dMMR Colorectal Cancer Research Articles

Elevated MUC5AC expression is associated with mismatch repair deficiency and proximal tumor location but not with cancer progression in colon cancer

Mucin 5AC (MUC5AC) is a secreted gel-forming mucin expressed by several epithelia. In the colon, MUC5AC is expressed in scattered normal epithelial cells but can be abundant in colorectal cancers. To clarify the relationship of MUC5AC expression with parameters of tumor aggressiveness and mismatch repair deficiency (dMMR) in colorectal cancer, a tissue microarray containing 1812 colorectal cancers was analyzed by immunohistochemistry. MUC5AC expression was found in 261 (15.7%) of 1,667 analyzable colorectal cancers. MUC5AC expression strongly depended on the tumor location and gradually decreased from proximal (27.4% of cecum cancers) to distal (10.6% of rectal cancers; p < 0.0001). MUC5AC expression was also strongly linked to dMMR. dMMR was found in 21.3% of 169 cancers with MUC5AC positivity but in only 4.6% of 1051 cancers without detectable MUC5AC expression (p < 0.0001). A multivariate analysis showed that dMMR status and tumor localization predicted MUC5AC expression independently (p < 0.0001 each). MUC5AC expression was unrelated to pT and pN status. This also applied to the subgroups of 1136 proficient MMR (pMMR) and of 84 dMMR cancers. The results of our study show a strong association of MUC5AC expression with proximal and dMMR colorectal cancers. However, MUC5AC expression is unrelated to colon cancer aggressiveness.

Pembrolizumab in Microsatellite-Instability–High Advanced Colorectal Cancer

BackgroundProgrammed death 1 (PD-1) blockade has clinical benefit in microsatellite-instability–high (MSI-H) or mismatch-repair–deficient (dMMR) tumors after previous therapy. The efficacy of PD-1 blockade as compared with chemotherapy as first-line therapy for MSI-H–dMMR advanced or metastatic colorectal cancer is unknown.MethodsIn this phase 3, open-label trial, 307 patients with metastatic MSI-H–dMMR colorectal cancer who had not previously received treatment were randomly assigned, in a 1:1 ratio, to receive pembrolizumab at a dose of 200 mg every 3 weeks or chemotherapy (5-fluorouracil–based therapy with or without bevacizumab or cetuximab) every 2 weeks. Patients receiving chemotherapy could cross over to pembrolizumab therapy after disease progression. The two primary end points were progression-free survival and overall survival.ResultsAt the second interim analysis, after a median follow-up (from randomization to data cutoff) of 32.4 months (range, 24.0 to 48.3), pembrolizumab was superior to chemotherapy with respect to progression-free survival (median, 16.5 vs. 8.2 months; hazard ratio, 0.60; 95% confidence interval [CI], 0.45 to 0.80; P=0.0002). The estimated restricted mean survival after 24 months of follow-up was 13.7 months (range, 12.0 to 15.4) as compared with 10.8 months (range, 9.4 to 12.2). As of the data cutoff date, 56 patients in the pembrolizumab group and 69 in the chemotherapy group had died. Data on overall survival were still evolving (66% of required events had occurred) and remain blinded until the final analysis. An overall response (complete or partial response), as evaluated with Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1, was observed in 43.8% of the patients in the pembrolizumab group and 33.1% in the chemotherapy group. Among patients with an overall response, 83% in the pembrolizumab group, as compared with 35% of patients in the chemotherapy group, had ongoing responses at 24 months. Treatment-related adverse events of grade 3 or higher occurred in 22% of the patients in the pembrolizumab group, as compared with 66% (including one patient who died) in the chemotherapy group.ConclusionsPembrolizumab led to significantly longer progression-free survival than chemotherapy when received as first-line therapy for MSI-H–dMMR metastatic colorectal cancer, with fewer treatment-related adverse events. (Funded by Merck Sharp and Dohme and by Stand Up to Cancer; KEYNOTE-177 ClinicalTrials.gov number, NCT02563002.)

