colorectal cancer (CRC) and its long-term outcomes remains poorly studied in Asians. We investigate the prognostic significance of microsatellite instability in an Asian population and assess its clinical impact in patients who undergo adjuvant chemotherapy.

METHODS

Six hundred fifty-four consecutive CRC patients who underwent surgical resection between January 2010 and December 2012 were recruited. Survival was estimated using the Kaplan-Meier approach. Univariate Cox proportional hazard models were used to estimate the hazard ratios for variables associated with survival. A subgroup analyses was performed for stage III patients who underwent chemotherapy to evaluate the prognostic significance of microsatellite instability in this group.

RESULTS

Five hundred ninety-one (90.4%) patients were microsatellite stable (MSS) while 63 (9.6%) were microsatellite instable (MSI). Three years recurrence-free survival (RFS) and disease-specific survival (DSS) were 83.7 versus 73.7% (p = 0.295) and 87.1 versus 91.2% (p = 0.307) in MSS and MSI tumors, respectively. Among stage III patients who received adjuvant therapy, MSI status was found to be an adverse prognostic factor for RFS (HR 2.74 (95% CI 1.43-5.26), p = 0.002). This remained significant on multivariate analysis (HR 2.38 (95% CI 1.15-4.93), p = 0.018). Adjuvant chemotherapy was associated with survival benefit for patients with MSS tumors (HR 0.35, 95% CI 0.17-0.69, p = 0.002) but not MSI tumors (HR 0.67, 95% CI 0.08-8.15, p = 0.750).

CONCLUSIONS

MSI status is not a prognostic indicator in the general CRC population but appears to be an adverse prognostic indicator for RFS in stage III CRC patients who received adjuvant chemotherapy.

Totally-laparoscopic versus laparoscopic-assisted low anterior resection for rectal cancer: are outcomes different?

BACKGROUND

Laparoscopic low anterior resection for rectal cancer has superior short-term benefits compared to open surgery. When operative conditions do not favour a totally-laparoscopic (TL) approach, a hybrid operation can be performed. In this laparoscopic-assisted (LA) approach, mobilization and vessel ligation are performed laparoscopically, with total mesorectal excision and distal transection performed either partially or totally in an extra-corporeal fashion. We compared short-term post-operative and oncological outcomes of both approaches.

METHODS

A prospectively collected database of patients who underwent laparoscopic low anterior resection for rectal cancer between January 2009 and December 2014 was retrospectively analysed. Demographics, post-operative and oncological outcomes were compared.

RESULTS

Of 174 patients, 97 were completed by TL, 62 by LA and the remaining 15 were converted to open. Baseline demographics were similar. LA group compared to TL group had bulkier rectal cancers (6.75 cm³ versus 4.50 cm³ , P = 0.04) which were lower (6 cm versus 7 cm from anal verge, P = 0.02). They were of a more advanced tumour grade and had greater incidence of lymphovascular invasion. Yet, post-operative outcomes such as time to diet, pain scores, hospitalization duration, wound-related and anastomotic complications, 30-day morbidity and mortality were similar. There was no difference in oncological adequacy, including circumferential resection margins, distal margins, lymph node harvest and 2-year local recurrence rates.

CONCLUSION

Laparoscopic-assisted low anterior resection enables minimally invasive rectal surgery to be performed despite unfavourable tumour factors and technical challenges; and compares favourably with TL approach in terms of short-term outcomes and oncological safety.

Abstract 5725: Systematic identification of tumour-specific neoantigens(by whole-genome sequencing) and correlation between tumour neoantigen burden, PD-L1 expression and immune infiltrates in 158Asian colorectal cancers

Background: Somatic mutations are attractive therapeutic targets for “individualized neoantigen vaccines” because of lack of host central tolerance and reduced risk of autoimmunity. Here, we perform large-scale-omic analyses to assess the neoantigen landscape of colorectal cancer (CRC), a cancer largely refractory to immune-checkpoint inhibition.

Methods: We performed whole genome sequencing (WGS) (60x tumor, 30x normal) and deep whole transcriptomic sequencing (RNA-Seq) (∼200x106 reads per tumor) on 158 colorectal cancers of which 32 are microsatellite instability high (MSI-H) tumours and 126 are microsatellite stable (MSS). Whole exome sequencing (200x tumor, 100x normal) was also performed on 120 tumours. HLA typing, somatic mutations, gene expression and neoepitope predictions were computationally evaluated. Inferred HLA-A alleles were orthogonally validated with Pacbio long-read sequencing. Tissue microarrays (TMAs) with tumour core, tumour edge and normal adjacent tissue of these 158 CRCs were constructed. Histopathological analyses using multiplex immunohistochemistry (mIHC) to simultaneously evaluate 7 markers, i.e. cytokeratin (CK), CD3, CD8, FOXP3, CD68, PD-L1, DAPI, have been performed.

Results: The most common HLAs were, by allele count: A*11:01: 56; A*33:03: 38; B*58:01: 33; B*46:01: 29; B*40:01: 26; C*01:02: 41; C*07:02: 33. Inferred HLA-A alleles from WGS data was largely concordant (&gt;90%) with Pacbio long-read sequencing. There were a median of 2,850 (1229-6909) [MSI] & 213 (27-13,835) [MSS] coding variants, from which 10,487 (4,307-27,365) [MSI] & 726.5 (50-59,096) [MSS] possible neoepitopes were derived, after accounting for epitope processing, the normal proteome and general population variome based on dbSNP, Of these, 5,707 (2,608-15,218) [MSI] & 320 (14-25,243) [MSS] neoepitopes are expressed (based on RNA-Seq). Epitope prediction algorithms revealed a median of 423 (17-1,056) [MSI] & 26 (0-1,102) [MSS] bound & expressed neoepitopes. 5 MSS tumors did not have any predicted bound nor expressed neoepitopes, 112 of 126 (89%) of MSS tumors had at least 5 predicted bound, expressed neoepitopes. Histopathological correlations between extent of immune infiltrates in fixed tissues, tumour PD-L1 expression and neoantigen burden is ongoing.

