MSH3 EXON 1 POLYMORPHISMS COMPROMISE NUCLEAR RE-ENTRY AFTER INFLAMMATION AND SHOW HIGH PREVALENCE IN THE GERMLINE OF PATIENTS WITH INFLAMMATORY AND NEOPLASTIC DISEASE STATES

Background
Colonoscopy withdrawal time (CWT) of at least 6-9 minutes is the minimum time needed for adequate adenoma detection in the general population. The ideal CWT in patients with inflammatory bowel disease (IBD) has not been determined. We aimed to identify the optimal CWT associated with the detection of polypoid dysplasia in patients with IBD.

Methods
This is a single center, retrospective study from 1/1/2017-9/1/2022 of adult patients 18 years of age with IBD in endoscopic healing (absence of erosions/ulcers in Crohn’s disease; Mayo ulcerative colitis (UC) endoscopic sub-score of 0 or 1) undergoing surveillance via high-definition white light colonoscopy. We excluded incomplete colonoscopies, dye-chromoendoscopy exams and patients with previous colonic surgeries. CWT was defined as the time from cecal intubation to withdrawal from the anal canal rounded to the nearest minute. The primary outcome was the association of CWT with the presence of polypoid dysplasia (adenomas and sessile serrated polyps (SSP)) evaluated as a composite outcome. The secondary outcome was to identify an optimal CWT cutoff associated with polypoid dysplasia detection.

Results
A total of 259 patients (mean age 56 ± 14.8 years; 51.3% female, 68% with UC; 8.9% with primary sclerosing cholangitis) underwent 330 colonoscopies. A total of 12 patients (4.6%) had a personal history of invisible dysplasia while 24.7% (n=64) had a history of polypoid dysplasia and 10% had a family history of colorectal cancer. Colonoscopies were performed by IBD specialists in 40.9% (n=135), gastroenterology fellows in 9.7% (n=32) and non-targeted biopsies were obtained in 97.3% (n=321) of colonoscopies performed. The median CWT in the whole cohort was 22 minutes (interquartile range 15-29).

Invisible dysplasia was noted in 2.1% (n=7) while polypoid dysplasia was detected in 17.3% (n=57; 43 adenomas and 16 SSP) of procedures. Baseline characteristics comparing the groups with and without polypoid dysplasia are shown in Table 1. The mean CWT was significantly higher in the polypoid dysplasia group at 32.6 ± 22.3 minutes vs. 22.7 ± 11.1 minutes in procedures without polypoid dysplasia (p=0.002) (Table 1). On multivariable analysis, advanced age (p < 0.001), personal history of adenoma/SSP (p=0.01) and CWT (p <0.001) were independently associated with polypoid dysplasia (Table 2).

A CWT of 15 minutes (odds ratio (OR) 2.71, 95% CI: 1.11-6.6; p=0.02) and not ≥ 9 minutes (OR 2.57, 95% CI: 0.33-20.2; p=0.35) is significantly associated with detection of polypoid dysplasia.

Conclusion
In our cohort of patients with IBD undergoing surveillance via high-definition white light colonoscopy, the mean CWT was independently associated with the detection of polypoid dysplasia. A CWT of at least 15 minutes and not 9 minutes was significantly associated with the detection of polypoid dysplasia.