Clinicopathological features and types of microsatellite instability in 1394 patients with colorectal cancer

To explore the clinicopathological features and types of genic mutations in DNA mismatch repair (MMR) in colorectal cancer (CRC). Immunohistochemistry was used to determine the expression of MMR proteins in 1394 patients with CRC, and PCR-capillary electrophoresis (PCR-CE) was used to detect microsatellite instability (MSI) in 106 cases of defective MMR (dMMR), 46 cases of proficient MMR (pMMR) with heterogeneous expression and 147 randomly selected cases of pMMR. The relationship between the expressions of MMR proteins and the clinicopathological features of the patients was evaluated. The consistency between the results of immunohistochemistry and PCR-CE was assessed. Immunohistochemical staining showed an incidence of dMMR of 7.6% in the patients. The main type of dMMR was co-deletion of MLH1 and PMS2, accounting for 55.7% of the total dMMR cases. The deletion of MMR proteins was significantly correlated with the patients' age, tumor location, tumor size, gross type, histological type, degree of differentiation, lymph node status and TNM stage (P < 0.05), but not with gender (P > 0.05). The total accordance rate of immunohistochemistry and PCR-CE was 98.7% in these patients. The main type of dMMR is co-deletion of MLH1 and PMS2 in patients with colorectal cancer. dMMR colorectal cancer has typical clinicopathological features and a lower incidence in China than in Western countries. The results of immunohistochemistry and PCR-CE are highly consistent for detecting dMMR in colorectal cancer patients.

Tn Antigen Expression Defines an Immune Cold Subset of Mismatch-Repair Deficient Colorectal Cancer.

Colorectal cancer (CRC) cells often express Tn antigen, a tumor-associated truncated immature O-glycan (GalNAcα-O-Ser/Thr) that can promote tumor progression. Immunotherapies against Tn antigen have been developed and are being evaluated in clinical trials. Tn antigen can also be considered a novel immune checkpoint that induces immunosuppressive signaling through glycan-biding lectins to lead effector T cell apoptosis. We evaluated the correlation of Tn antigen expression by immunohistochemistry with mismatch-repair (MMR) status, tumor-infiltrating lymphocytes, tumor cell PD-L1 expression, and clinicopathological characteristics in 507 CRC patients. Although 91.9% of CRCs showed negative or weak Tn antigen staining (Tn-negative/weak), we identified a small subset of CRCs (8.1%) that displayed particularly intense and diffuse distribution of Tn antigen immunoreactivity (Tn-strong) that closely related to deficient MMR (dMMR). Moreover, 40 dMMR CRCs were stratified into 24 Tn-negative/weak dMMR tumors (60.0%) exhibiting dense CD8+ lymphocyte infiltrate concomitant with a high rate of PD-L1 positivity, and 16 Tn-strong dMMR tumors (40.0%) that demonstrated CD8+ T cell exclusion and a lack of PD-L1 expression, which was comparable to those of proficient MMR. Our finding suggests that the immune cold subset of patients with Tn-strong dMMR CRC may be effectively treated with immune checkpoint blockade therapy or cellular immunotherapy targeting Tn antigen.

Clinicopathological features of mismatch repair protein expression patterns in colorectal cancer

Microsatellite instability (MSI) is reflective of a deficient mismatch repair (dMMR) system, which is mostly associated with the methylation of mismatch repair (MMR) genes and BRAF mutations in sporadic colorectal cancers (CRCs). We performed a retrospective study to analyze the clinicopathological features of dMMR CRCs and their association with the BRAF V600E mutation. The incidence of dMMR CRCs in our cohort was 7.4 % (118/1603). Immunohistochemistry (IHC) revealed four common dMMR IHC patterns in 116 dMMR CRCs from 110 patients. dMMR type 1 (MLH1-/PMS2-) CRCs were the most frequent pattern, usually showing typical proximal location and MSI histology. The BRAF V600E mutation was almost exclusively observed in dMMR type 1 (32 of 72) and dMMR type 2 (PMS- only, 7 of 18) CRCs (p = 0.001). Patients with dMMR type 3 (MSH2-/MSH6-) CRCs were usually diagnosed at younger ages (p < 0.001) and had the strongest family history of Lynch syndrome-associated tumors (p = 0.002). dMMR type 3 CRCs frequently presented at advanced stages (p = 0.005) with perineural invasion (p = 0.021). We also found a significant positive association of dMMR type 1 and type 3 with advanced stages of CRC, whereas dMMR types 2 and 4 (MSH6- only) were usually diagnosed at early stages of CRC (p < 0.001). In conclusion, BRAF V600E mutations almost exclusively occurred in dMMR type 1 and 2 CRCs. Patterns of MMR protein expression display distinct associations with tumor staging and age at diagnosis.

S1688 Dermatomyositis as Initial Presentation of dMMR Colorectal Cancer and Its Treatment Dilemma

S1688 Dermatomyositis as Initial Presentation of dMMR Colorectal Cancer and Its Treatment Dilemma

DNA Mismatch Repair-Deficient Colorectal Carcinoma: Referral Rate for Genetic Cancer Risk Assessment in a Brazilian Cancer Center.