Conclusions: There is substantial variability in the neoantigen landscape amongst MSI & MSS CRCs. MSI contains multiple-fold higher neo-antigens. Amongst MSS tumours, 89% of patients have at least 5 predicted bound and expressed neo-epitopes that could be targeted in neoantigen-based vaccines for personalized immunotherapy.

Citation Format: Si-Lin Koo, Joe Poh Sheng Yeong, Andy Nguyen, Clarinda Wei Ling Chua, J Zachary Sanborn, Steve Benz, Wah Siew Tan, Choong Leong Tang, Su Yan, Min Hoe Chew, Brian Goh, Chung Yip Chan, Xiao Qing Koh, Alexander Lezhava, Tony Kiat Hon Lim, Shahrooz Rabizadeh, Anders Skanderup, Iain Beehuat Tan. Systematic identification of tumour-specific neoantigens(by whole-genome sequencing) and correlation between tumour neoantigen burden, PD-L1 expression and immune infiltrates in 158Asian colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5725.

Abstract 1147: Developing an individualized human colonic crypt cell culture as an ex vivo model for immunotherapy

Colorectal Cancer (CRC) is the third leading cause of cancer death worldwide. Majority of mortality is attributable to metastasis to distal organs. Current treatment targeting the ERK/MAPK pathway used monoclonal anti-EGFR antibody after the first line of chemotherapy fails. However these treatments are only effective for a small percentage of patients with wild-type KRAS, and these same patients eventually develop resistance. Small molecule drugs are toxic and have limited success. A combination of antibodies is an attractive alternative. This study aims to investigate whether anti-KRAS antibody can enter live cells in an individualized ex vivo culture system and whether it can bind and inactivate KRAS. The transient culture has advantages over cell line study as it better mimics the human colonic environment and tumors can be compared to their matched normals to partially address the problem of heterogeneity. Samples were obtained from patients' resected tumour and matched mucosa, cultured ex vivo, and immunostaining performed. We show that anti-KRAS antibody is internalized in both the cultured mucosa and tumor crypt cells prior to fixation. Subcellular localization of the internalized antibody in the mucosa cells is similar in the pre-fixed and post-fixed cells. In contrast, the internal cell membrane staining observed in post-fixed tumor cells appear more cytoplasmic and 'punctated' in the pre-fixed tumors, mimicking that of the mucosa cells suggesting that the internalized anti-KRAS may have altered the sub-cellular localization and hence cycling of KRAS. Furthermore, staining with anti-keratin antibody indicates that live tumor cells treated with anti-KRAS has partial reversal of the phenotype to become more like the regular striated pattern of the matched mucosa. Preliminary double labelling of cultured tumours with monoclonal anti-KRAS prior to fixation and polyclonal anti-KRAS post-fixation revealed punctate staining of KRAS in the cytoplasm that were mainly non-overlapping suggesting that the punctate structures are in different compartments.

Citation Format: Peh Yean Cheah, Yee Syuen Low, Michelle Lo, See Aik Tang, Alphaeus Ng, Choong Leong Tang, Siew Heng Wong. Developing an individualized human colonic crypt cell culture as an ex vivo model for immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1147.

Human colorectal cancer initiation is bidirectional, and cell growth, metabolic genes and transporter genes are early drivers of tumorigenesis

The role of stem cells in the development of solid tumors remains controversial. In colorectal cancers (CRC), this is complicated by the conflicting "top-down" or "bottom-up" hypotheses of cancer initiation. We profiled the expressions of genes from the top (T) and bottom (B) crypt fractions of normal-appearing human colonic mucosa (M) at least 20 cm away from the tumor as a baseline and compared this to the genes of matched mucosa adjacent to tumors (M_T) in twenty-three sporadic CRC patients. In thirteen patients, the genetic distance (M-M_T) between the B fractions is smaller than the distance between the T fractions, indicating that the expressions diverge further in the top fractions (B < T). In the remaining patients, the reverse effect is observed (B > T). Assuming that a greater genetic divergence in the top or bottom fractions indicates that position as the initiation site, it is thus equally likely that human CRC initiates from 'top-down' via de-differentiated colonocytes or 'bottom-up' via dysregulated intestinal stem cells. Dysregulated genes that persist until tumor stage are not limited to tumor suppressors or oncogenes but include metabolic and transporter genes such as CA7, PHLPP2, and AQP8.

A Case of Emphysematous Cystitis

Emphysematous cystitis (EC) is an uncommon but potentially life-threatening urinary tract infection. Diagnostic difficulty exists because of the variable presentations. We report the case of a 73-year-old woman who presented with diarrhoea and malaise, and emphysematous cystitis was revealed on the abdominal X-ray. As she was treated for EC, the diarrhoea and the radiographic abnormalities of EC also resolved. The evaluation and management of this complicated urinary tract infection are discussed.

Genome-wide association study identified copy number variants associated with sporadic colorectal cancer risk

Background

Multiple single nucleotide polymorphisms (SNPs) have been associated with colorectal cancer (CRC) risk. The role of structural or copy number variants (CNV) in CRC, however, remained unclear. We investigated the role of CNVs in patients with sporadic CRC.

Methods

A genome-wide association study (GWAS) was performed on 1000 Singapore Chinese patients aged 50 years or more with no family history of CRC and 1000 ethnicity-matched, age-matched and gender-matched healthy controls using the Affymetrix SNP 6 platform. After 16 principal component corrections, univariate and multivariate segmentations followed by association testing were performed on 1830 samples that passed quality assurance tests.

Results

A rare CNV region (CNVR) at chromosome 14q11 (OR=1.92 (95% CI 1.59 to 2.32), p=2.7e-12) encompassing CHD8, and common CNVR at chromosomes 3q13.12 (OR=1.54 (95% CI 1.33 to 1.77), p=2.9e-9) and 12p12.3 (OR=1.69 (95% CI 1.41 to 2.01), p=2.8e-9) encompassing CD47 and RERG/ARHGDIB, respectively, were significantly associated with CRC risk. CNV loci were validated in an independent replication panel using an optimised copy number assay. Whole-genome expression data in matched tumours of a subset of cases demonstrated that copy number loss at CHD8 was significantly associated with dysregulation of several genes that perturb the Wnt, TP53 and inflammatory pathways.