Background and aims: Colorectal cancer (CRC) incidence rates are increasing among younger adults in the U.S., but little is known about the unique survivorship needs of this population after diagnosis. We estimated risk of second cancers among survivors of early-onset CRC and identified factors associated with risk.
Methods: We identified young adults (age 18-49 years) with stage 0-III CRC diagnosed between 1992-1999 using population-based data from National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program. We estimated cumulative incidence of a second cancer of any type, as well as a second CRC, using the Fine and Gray method to account for the competing risk of death. To illustrate findings, we plotted cumulative incidence curves on both a calendar time and age scale. We also identified patient-, tumor- and treatment-level factors associated with risk of second cancers using hazard regression models, similarly accounting for the competing risk of death. All analyses were stratified by sex.
Results: Among 7,041 persons diagnosed with early-onset CRC, 52.4% were men, 60.5% were non-Hispanic White and 72.6% were 40-49 years old. Of all, 16.2% developed a second cancer, including 337 second CRCs. Accounting for death as a competing event, 25-year cumulative incidence of a second cancer of any type was 18.5% (95% CI 17, 20) for men and 16.8% (95% CI 15, 18) for women (Figure); 25-year cumulative incidence of a second CRC was 6.4% (95% CI 5, 7) for men and 4.4% (95% CI 4, 5) for women. Similarly, by age 70 years, cumulative incidence of a second cancer of any type was 19.7% (95% CI 18, 21) for men and 18.4% (95% CI 17, 20) for women; cumulative incidence of a second CRC was 6.6% (95% CI 6, 8) for men and 4.5% (95% CI 4, 5) for women at age 70 years.
For men, lower county-level median household income (<70K vs. >70K: HR=1.3, 95% CI 1.0, 1.5), higher tumor grade (4 vs. 1: HR=3.9, 95% CI 1.8, 8.4), and histology (mucinous adenocarcinoma vs. non-adenocarcinoma: HR=4.6, 95% CI 1.6, 12.9) were associated with increased risk of second cancer of any type. Among women, higher stage (II vs. 0-I: HR 0.75, 95% CI 0.59, 0.97; III vs. 0-I: HR 0.51, 95% CI 0.39, 0.66) and tumor location (distal vs. proximal colon: HR 0.75, 95% CI 0.60, 0.95; rectum vs. proximal colon: HR 0.5, 95% CI 0.38, 0.65) was associated with reduced risk of second cancer of any type.
Conclusion: One in six persons diagnosed with stage 0-III early-onset CRC will be diagnosed with a second cancer, and most of these second cancers are not CRC. Given these risks, additional studies to inform evidence-based screening and surveillance recommendations in this population are needed.

Background. DNA mismatch repair allows for repair of frameshift mutations that causes microsatellite instability (MSI) associated with a subset of colorectal cancers (CRCs). Elevated microsatellite alterations at select tetranucleotide repeats (EMAST) is a form of MSI that associates with alterations in MSH3 function causing dinucleotide or longer MSI. Germline biallelic loss-of-function MSH3 variants result in a familial polyposis syndrome. A 27 base-pair deletion (△27bp) polymorphism has been described in the polyalanine tract (PAT) within MSH3 exon 1 proximate to its nuclear localization signal (NLS), enhancing MSH3 nuclear-to-cytoplasmic accumulation under conditions of inflammation. △27bpMSH3 attenuates MSH3 nuclear function during oxidative stress, permissive for EMAST. This polymorphism has been shown to be prevalent in a small cohort of patients with ulcerative colitis (UC); prior studies have not examined the variability of MSH3’s PAT across multiple disease states.
Methods. We obtained genomic DNA from subjects in the Michigan Genomics Initiative for genotyping of MSH3 PAT using gel electrophoresis and sequencing. We genotyped 182 healthy controls, 197 UC patients, 199 early onset CRC patients (eoCRC; diagnosed <50 years) and 194 later onset CRC patients (loCRC; diagnosed >50 years). Clinicopathologic data were analyzed for associations with PAT variants. We transfected MSH3-FLAG containing various PAT variants into MSH3-null cells to assess intracellular localization.
Results. Prior genome-wide sequencing data across multiple databases have not shown significant prevalence of △27bp or any other PAT variants of MSH3. Here we identified that in healthy controls, MSH3 PAT variants are abundant, with 37% of subjects having homozygous WTMSH3, 48% having heterozygous WTMSH3 and 15% having no WTMSH3. Interestingly, 18% of UC, 17% of eoCRC and 14% of loCRC patients had no WTMSH3 (p>0.05 vs controls). Advanced CRC patients (stage 3/4) trended higher with no WTMSH3 (17.8% eoCRC, 10.5% loCRC, 15.3% CRC) compared to stage 2 patients (15.4% eoCRC, 5% loCRC, 9.1% CRC; p>0.05). Transfected cells containing the MSH3 △PA and △A12 PAT variants accumulated MSH3 into the cytosol over WTMSH3 (P<0.009).
Conclusions. We discovered that 15% of healthy individuals lack an allele for WTMSH3; that percentage appears to be similar amongst UC and CRC patients. MSH3 PAT variants occur in exon 1 proximate to its NLS compromising its function and attenuating inflammation induced cytosolic MSH3 returning to the nucleus, allowing DNA to potentially accumulate mutations. It is unclear if this has consequences for disease progression as we only observed a trend for advanced staged CRC patients over early staged patients. MSH3 polymorphisms warrant further study to determine the risk of these variants in the development of inflammatory bowel disease and colorectal neoplasia.