Approximately 15% of colorectal cancers (CRCs) are deficient in DNA mismatch repair proteins (dMMR), a characteristic that can occur in both sporadic and hereditary CRC. Due to sparse studies on dMMR CRC in the Brazilian population, we conducted a retrospective analysis of referral rates for Genetic Cancer Risk Assessment of this population and also describing clinical and molecular characterization of these tumors. A retrospective, longitudinal, and unicenter study that included patients with dMMR CRC detected by IHC analysis from Pathology Database of our institution, from January 2015 to July 2017. MMR IHC testing was performed in 998 CRC tumors, and 78 tumors (7.8%) had dMMR. The mean age at diagnosis was 56.8years (17-90), and most patients were female (41 out of 78, 52.6%). Of the 52 patients with right-sided CRC, 40 tumors (77%) had loss of the MLH1 and/or PMS2 expression, and 12 tumors (23%) had loss of MSH2 and/or MSH6 expression (p = 0.005). From 78 patients with dMMR CRC, only 43 patients (55.1%) were referred for genetic counseling (GC), and of them, only 33 patients (76.7%) really went to GC consultation. A total of 21 patients with dMMR CRC performed genetic testing. Overall, genetic referral was less than expected in our population. Most of dMMR CRC patients did not receive GC, even in a cancer center, either due to the absence of referral or personal decision and few patients who pursued genetic counseling performed genetic testing.

Abstract 740: Improved microsatellite instability detection in endometrial and prostate cancers using long mononucleotide repeat markers

Abstract Microsatellite instability (MSI) assays are used to screen cancer patients with mismatch repair deficiency (dMMR) for immune checkpoint inhibitor therapy. However, short mononucleotide repeat (SMR) markers in current MSI assays may sometimes display subtle shifts that are difficult to interpret in certain dMMR cancers, particular non-colorectal cancers. Long mononucleotide repeat (LMR) markers that are more prone to replication errors may improve the sensitivity of MSI assays. In this study, we compared the performance of SMR and LMR markers using two panels: (1) MSI Analysis System Version 1.2 (Promega) consisting of five SMR markers (21-27 bases in length) and (2) MSI LMR System (Promega) consisting of four SMR markers from the Version 1.2 panel and four LMR markers (52-60 bases in length). We studied 20 MMR proficient (pMMR) and 18 dMMR colorectal cancers (CRC) defined by concordant immunohistochemical staining (IHC) and the Version 1.2 MSI panel, 12 pMMR and 9 dMMR endometrial cancers (EC) defined by IHC alone, and 9 dMMR prostate cancers (PC) defined by loss of MSH2 IHC staining, loss of function MSH2 mutations, and increased mutation frequency. A marker was defined as unstable if a shift of 2 or more bases was observed in the tumor sample when compared to the normal sample. When using the Version 1.2 panel, we defined MSI high (MSI-H) as 2 or more unstable markers, MSI low (MSI-L) as 1 unstable marker, and microsatellite stable (MSS) as no shifts. With the LMR panel, we defined MSI-H as 3 or more unstable markers, MSI-L as 1 or 2 unstable markers, and MSS as no shifts. In dMMR CRC, the clinical sensitivity of the LMR and Version 1.2 panels for MSI were both 100%. In pMMR CRC, MSI-H was not observed in any cases using either panel, but MSI-L was observed in 2 and 0 cases using the LMR and Version 1.2 panels, respectively. In dMMR CRC, the average size of allelic shifts in the four LMR and SMR markers from the LMR panel were 8.7 and 22.1 bases, respectively. Germline polymorphisms were observed in 47% and 1% of LMR and SMR markers, respectively. In dMMR EC, the LMR panel showed greater sensitivity than the Version 1.2 panel (100% vs 89%). In pMMR EC, MSI-H was not observed in any cases using either panel, but MSI-L was observed more often using the LMR panel when compared to the Version 1.2 panel (2 vs 0 cases). In addition, LMR markers displayed larger shifts than SMR markers (12.1 vs 4.9 bases). Polymorphisms were also more frequent in LMR markers relative to SMR markers (60% vs 2%). Likewise, in dMMR PC, the sensitivity of the LMR panel was greater than that of the Version 1.2 panel (89% vs 44%). Furthermore, shifts in LMR markers were larger than those in SMR markers (10.3 vs 3.1 bases), and polymorphisms in LMR markers were more frequent than in SMR markers (33% vs 0%). Overall, LMR markers display greater clinical sensitivity and larger shifts, indicating that LMR markers can improve MSI detection in non-colorectal cancer. Citation Format: John H. Lin, Suping Chen, Liana B. Guedes, Emmanuel S. Antonarakis, Colin C. Pritchard, Tamara L. Lotan, James R. Eshleman. Improved microsatellite instability detection in endometrial and prostate cancers using long mononucleotide repeat markers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 740.