Conclusions

A rare CNVR at 14q11 encompassing the chromatin modifier CHD8 was significantly associated with sporadic CRC risk. Copy number loss at CHD8 altered expressions of genes implicated in colorectal tumourigenesis.

[Effect of nicotinic acetylcholine receptor α7 subunit gene on liver inflammatory reaction in mice with nonalcoholic steatohepatitis and related mechanisms]

Objective: To investigate the effect of nicotinic acetylcholine receptor α7 (α7nAChR) subunit gene on liver inflammation in mice with nonalcoholic steatohepatitis (NASH) and related mechanisms. Methods: C57BL/6J mice and α7nAChR gene knockout mice were fed for 24 weeks to establish the NASH model, and the mice were sacrificed to isolate and culture the primary liver macrophages. After the treatment with nicotine and endotoxin, ELISA was used to measure the levels of the inflammatory factors interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in supernatant; indirect immunofluorescence assay and Western blot were used to observe the effect on the NF-κB signaling pathway, and quantitative PCR was used to measure the mRNA expression of Toll-like receptor-4 (TLR-4) in macrophages. An analysis of variance was used for comparison of means between multiple groups. Results: The results of ELISA showed that compared with the endotoxin+nicotine group of C57 NASH mice, the endotoxin+nicotine group of gene knockout NASH mice had significantly higher levels of IL-6 and TNF-α in supernatant (IL-6: 1 599±65 pg/ml vs 1 465±45 pg/ml, P < 0.05; TNF-α: 1 567±66 pg/ml vs 1 433±50 pg/ml, P < 0.05). The results of Western blot showed that compared with the endotoxin+nicotine group of C57 NASH mice, the endotoxin+nicotine group of gene knockout NASH mice had significantly higher relative protein expression of phosphorylated NF-κB and TLR-4 (NF-κB: 69 425±600 vs 51 133±200, P < 0.05; TLR-4: 93 387±684 vs 64 198±630, P < 0.05). The results of indirect immunofluorescence assay showed that the endotoxin+nicotine group of gene knockout NASH mice had a significantly higher fluorescence intensity of NF-κB than the endotoxin+nicotine group of C57 NASH mice. The results of PCR showed that the endotoxin+nicotine group of gene knockout NASH mice had significantly higher relative mRNA expression of TLR-4 than the endotoxin+nicotine group of C57 NASH mice (4.13±0.13 vs 2.93±0.14, P < 0.05). Conclusion: The α7nAChR gene knockout can aggravate the degree of inflammatory reaction in NASH, and its mechanism may be related to the fact that the NF-κB signaling pathway cannot be inhibited, which aggravates inflammatory reaction.

Critical evaluation of contemporary management in a new Pelvic Exenteration Unit: The first 25 consecutive cases

AIM

To critically appraise short-term outcomes in patients treated in a new Pelvic Exenteration (PE) Unit.

METHODS

This retrospective observational study was conducted by analysing prospectively collected data for the first 25 patients (16 males, 9 females) who underwent PE for advanced pelvic tumours in our PE Unit between January 2012 and October 2016. Data evaluated included age, co-morbidities, American Society of Anesthesiologists (ASA) score, Eastern Cooperative Oncology Group (ECOG) status, preoperative adjuvant treatment, intra-operative blood loss, procedural duration, perioperative adverse event, lengths of intensive care unit (ICU) stay and hospital stay, and oncological outcome. Quantitative data were summarized as percentage or median and range, and statistically assessed by the χ² test or Fisher’s exact test, as applicable.

RESULTS

All 25 patients received comprehensive preoperative assessment via our dedicated multidisciplinary team approach. Long-course neoadjuvant chemoradiotherapy was provided, if indicated. The median age of the patients was 61.9-year-old. The median ASA and ECOG scores were 2 and 0, respectively. The indications for PE were locally invasive rectal adenocarcinoma (n = 13), advanced colonic adenocarcinoma (n = 5), recurrent cervical carcinoma (n = 3) and malignant sacral chordoma (n = 3). The procedures comprised 10 total PEs, 4 anterior PEs, 7 posterior PEs and 4 isolated lateral PEs. The median follow-up period was 17.6 mo. The median operative time was 11.5 h. The median volume of blood loss was 3306 mL, and the median volume of red cell transfusion was 1475 mL. The median lengths of ICU stay and of hospital stay were 1 d and 21 d, respectively. There was no case of mortality related to surgery. There were a total of 20 surgical morbidities, which occurred in 12 patients. The majority of the complications were grade 2 Clavien-Dindo. Only 2 patients experienced grade 3 Clavien-Dindo complications, and both required procedural interventions. One patient experienced grade 4a Clavien-Dindo complication, requiring temporary renal dialysis without long-term disability. The R0 resection rate was 64%. There were 7 post-exenteration recurrences during the follow-up period. No statistically significant relationship was found among histological origin of tumour, microscopic resection margin status and postoperative recurrence (P = 0.67). Four patients died from sequelae of recurrent disease during follow-up.

CONCLUSION

By utilizing modern assessment and surgical techniques, our PE Unit can manage complex pelvic cancers with acceptable morbidities, zero-rate mortality and equivalent oncologic outcomes.