Loss of survival advantage for deficient mismatch repair in patients with advanced colorectal cancer may be caused by changes in prognostic value of CD8+T cell

BackgroundPatients with stage II deficient mismatch repair (dMMR) show a better prognosis than patients with colorectal cancer (CRC) with proficient mismatch repair (pMMR). However, this beneficial effect is decreased in advanced stages of the disease. This study was conducted to investigate the prognostic value of dMMR in different stage and alterations in the tumor microenvironment.MethodsThis was a matched retrospective cohort study. Thirty-two patients with stage III&IV dMMR matched with 32 patients with stage I&II dMMR and 64 patients with pMMR were evaluated. Immunohistochemistry analysis was performed for the 64 patients with dMMR to explore the expression and prognostic effect of CD3, CD4, CD8, and PD-L1.ResultsPatients with stage III–IV dMMR showed no advantage in overall survival (OS) and disease-free survival (DFS) compared to patients with pMMR (P = 0.244, P = 0.667). No expression differences in CD3, CD4, CD8, and PD-L1 at the center of the tumor (CT) or invasive margin (IM) were found between patients with stage I&II and stage III&IV dMMR. High CD3 expression at the CT and high CD3 an CD4 expression at the IM improved both OS and DFS. High CD8 expression showed opposite prognostic value in patients with stage I&II and III&IV dMMR. A similar tendency was observed for PD-L1 expression.ConclusionPatients with stage III–IV dMMR showed no prognostic advantage over patients with pMMR. Expression of CD3, CD4, CD8, and PD-L1 was similar between stage I&II and III&IV dMMR CRC. High CD3 expression at the CT and high CD3 and CD4 expression at the IM can significantly improve patient prognosis. The opposite prognostic tendency of CD8 and PD-L1 for patients with stage I&II and III&IV dMMR may be relevant to CD8+T cell exhaustion and functional changes at inhibitory immune checkpoints.

Different surgical outcome and follow-up status between dMMR and pMMR colorectal cancer patients who fulfilled with Amsterdam-II criteria

BackgroundAlthough hereditary non-polyposis colorectal cancer (HNPCC) could be subtyped into proficient or deficient mismatch repair gene expression (pMMR or dMMR), distinct clinical features between these two subgroups patients were rarely reported.MethodsWe retrospectively analyzed 175 hereditary non-polyposis colorectal cancer (HNPCC) patients between January 1995 and December 2012. Cox proportional hazards model was used to compare the differences between two subgroups.ResultsSignificant differences of disease free survival (DFS) and overall survival (OS) exist between dMMR and pMMR. In addition to other factors including younger mean age of diagnosis for dMMR patients (48.6 years vs. 54.3 years), operation type (more extended colectomy for dMMR 35.8% vs. 14.5%), tumor location (right colon predominance for dMMR 61.7% vs. 27.3% and more rectum cases for pMMR 41.8% vs. 11.7%), tumor differentiation (more poor differentiation for dMMR 23.3% vs. 9.0%), N staging (more N0 cases for dMMR 70.8% vs. 50.9%), more frequently presence of extra-colonic tumors for dMMR (16.7% vs.1.8%), and lower recurrence rates (9.1% vs.35.3%). Significantly different cumulative incidences of developing metachronous colorectal cancer were observed with 6.18 for pMMR patients and 20.57 person-years for dMMR patients (p < 0.001).ConclusionsDistinct clinicopathological features significantly exist between dMMR and pMMR subtypes patient, MMR status should be consider to tailor operation types and follow up surveillance between these two subgroups patients who all fulfilled with Amsterdam-II criteria.

A Model for Predicting DNA Mismatch Repair-deficient Colorectal Cancer.

Identifying patients with DNA mismatch repair-deficient (dMMR) colorectal cancer (CRC) is vital to improve treatment and identify patients with Lynch syndrome (LS). We developed a prediction model for dMMR CRC using clinicopathologic features. We reviewed the medical records of 1,147 patients who underwent resection of stage I-IV CRC in whom universal screening for LS using immunohistochemistry for MMR proteins had performed. Univariate and multivariate logistic regression analyses were used to build a prediction model of dMMR CRC. The prevalence of dMMR CRC was 5.2%. Age (≥75 years), tumor location (right-sided colon), main histologic features (poor differentiation), maximum tumor size (≥65 mm), and stage (I/II) were independent significant variables related to dMMR. We created a formula for predicting the likelihood of dMMR, and the probability ranged from 0.2% to 83%. dMMR CRC can be identified efficiently using clinicopathologic features obtained in daily clinical practice.

Evaluation of yield and experiences of age-related molecular investigation for heritable and nonheritable causes of mismatch repair deficient colorectal cancer to identify Lynch syndrome.

Universal mismatch repair deficiency (dMMR) testing of colorectal cancer (CRC) is promoted as routine diagnostics to prescreen for Lynch syndrome. We evaluated the yield and experience of age‐related molecular investigation for heritable and nonheritable causes of dMMR in CRC below age 70 to identify Lynch Syndrome. In a prospective cohort of 3602 newly diagnosed CRCs below age 70 from 19 hospitals, dMMR, MLH1 promoter hypermethylation, germline MMR gene and somatic MMR gene testing was assessed in daily practice. Yield was evaluated using data from the Dutch Pathology Registry (PALGA) and two regional genetic centers. Experiences of clinicians were evaluated through questionnaires. Participating clinicians were overwhelmingly positive about the clinical workflow. Pathologists routinely applied dMMR‐testing in 84% CRCs and determined 10% was dMMR, largely due to somatic MLH1 hypermethylation (66%). Of those, 69% with dMMR CRC below age 70 without hypermethylation were referred for genetic testing, of which 55% was due to Lynch syndrome (hereditary) and 43% to somatic biallelic pathogenic MMR (nonhereditary). The prevalence of Lynch syndrome was 18% in CRC < 40, 1.7% in CRC age 40‐64 and 0.7% in CRC age 65‐69. Age 65‐69 represents most cases with dMMR, in which dMMR due to somatic causes (13%) is 20 times more prevalent than Lynch syndrome. In conclusion, up to age 65 routine diagnostics of (non‐)heritable causes of dMMR CRCs effectively identifies Lynch syndrome and reduces Lynch‐like diagnoses. Above age 64, the effort to detect one Lynch syndrome patient in dMMR CRC is high and germline testing rarely needed.

Mismatch repair deficiency testing in colorectal cancer and factors associated with nonadherence to guidelines.

e16069 Background: Mismatch repair (MMR) deficiency is characteristic of Lynch syndrome, which typically affects patients &lt; 50 years old with colorectal cancer (CRC) but can also occur in sporadic CRC. MMR deficiency causes microsatellite instability (MSI) and affects therapy response and prognosis. Guidelines now recommend universal testing of MMR/MSI in all CRC patients, but universal testing has not been achieved. Our study sought to evaluate factors associated with MMR/MSI testing in CRC patients. Methods: The National Cancer Database (NCDB) identified 433,968 patients diagnosed with stages I-IV CRC from 2011-2016. Variables included gender, race, stage, insurance status, education, income, and treatment facility type. Baseline characteristics were compared using Pearson's chi‐square test between patients not tested versus tested for MMR/MSI status. Multivariate logistic regression analysis determined the factors associated with increased probability of MMR/MSI testing. Results: Only 34.7% patients were tested for MMR/MSI and those £ 40 years old were more likely to be tested as were Caucasian patients. Patients with private insurance were more likely to be tested compared to uninsured (OR 1.21; 95% CI 1.1601.27, p &lt; 0.001). Testing also correlated with increasing education, reported as the percentage of adults over 25 years old who did not graduate high school within a zip code. Diagnosis at an academic/research program was also a positive predictor of MMR/MSI testing compared to a community program (OR 1.74; 95% 1.71-1.77, p &lt; 0.001). Testing was dependent on stage with the greatest likelihood of testing in stage II (OR 1.44, 95% CI 1.41-1.46, p &lt; 0.001) and the least in stage IV (OR 0.72; 95% CI 0.71-0.74, p &lt; 0.001) compared to stage I. Still, the trend for testing increased over the years (trend p &lt; 0.001), with that in 2016 being 4 times more likely than in 2011 (OR 4.66; 95% CI 1.53-4.80, p &lt; 0.001). Conclusions: Our study identified established risk factors affecting care such as African American race, treatment at a non-academic facility and being uninsured. It also showed age and stage were factors associated with noncompliance to new guidelines regarding testing for MMR/MSI with testing being less frequent in older patients and those with later stages. An explanation and study limitation is that NCDB only collected diagnoses until 2016 while immunotherapy in MSI-H or dMMR CRC was approved in 2017. With more treatment options available now to these patients, testing rates will hopefully improve with more research needed to capture this.