Chromosome 19q13 disruption alters expressions of CYP2A7, MIA and MIA-RAB4B lncRNA and contributes to FAP-like phenotype in APC mutation-negative familial colorectal cancer patients

Familial adenomatous polyposis (FAP) is an autosomal-dominantly inherited form of colorectal cancer (CRC) caused by mutation in the adenomatous polyposis coli (APC) gene. Our ability to exhaustively screen for APC mutations identify microsatellite-stable and APC-mutation negative familial CRC patients, enabling us to search for novel genes. We performed genome-wide scan on two affected siblings of one family and 88 ethnicity- and gender-matched healthy controls to identify deletions shared by the siblings. Combined loss of heterozygosity, copy number and allelic-specific copy number analysis uncovered 5 shared deletions. Long-range polymerase chain reaction (PCR) confirmed chromosome 19q13 deletion, which was subsequently found in one other family. The 32 kb deleted region harbors the CYP2A7 gene and was enriched with enhancer, repressor and insulator sites. The wildtype allele was lost in the polyps of the proband. Further, real-time RT-PCR assays showed that expressions of MIA and MIA-RAB4B located 35 kb upstream of the deletion, were up-regulated in the polyps compared to the matched mucosa of the proband. MIA-RAB4B, the read-through long non-coding RNA (lncRNA), RAB4B, PIM2 and TAOK1 share common binding site of a microRNA, miR-24, in their 3'UTRs. PIM2 and TAOK1, two target oncogenes of miR-24, were co-ordinately up-regulated with MIA-RAB4B in the polyps, suggesting that MIA-RAB4B could function as competitive endogenous RNA to titrate miR-24 away from its other targets. The data suggest that the 19.13 deletion disrupted chromatin boundary, leading to altered expression of several genes and lncRNA, could contribute to colorectal cancer via novel genetic and epigenetic mechanisms.

[Features and advances of Morse taper connection in oral implant]

Dental implants have been widely accepted as a predictable and reliable tool for dental reconstruction with the development of the economy. The design of implant-abutment connections has influence on mechanical properties and biological characteristics of implants. There are two types of implant-abutment connections, the external and the internal connections. Morse taper connection is one of the internal connections and its conical shape creates significant friction via the high propensity of parallelism between the two structures within the joint space. Several studies showed that Morse taper connection performed well in terms of survival rate, stability, bacterial seal and marginal bone loss. Recently, clinical studies indicate implants combining Morse taper connection with platform switching are helpful in reducing marginal bone absorption. This review aims at analyzing the features and advantages of Morse taper connection.

Efficient biosynthesis of d-ribose using a novel co-feeding strategy in Bacillus subtilis without acid formation

Normally, low d-ribose production was identified as responsible for plenty of acid formation by Bacillus subtilis due to its carbon overflow. An approach of co-feeding glucose and sodium citrate is developed here and had been proved to be useful in d-ribose production. This strategy is critical because it affects the cell concentration, the productivity of d-ribose and, especially, the formation of by-products such as acetoin, lactate and acetate. d-ribose production was increased by 59·6% from 71·06 to 113·41 g l^-1 without acid formation by co-feeding 2·22 g l^-1  h^-1 glucose and 0·036 g l^-1  h^-1 sodium citrate to a 60 g l^-1 glucose reaction system. Actually, the cell density was also enhanced from 11·51 to 13·84 g l^-1 . These parameters revealed the importance of optimization and modelling of the d-ribose production process. Not only could zero acid formation was achieved over a wide range of co-feeding rate by reducing glycolytic flux drastically but also the cell density and d-ribose yield were elevated by increasing the hexose monophosphate pathway flux.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacillus subtilis usually produce d-ribose accompanied by plenty of organic acids when glucose is used as a carbon source, which is considered to be a consequence of mismatched glycolytic and tricarboxylic acid cycle capacities. This is the first study to provide high-efficiency biosynthesis of d-ribose without organic acid formation in B. subtilis, which would be lower than the cost of separation and purification. The strain transketolase-deficient B. subtilis CGMCC 3720 can be potentially applied to the production of d-ribose in industry.

Factors Affecting the Enhancement Patterns of Intrahepatic Cholangiocarcinoma (ICC) on Contrast-Enhanced Ultrasound (CEUS) and their Pathological Correlations in Patients with a Single Lesion

Purpose: To investigate the factors that influence the enhancement patterns of intrahepatic cholangiocarcinomas (ICC) on contrast-enhanced ultrasound (CEUS) and analyze the correlations between the enhancement patterns on CEUS and pathological findings. Materials and Methods: Ninety-six patients with 96 pathologically confirmed ICCs underwent CEUS. CEUS images were retrospectively evaluated for tumor enhancement patterns in the arterial, portal and late phases. The arterial enhancement patterns were correlated with clinicopathological factors. The possible influencing factors were correlated with pathologic findings. Results: Thirty-six patients with ICC demonstrated rim-like enhancement, and 60 exhibited non-rim-like enhancement in the arterial phase on CEUS. The incidence of non-rim-like-enhancing ICCs was higher in patients with cirrhosis and chronic viral hepatitis than patients with no chronic liver disease (p = 0.001). The sizes of the ICCs with homogeneous hyper-enhancement were significantly smaller than those with inhomogeneous hyper-enhancement (p = 0.007). Arterial non-rim-like-enhancing ICCs showed higher microvessel density (MVD) and arterial density (AD) and less fibrous stroma and necrosis than rim-like-enhancing ICCs. Arterial inhomogeneous-enhancing ICCs had lower MVD and AD and much more fibrous stroma and necrosis than homogeneous-enhancing ICCs. Conclusion: The enhancement pattern of ICCs in the arterial phase on CEUS was affected by a liver cirrhosis and chronic viral hepatitis and tumor size. The amount of MVD, AD, fibrous stroma and necrosis in ICC tumors may be responsible for the difference in the enhancement patterns.

[Nicotine alleviates the liver inflammation of non-alcoholic steatohepatitis induced by high-fat and high-fructose in mice]

OBJECTIVE

To investigate the anti-inflammation effects by activation of the cholinergic anti-inflammatory pathway and its mechanisms in non-alcoholic steatohepatitis (NASH) model mice.

METHODS

6-week-old male C57BL/6J (B6) mice were randomly divided into four groups: the first group was normal mice, injected with saline; the second group was normal mice, injected with nicotine; the third group was NASH model mice, injected with saline; the fourth group was NASH model mice, injected with nicotine. The experimental mice were fed with either standard chow (SC) or high-fat and high-fructose (HFHF) for 17 weeks to generate an NASH model mice. The mice received injection once daily for 3 weeks [nicotine dose, 400 μg/kg]. Then, their pathological characteristics and function of the liver were assessed. The expressions of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in serum were analyzed by enzyme linked immunosorbent assay (ELISA). The expressions of alpha 7 nicotinic acetylcholine receptors (α7nAChR), Toll-like receptors-4 (TLR-4) and nuclear factor κB of phosphory-lation (p-NF-κB) in Kupffer cells were determined by Western blot and immunofluorescence assays.

RESULTS

We successfully generated NASH model mice by imitating the high-fat and high-fructose dietary style of NASH patients. The results of our investigation demonstrated that nicotine could reduce significantly the levels of IL-6, and TNF-α in serum (P<0.05). The expression of p-NF-κB protein in the group which was NASH model mice injected with nicotine declined significantly as compared with the group which was NASH model mice injected with saline (P<0.05). And the expression of α7nAChR protein elevated significantly conversely (P<0.05).

CONCLUSION

Activation of the cholinergic anti-inflammatory pathway could inhibit the release of inflammatory factors as TNF-α and IL-6 in NASH model mice, and the mechanism for the inhibition of inflammatory was mediated by NF-κB pathway.

Methylation of serum SST gene is an independent prognostic marker in colorectal cancer

There is an increasing demand for accurate prognostication for colorectal cancer (CRC). This study sought to assess prognostic potentials of methylation targets in the serum of CRC patients. A total of 165 CRC patients were enrolled in this prospective study. Promoter methylation levels of seven genes in pre-operative sera and matched tumor tissues were evaluated by quantitative methylation-specific PCR. Kaplan-Meier test, and univariate and multivariate Cox proportional hazards regression models were used for survival analyses. After a median follow-up of 56 months, 43 patients (28.7%) experienced tumor recurrence. In univariate survival analyses, serum methylation levels of SST and MAL were significantly predictive of cancer-specific death (P<0.005 for both). The former was also a significant predictor for tumor recurrence (P=0.007). Independent prognostic effects of serum methylation levels of SST were revealed by multivariate Cox regression model (P=0.031 and P=0.003 for cancer death and recurrence, respectively). When focusing on stage II and III patients, prognostication with serum methylated SST remained significant. Methylated SST detected in all serum samples can be traced back to the matched primary tumor tissues. We believe that methylated SST detected in the pre-operative sera of CRC patients appear to be a novel promising prognostic marker and probably can be auxiliary to tumor staging system and serum carcinoembryonic antigen towards better risk stratification.

Abstract 2559: Genome-wide haplotype association tests identified three candidate loci associated with sporadic colorectal cancer risk in Singapore Chinese

Colorectal cancer (CRC) is one of the most frequent cancers and leading cause of cancer mortality in the developed world. Twin study has attributed about 35% of the etiology of sporadic CRC to genes. Hitherto, more than 20 single nucleotide polymorphism (SNP) loci from genome-wide association studies (GWAS) were associated with CRC risk. Most of these index SNPs however have small effect sizes and often located in gene deserts. Thus they are unlikely to be causal. Haplotype-based methods may offer a more powerful approach to disease gene mapping. We previously performed a GWAS on 2,000 ethnicity-, age-, and gender-matched Singapore Chinese CRC patients and healthy controls using the Affymetrix SNP 6 platform. Sporadic patients were defined as aged 50 or more at the time of surgery and with no dominant family history of CRC. Haplotype block detection was performed in Golden Helix SVS after this SNP6 dataset was filtered for genotype call rate (&gt;95%), Hardy-Weinberg equilibrium in the controls and principal component analysis. Block detection was performed requiring strong linkage disequilibrium between block pairs, minor allelic frequencies (MAF) of SNPs more than 0.01, the maximum number of markers and length of the block at 30 and 160kb respectively. Genome-wide, 73,333 blocks were computed using 336, 466 markers on 22 autosomes. Haplotype frequencies were estimated using the EM algorithm. Chi-Squared and logistic regression with odds ratio tests of haplotype association were performed using these pre-computed blocks on a per-haplotype basis. Three candidate loci at chromosomes 3, 15 and 20, each with 6 to 9 SNPs and sizes ranging from 4 to 15 kb achieved genome-wide significance and encompass potential novel disease genes. These loci are currently being validated in an independent replication panel using the Fluidgm SNPtype assays and pooled analyses will be performed.

Citation Format: Peh Yean Cheah, Lai Fun Thean, Yik Ying Teo, Woon-Puay Koh, Jian-Min Yuan, Min Hoe Chew, Choong Leong Tang. Genome-wide haplotype association tests identified three candidate loci associated with sporadic colorectal cancer risk in Singapore Chinese. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2559.

Critical appraisal of laparoscopic vs open rectal cancer surgery

AIM: To evaluate the long-term clinical and oncological outcomes of laparoscopic rectal resection (LRR) and the impact of conversion in patients with rectal cancer.

METHODS: An analysis was performed on a prospective database of 633 consecutive patients with rectal cancer who underwent surgical resection. Patients were compared in three groups: Open surgery (OP), laparoscopic surgery, and converted laparoscopic surgery. Short-term outcomes, long-term outcomes, and survival analysis were compared.

RESULTS: Among 633 patients studied, 200 patients had successful laparoscopic resections with a conversion rate of 11.1% (25 out of 225). Factors predictive of survival on univariate analysis include the laparoscopic approach (P = 0.016), together with factors such as age, ASA status, stage of disease, tumor grade, presence of perineural invasion and vascular emboli, circumferential resection margin < 2 mm, and postoperative adjuvant chemotherapy. The survival benefit of laparoscopic surgery was no longer significant on multivariate analysis (P = 0.148). Neither 5-year overall survival (70.5% vs 61.8%, P = 0.217) nor 5-year cancer free survival (64.3% vs 66.6%, P = 0.854) were significantly different between the laparoscopic group and the converted group.