Landscape of germline mutations in 1144 patients (Pts) with gastrointestinal (GI) cancers.

e13660 Background: The efficacy of PARP inhibitors in germline BRCA-mutated pancreatic adenocarcinoma (PC) and immune checkpoint inhibitors in dMMR colorectal cancer (CRC) shows the importance of genetic testing. We aimed to characterize the frequency of pathogenic/likely pathogenic germline variants (PLPVs) in GI cancer pts. Methods: A retrospective review of pts referred to the Levine Cancer Institute Genetics Program was conducted. Genetic testing used a focused hereditary cancer 4-43 gene panel or pan-cancer 82-84 gene panel. Results: Out of 1144 GI cancer pts seen between 2010 and 2019, 869 underwent germline testing, and 199 (23%) pts had at least one PLPV in a hereditary cancer susceptibility gene, while 253 (29.3%) had a variant of uncertain significance. Of 630 CRC pts, 24% had a PLPV and 13% harbored a germline mutation in DNA MMR genes and were diagnosed with Lynch Syndrome, representing ~50% of all pts with a PLPV. Other germline PLPVs were found in APC, ATM, BRCA1, BRCA2, CHEK2, MUTYH, and PALB2. Of 163 PC pts, 16.6% had a PLPV in ATM, BRCA2, CDKN2A, and MEN1. Gastric cancer pts (17%) had germline PLPVs in APC, BRCA2, CDH1, MLH1, and MSH2; biliary cancer pts (17%) had germline PLPVs in PALB2, RAD50, and PTCH1; and GIST pts (60%) had PLPVs in SDHA or SDHB. Conclusions: Germline mutations were found in 23% of GI cancer pts, underlining the importance of multigene germline testing. Knowledge of inherited GI cancer risk helps determine the likelihood of benefit from possible specific targeted therapies. Genetic testing and counseling pose a challenge, but implications for pts with hereditary syndromes are highly significant. [Table: see text]

Effect of TP53 mutation on antitumor immunity and responsiveness to immunotherapy in colorectal cancer.

e16014 Background: Although we have approved immune checkpoint inhibitors (ICIs) in microsatellite instability high (MSI-H) or mismatch-repair-deficient (dMMR) colorectal cancer (CRC), more than half of patients did not respond well to ICIs, emphasizing the need for effective biomarkers. Methods: Whole exome sequencing (WES) analysis was performed on a Chinese cohort of MSI-H/dMMR CRC patients (n = 16). We investigated the pertinence between clinic benefit and potential biomarkers, as TP53 mutation and tumor mutational burden (TMB). The open cohort of ICI-treated CRC patients from the Memorial Sloan Kettering cancer center (MSK ICI cohort) further validated the genomic correlation. Besides, we used the colorectal adenocarcinoma (COADREAD) cohort from The Cancer Genome Atlas (TCGA) dataset to explore the effect of TP53 mutation on the genomic and immunogenetic features. Results: In a Chinese cohort of MSI-H/dMMR CRCs receiving ICIs, we found that patients with TP53 mutation (6 out of 16) showed a remarkable lower durable clinic benefit (DCB) rate than TP53 wild-type subgroup (100% vs. 33%, P = 0.008). Moreover, TP53 wild-type patients were associated with prolonged progression-free survival (P = 0.02; HR, 0.11) and overall survival (P = 0.0037; HR, 0.04). However, TMB-high revealed no statistical significant predictive or prognostic value when using top 20%, 40% or 50% as the cutoff values in our cohort. Further, in order to confirm our observation, we analyzed the association of TP53 mutation with clinic outcome in the publicly available MSK ICI-treated CRC cohort. As expected, the TP53 wild-type patients had a better prognosis (P = 0.037; HR, 0.54) versus the TP53 mutant subgroup. Mechanically, we found that the retention of wild-type TP53 in the TCGA COADREAD cohort was associated with improvement of several steps in the cancer immunity cycle. More intriguingly, in the MSI-H subtype, the TP53 wild-type tumors showed enhanced recognition of cancer cells by T cells and a higher proportion of effector memory CD8+ T cells. Finally, TP53 wild-type tumors also showed reduced heterogeneity and decreased burden of copy number variation, but the correlation between TP53 wild-type tumors and TMB was limited due to MSI status. Conclusions: Our study highlights that TP53 mutations in CRC may indicate inhibition of the tumor microenvironment, particularly in MSI-H/dMMR CRCs. Therefore, the assessment of TP53 status may have important significance in predicting the effectiveness of ICIs in CRC patients and their MSI-H /dMMR subgroup.