CONCLUSION: LRR has equivalent long-term oncologic outcomes when compared to OP. Laparoscopic conversion does not confer a worse prognosis.

Palliative surgical intervention in metastatic colorectal carcinoma: a prospective analysis of quality of life

AIM

Quality of life (QOL) was assessed after palliative surgery for incurable metastatic colorectal cancer (CRC).

METHOD

Newly diagnosed patients with incurable metastatic CRC who were offered elective palliative surgical intervention were included. The European Organization for Research and Treatment of Cancer QLQ-C30 and QLQ-CR29 questionnaire was used for the assessment of QOL at baseline and at 3 and 6 months after surgery. Generalized estimating equations were used to estimate the mean change in the QOL score from baseline.

RESULTS

Twenty-four patients formed the study group. Sixteen underwent resection of the primary tumour and eight had a proximal diversion or bypass. The Global Health (GH) score and Social Functioning (SF) score improved at 3 and 6 months after intervention respectively (GH +11, P = 0.021; SF +15, P = 0.005). Mean anxiety scores were markedly improved from the baseline of 51 to 71 (P = 0.004, 3 months) and 76 (P = 0.002, 6 months). Weight concerns also improved significantly when compared with baseline (3 months, +20, P < 0.001; 6 months, +14, P = 0.012). Symptoms of diarrhoea (3 months, --17, P = 0.007; 6 months,--16, P = 0.008) and nausea (--8, P = 0.032) improved.

CONCLUSION

In patients with incurable metastatic CRC, surgery improved QOL.

A scoring model for predicting survival following primary tumour resection in stage IV colorectal cancer patients with unresectable metastasis

BACKGROUND

Stage IV colorectal cancer patients with unresectable metastasis who undergo elective primary tumour resection experience heterogeneous post-operative survival. We aimed to develop a scoring model for predicting post-operative survival using pre-operative variables to identify patients who are least likely to experience extended survival following the procedure.

METHODS

Survival data were collected from stage IV colorectal cancer patients who had undergone elective primary tumour resection between January 1999 and December 2007. Coefficients of significant covariates from the multivariate Cox regression model were used to compute individual survival scores to classify patients into three prognostic groups. A survival function was derived for each group via Kaplan-Meier estimation. Internal validation was performed.

RESULTS

Advanced age (hazard ratio, HR 1.43 (1.16-1.78)); poorly differentiated tumour (HR 2.72 (1.49-5.04)); metastasis to liver (HR 1.76 (1.33-2.33)), lung (HR 1.37 (1.10-1.71)) and bone (HR 2.08 ((1.16-3.71)); carcinomatosis (HR 1.68 (1.30-2.16)); hypoalbuminaemia (HR 1.30 (1.04-1.61) and elevated carcinoembryonic antigen levels (HR 1.89 (1.49-2.39)) significantly shorten post-operative survival. The scoring model separated patients into three prognostic groups with distinct median survival lengths of 4.8, 12.4 and 18.6 months (p < 0.0001). Internal validation revealed a concordance probability estimate of 0.65 and a time-dependent area under receiver operating curve of 0.75 at 6 months. Temporal split-sample validation implied good local generalizability to future patient populations (p < 0.0001).

CONCLUSION

Predicting survival following elective primary tumour resection using pre-operative variables has been demonstrated with the scoring model developed. Model-based survival prognostication can support clinical decisions on elective primary tumour resection eligibility.

Analysis of colorectal cancer glyco-secretome identifies laminin β-1 (LAMB1) as a potential serological biomarker for colorectal cancer

The high mortality rate in colorectal cancer is mostly ascribed to metastasis, but the only clinical biomarker available for disease monitoring and prognosis is the carcinoembryonic antigen (CEA). However, the prognostic utility of CEA remains controversial. In an effort to identify novel biomarkers that could be potentially translated for clinical use, we collected the secretomes from the colon adenocarcinoma cell line HCT-116 and its metastatic derivative, E1, using the hollow fiber culture system, and utilized the multilectin affinity chromatography approach to enrich for the secreted glycoproteins (glyco-secretome). The HCT-116 and E1 glyco-secretomes were compared using the label-free quantitative SWATH-MS technology, and a total of 149 glycoproteins were differentially secreted in E1 cells. Among these glycoproteins, laminin β-1 (LAMB1), a glycoprotein not previously known to be secreted in colorectal cancer cells, was observed to be oversecreted in E1 cells. In addition, we showed that LAMB1 levels were significantly higher in colorectal cancer patient serum samples as compared to healthy controls when measured using ELISA. ROC analyses indicated that LAMB1 performed better than CEA at discriminating between colorectal cancer patients from controls. Moreover, the diagnostic performance was further improved when LAMB1 was used in combination with CEA.

Abstract 4587: Genome-wide copy number analysis identified a copy number polymorphism at chromosome 8p11 associated with sporadic colorectal cancer risk in Singapore Chinese

Colorectal cancer (CRC) is one of the most frequent cancers and leading cause of cancer mortality in the developed world. Twin study has attributed about 35% of the etiology of sporadic CRC to genes. Hitherto, more than 20 single nucleotide polymorphism (SNP) loci have been associated with CRC risk. The role of structural variant in CRC, however, remains unclear. We performed genome-wide association study (GWAS) on 2,000 ethnicity-, age-, and gender-matched Singapore Chinese CRC patients (aged 50 or more and with no dominant family history of CRC) and healthy controls. Genome-wide genotyping was performed using Affymetrix SNP 6 platform. Copy number polymorphism (CNP) was interrogated in 1830 samples that passed quality assurance tests using a multivariate segmentation algorithm. A 150 kb region at chromosome 8p11 was identified to be significantly associated (-log10 p-value = 29) with sporadic CRC risk. This CNP was preferentially amplified in the cases compared to the controls. The amplification was not gender-specific suggesting that it is not involved in gender-limiting pathway. It is now being replicated in an independent panel using digital polymerase chain reaction (dPCR) and multiplex endogenous reference technique. In silico analysis of a 1.5 Mb region encompassing the CNP reveals a candidate gene 300kb 5′ of the CNP previously implicated in cancer progression. The expression of this gene in cases with copy number and metastasis status is being interrogated.

Citation Format: Peh Yean Cheah, Lai Fun Thean, Yik Ying Teo, Woon-Puay Koh, Jian-Min Yuan, Min Hoe Chew, Choong Leong Tang. Genome-wide copy number analysis identified a copy number polymorphism at chromosome 8p11 associated with sporadic colorectal cancer risk in Singapore Chinese. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4587. doi:10.1158/1538-7445.AM2015-4587

Genomics of Hereditary Colorectal Cancer: Lessons Learnt from 25 Years of the Singapore Polyposis Registry

INTRODUCTION

The Singapore Polyposis Registry (SPR) was established in 1989 in Singapore General Hospital (SGH). The aims were to provide a central registry service to facilitate identification, surveillance and management of families and individuals at high risk of colorectal cancer.

MATERIALS AND METHODS

This is a review of published literature in the department.

RESULTS

The registry currently has 253 families with several genetic conditions-93 familial adenomatous polyposis (FAP) families, 138 Amsterdam-criteria positive presumed Lynch syndrome (LS) families, 12 families with Peutz Jeghers syndrome, 2 families with Cowden's syndrome, and 8 families with hereditary mixed polyposis syndrome (HMPS). There are also 169 families with a strong family history of colorectal cancer but no abnormal genes yet identified. In FAP, a diagnostic tool developed has allowed a 94% local APC germline detection rate in FAP families. Knowledge obtained studying the phenotype of FAP patients has allowed better choice of surgery between ileal pouch anal anastomosis (IPAA) against an ileal-rectal anastomosis (IRA). In LS, our review has noted a highly heterogenous mutational spectrum and novel variants made up 46.7% (28/60) of all variants identified in this cohort. This may suggest that our Southeast Asian ethnic groups have distinct mutational variants from Western populations. Pathogenic mutations were only confined to MLH1 and MSH2, and identified in 28.8% of families.

CONCLUSION

The impact of predictive gene testing for hereditary cancer risk in clinical practice has allowed evolution of care. Risk-reducing surgery and aggressive surveillance allows reduction in morbidity and mortality of patients. The SPR will continue to grow and improve outcomes in hereditary colorectal cancer patients and families.

Post-operative aspirin use and colorectal cancer-specific survival in patients with stage I-III colorectal cancer

BACKGROUND

Recent observational studies suggest that postoperative aspirin use may improve Colorectal cancer (CRC)-specific survival and overall survival (OS). In this study, we aimed to assess the effects of aspirin use on outcomes in a predominantly Asian cohort of patients with CRC.

PATIENTS AND METHODS

Case records of patients undergoing curative resection for stage I-III CRC were retrieved for clinical data and patterns of aspirin use and vital data were determined from hospital electronic prescription records, hospital pharmacy dispensing records, national clinical and prescription databases. CRC-specific and recurrence-free survival (RFS) amongst aspirin users and non-users were analyzed and compared using the Cox proportional hazards model.

RESULTS

Out of 726 patients with CRC, 103 were regular aspirin users and 623 were non-users. The median age of the cohort was 65 years (range=22-94 years) and the majority of patients were Chinese (90%). Nineteen percent, 31% and 47% had stage I, II and III CRC respectively; tumor staging was unknown for 3%. After adjusting for prognostic factors (age, stage, lymph node stage, grade, lesion site, perineural invasion, lymphvascular invasion), the risk of CRC relapse or death from CRC was approximately 60% lower compared to patients who were not postoperative aspirin users (Hazard Ratio=0.38, 95% Confidence Interval=0.17-0.84, p=0.017). No benefit was observed for preoperative use of aspirin.

CONCLUSION

In this single-Institution study, with long-term follow-up of patients with stage I-III-resected CRC, postoperative aspirin use was associated with reduced risk of relapse of and death from CRC.

Jejunojejunal intussusception secondary to submucosal lipoma resulting in a 5-year history of intermittent abdominal pain

Jejunal lipomata are an unusual cause of adult intussusception. We report a case of a 44-year-old Chinese woman who presented with a 3-day history of abdominal pain and nausea; she had a 5-year history of similar episodic symptoms after meals. Contrast-enhanced CT revealed a fat-density lead point in the jejunum resulting in intussusception. Single port laparoscopic surgery was performed with reduction of the intussusception, bowel resection and primary anastamosis. Histology confirmed a benign submucosal lipoma. We discuss the recent published literature on this rare entity and show CT images and intraoperative pictures.

Abstract 2189: A rare copy number variant at chromosome 14q11 was associated with sporadic colorectal cancer risk in Singapore Chinese

Colorectal cancer (CRC) is one of the most frequent cancers and leading cause of cancer mortality in the developed world. Twin study has attributed about 35% of the etiology of sporadic CRC to genes. Structural variations in the human genome have recently been associated with complex neurological diseases. Their role in CRC, however, is unclear. We performed genome-wide association study (GWAS) on 2,000 ethnicity-, age-, and gender-matched Singapore Chinese CRC patients (aged 50 or more and with no dominant family history of CRC) and healthy controls. Genome-wide genotyping was performed using Affymetrix SNP 6 platform, and rare copy number variants (CNV) were interrogated in 1830 samples that passed the quality assurance tests. A 400 kb region at chromosome 14q11 was identified to be significantly associated (-log10 p-value = 11) with sporadic CRC risk. A chromatin modifier implicated in the β-catenin/Wnt signalling pathway is one of the candidate genes found in the region. Primers unique for this gene applied to an optimal real-time copy number assay verified the CNV region in an independent replication panel comprising another 1,000 sporadic CRC cases. About 6% of the cases exhibit copy number alterations at this region compared to 1% in the healthy controls. A second gene, a small guanosine triphosphatase (GTPase) involved in protein trafficking and preferentially up-regulated in colonic tumors , was shown by long-range polymerase chain reaction to have more structural variations in the cases compared to the controls. Furthermore, expression of the H1 binding domain of the chromatin modifier was positively correlated to the expressions of Cyclin D1 and C-myc. The data suggest that the rare CNV in 14q11 was dynamically associated with the activation of genes implicated in sporadic CRC in the Singapore Chinese.