Low prevalence of mismatch repair deficiency in Chinese colorectal cancers: a multicenter study.

BackgroundAlthough universal testing for mismatch repair deficiency (dMMR) has been recommended to all colorectal cancer (CRC) patients, related evidence for the Chinese population is lacking. Here, we investigated the prevalence and clinicopathological features of dMMR patients in a large Chinese CRC cohort.MethodsWe included 7,373 CRC patients treated at four Chinese medical centers between August 2010 and September 2016. Patients’ baseline characteristics and pathological features were recorded. The clinicopathological features were compared between patients with MLH1/PMS2 deficiency (dMLH1/PMS2) and MSH2/MSH6 deficiency (dMSH2/MSH6).ResultsAmong the investigated patients, 654 (8.9%) were identified with dMMR CRCs and, of them, 401 (61.3%) were males, with a median age of 55 years (range, 22–87 years); 355 (54.3%) had stage II CRC based on American Joint Committee on Cancer 8th edition. The prevalence of the dMLH1/PMS2 group and the dMSH2/MSH6 group were 51.5% (337/654) and 25.1% (164/654), respectively. Compared with dMSH2/MSH6 patients, those with dMLH1/PMS2 were older (57 vs 52 years, P < 0.001), more likely to be female (45.7% vs 31.5%, P = 0.004), prone to having tumors located in the right-hand side of the colon (59.0% vs 47.6%, P = 0.015), and less likely to have a family history of tumors (29.7% vs 43.3%, P = 0.003).ConclusionsThe prevalence of dMMR in Chinese CRC patients was low, especially in the dMLH1/PMS2 group. The clinicopathological features were different between dMMR subgroups.

Clinically applicable cases of anti-programmed cell death protein 1 immunotherapy for colorectal cancer patients.

We investigated the prevalence and characteristics of defective mismatch repair (dMMR) in colorectal cancer (CRC) patients who would potentially benefit from anti-programmed cell death protein 1 (PD-1) immunotherapy. Medical records were obtained and reviewed for 1147 patients who underwent surgical resection of stage I-IV CRC, in whom universal screening for Lynch syndrome using immunohistochemistry for MMR proteins had been undertaken. The molecular characteristics of dMMR CRCs were also investigated. Defective MMR accounted for 5.2% of stage I-IV CRC patients, including 12 (1.0% of all CRC patients) who had stage IV disease or recurrence after curative resection (n = 6 each). These 12 patients included patients with LS (n = 3) and Lynch-like syndrome (n = 1). Defective MMR tumors were predominantly located in the right-sided colon (P < 0.01). Approximately 1% of stage I-IV CRC patients could potentially benefit from anti-PD-1 immunotherapy, while one-third would require genetic counseling and/or MMR gene testing.

Microsatellite Stable Colorectal Cancer With an Immunogenic Phenotype: Challenges in Diagnosis and Treatment

BackgroundPatients with deficient microsatellite mismatch repair (dMMR) colorectal cancer (CRC) may respond to immune checkpoint inhibition (ICI), whereas patients with microsatellite-stable (MSS) CRC have not demonstrated response. However, a proportion of MSS tumors display histomorphologic features characteristic of dMMR tumors consistent with an increased antigenicity. Therefore, a subset of patients with CRC not currently receiving ICI treatment may derive benefit from ICI therapy. We review tumors in which the histologic features suggestive of dMMR were in disagreement with the DNA mismatch repair proteins obtained by immunohistochemistry (IHC). Possible causes of such disagreement are discussed. Materials and MethodsThree patients with CRC suggestive of histomorphologic immunogenicity underwent evaluation by IHC staining for mismatch repair (MMR) status, next-generation sequencing assays, and/or polymerase chain reaction. ResultsFindings compatible with an immunogenic response were similarly observed in all patients. Case 1 highlighted the limiting factors inherent to IHC staining for MMR status: a biopsy initially interpreted as MSS was subsequently interpreted as being dMMR. Case 2 examined the challenges in reconciling histologic characteristics traditionally associated with dMMR CRCs but ultimately determined to be MSS. Case 3 examined the microsatellite instability of CRC resulting from MLH1-methylation and/or MSH6 mutation. ConclusionsWe demonstrated the challenges in establishing MMR status when confronted with conflicting results from histology, IHC, polymerase chain reaction, and next-generation sequencing. Given that dMMR status has been shown to be a biomarker for ICI responsiveness, the importance of accurate identification is critical.

Clinical and molecular markers of immune checkpoint inhibitor (ICI) response in dMMR colorectal cancer (CRC) patients (pts).

225 Background: ICIs induce durable responses in dMMR CRC patients. However, clinical and molecular biomarkers of response to ICIs have not been well-established. In this study, we investigated impact of specific MMR gene loss, BRAF V600E mutation and clinical characteristics of pts on clinical outcomes of ICIs. Methods: Pts were eligible if they had confirmed dMMR CRC by IHC or MSI-H by PCR and received ICIs between 01/01/2012 and 05/01/2019 at Winship Cancer Institute of Emory University, Mayo Clinic, Vanderbilt or Stanford University. Due to the functional dependency, the groups were categorized as protein loss of MLH1+PMS2 vs MSH2+MSH6. Log-rank test, Cox hazard model and Fisher’s exact test were used for survival outcomes, the best response and the distribution of variables among the subgroups. Results: A total of 66 pts with dMMR CRC were identified and BRAF status was available for 41 pts. ORRs in MLH1+PMS2 and MSH2+MSH6 groups were 72.9% and 56.5% respectively (P = 0.189). At 2 years, PFS rates were 55.6% and 78.2% for MLH1+PMS2 and MSH2+MSH6 groups respectively (P &lt; 0.001). Pts with BRAF V600E mutations had significantly worse outcomes as compared to pts with wild-type BRAF (2-year PFS rate of 35.0% and 73.3% respectively; P &lt; 0.001). Notably pts &lt; 65 had better 2-year disease control rates when compared to &gt; 65 (71.1% and 41.5% respectively; P &lt; 0.001). We also observed worse 2-year PFS rates in pts with liver metastases (P = 0.014). CRC side and tumor volume did not impact 2-year PFS rates in our cohort. Conclusions: Our data suggest that pts with loss of function in MSH2+MSH6 may have better 2 year-PFS rates compared pts with MLH1+PMS2 even though ORR favored MLH1+PMS2 group suggesting that ORR may not reflect the durability of ICI response in dMMR CRC patients. Consistently, pts with BRAF V600E mutation which is associated with MLH1 promoter methylation had significantly worse 2-year PFS rates. Overall, our findings suggest that BRAFV600E mutation, the affected MMR proteins, pt age, and site of metastasis may impact durability of ICI response in dMMR CRC patients.

Predicting CD8+ T-cell infiltration in colorectal cancer using versican proteolysis across molecular profiles.

189 Background: The clinical indications for immunotherapies continue to increase across cancer types. In colorectal cancer (CRC), there has been little progress in the use of these therapies outside of mismatch repair deficient cancers (dMMR). However, even in dMMR cancers only a minority actually respond to the FDA-approved anti-PD1 agents. The tumor microenvironment is increasingly implicated in the resistance of cancers to immune-based therapies. Our group has previously described that accumulation of a matrix proteoglycan, versican, correlates with a reduction in CD8+ T-cell infiltration in CRCs, while proteolysis of versican, releasing the bioactive fragment versikine, correlates with increased infiltration. Here we examine the impact of pathogenic mutations on the utility of MMR status and versican proteolysis to predict CD8+ T-cell infiltration. Methods: Matched normal colon and CRC tissues from 122 patients were stained for versican, versikine, MLH1, MSH2, MSH6, PMS2, CNNB1, and CD8. Each was reviewed by a blinded GI surgical pathologist and CD8 quantified as tumor infiltrating lymphocytes (TILs) per high power field (hpf). 107 of the CRC samples were available for sequencing using the Qiagen Comprehensive Cancer Panel examining 160 genes across cancer relevant hotspots. The molecular profile was correlated with the IHC staining. Results: As previously reported, dMMR tumors had higher CD8+ T-cell infiltration. This trend persisted across dMMR genotypes (dMMR vs proficient (p)MMR p = 0.0016). Versican proteolysis correlated with increased CD8+ T cell infiltration in dMMR and pMMR cancers and was present in cancers with/without APC, TP53, and KRAS mutations. Across common mutations, cancers with the versican proteolysis predominant phenotype had more CD8+ T-cell infiltration than those without (APC mutant (mt): 11.82 vs 1.97 CD8+ TILs/hpf, p &lt; 0.001; KRAS mt: 9.39 vs 3.08, p = 0.15; BRAF mt: 25.00 vs 7.50, p = 0.13; TP53 mt: 8.61 vs 1.63, p &lt; 0.001). Conclusions: Across common mutations, versican proteolysis predicts CD8+ T-cell infiltration in both dMMR and pMMR CRC. Further investigation into whether this increase in infiltration will lead to greater immunotherapy response is warranted.