Citation Format: Peh Yean Cheah, Lai Fun Thean, Yik-Ying Teo, Woon-Puay Koh, Jian-Min Yuan, Poh Koon Koh, Min Hoe Chew, Choong Leong Tang. A rare copy number variant at chromosome 14q11 was associated with sporadic colorectal cancer risk in Singapore Chinese. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2189. doi:10.1158/1538-7445.AM2014-2189

Tracheotomy: an alternative for tracheobronchial foreign body removal

A 6 years old girl accidentally aspirated a plastic whistle while playing. Computed Tomography of thorax showed foreign body at carina level. Rigid bronchoscope under general anesthesia was attempted but unable to extract the whistle through vocal cord. Tracheostomy was later performed and foreign body was removed.

Evolution of laparoscopy in colorectal surgery: An evidence-based review

Open surgery for colorectal disease has progressed significantly over the past century from humble beginnings to form the mainstay of treatment for colorectal cancer and a number of benign conditions. Following the introduction of laparoscopic abdominal surgery, the next stage in the evolution of the specialty began in the 1990s with the first laparoscopic colonic resection. Following some early concerns regarding its safety and oncological efficacy during the latter part of that decade, laparoscopic colorectal surgery rapidly came into mainstream use in the early part of the current century with evidence supporting its use being made available from large scale randomised controlled trials. This article provides an evidence-based summary of this evolutionary process as it relates to both benign and malignant colorectal disease, as well as discussion of the next phase of new technologies such as robotic surgery.

Systematic study on genetic and epimutational profile of a cohort of Amsterdam criteria-defined Lynch Syndrome in Singapore

Background

Germline defects of mismatch repair (MMR) genes underlie Lynch Syndrome (LS). We aimed to gain comprehensive genetic and epigenetic profiles of LS families in Singapore, which will facilitate efficient molecular diagnosis of LS in Singapore and the region.

Methods

Fifty nine unrelated families were studied. Mutations in exons, splice-site junctions and promoters of five MMR genes were scanned by high resolution melting assay followed by DNA sequencing, large fragment deletions/duplications and promoter methylation in MLH1, MSH2, MSH6 and PMS2 were evaluated by multiplex ligation-dependent probe amplification. Tumor microsatellite instability (MSI) was assessed with five mononucleotide markers and immunohistochemical staining (IHC) was also performed.

Results

Pathogenic defects, all confined to MLH1 and MSH2, were identified in 17 out of 59 (28.8%) families. The mutational spectrum was highly heterogeneous and 28 novel variants were identified. One recurrent mutation in MLH1 (c.793C>T) was also observed. 92.9% sensitivity for indication of germline mutations conferred by IHC surpassed 64.3% sensitivity by MSI. Furthermore, 15.6% patients with MSS tumors harbored pathogenic mutations.

Conclusions

Among major ethnic groups in Singapore, all pathogenic germline defects were confined to MLH1 and MSH2. Caution should be applied when the Amsterdam criteria and consensus microsatellite marker panel recommended in the revised Bethesda guidelines are applied to the local context. We recommend a screening strategy for the local LS by starting with tumor IHC and the hotspot mutation testing at MLH1 c.793C>T followed by comprehensive mutation scanning in MLH1 and MSH2 prior to proceeding to other MMR genes.

Serum methylation levels of TAC1. SEPT9 and EYA4 as diagnostic markers for early colorectal cancers: a pilot study

OBJECTIVE

To identify methylated genes in serum with diagnostic potentials for early colorectal cancer (CRC).

METHODS

Serum methylation levels of up to 12 genes were measured in two sets of serum samples with the second set from 26 stage I CRC patients and 26 age/gender-matched controls.

RESULTS

Serum methylation levels of TAC1, SEPT9, and EYA4 were significant discriminants between stage I CRC and healthy controls. Combination of TAC1 and SEPT9 rendered 73.1% sensitivity with 92.3% specificity.

CONCLUSION

Serum methylation levels of TAC1. SEPT9 and EYA4 may be useful biomarkers for early detection of CRC though a validation study is necessary.

Opportunistic screening for colorectal neoplasia in Singapore using faecal immunochemical occult blood test

INTRODUCTION

The use of faecal immunochemical occult blood test (FIT) has been reported to decrease mortality from colorectal cancer. The Singapore Cancer Society (SCS) gives out FIT kits to encourage opportunistic screening of colorectal cancer. Any Singapore citizen or permanent resident aged ≥ 50 years is eligible to receive two FIT kits. Participants with at least one positive FIT are referred for further evaluation. We aimed to analyse the results of SCS data from the year 2008.

METHODS

The factors evaluated included compliance, positive test rate (PR) and positive predictive value (PPV) of FIT.

RESULTS

20,989 participants received 41,978 kits in 2008. Compliance was 38.9%, with 8,156 participants returning at least one kit. 8% of participants tested positive, and 75% of these test-positive participants agreed to undergo further investigations. 33 participants had colorectal cancers, 45 had advanced polyps (≥ 1 cm) and 90 had polyps < 1 cm. Histologically, 114 polyps were adenomatous, 20 were hyperplastic and 1 was serrated. PPV of colorectal neoplasia for those who underwent further colonoscopy was 34%. Over half of the participants who had only one positive test had colorectal neoplasia.

CONCLUSION

PR and PPV of FIT in our study were comparable to that in the literature. However, compliance was low and a quarter of all participants who tested positive refused further investigations. Extensive population education programmes are required to improve compliance and tackle inhibitions among the masses. It is also important to take steps to enhance the cost effectiveness of future screening programmes.