MSI-H Colorectal Cancer Research Articles

Spontaneous regression of transverse colon cancer with high-frequency microsatellite instability: a case report and literature review

BackgroundSpontaneous regression (SR) of colorectal cancer (CRC) is extremely rare, and only few cases have been reported. Although it is not yet clarified, a plausible mechanism for SR of CRC is an immunological event.Case presentationIn this report, we present the case of SR of primary CRC in a 78-year-old man. Preoperative colonoscopy was performed, and a type 2 tumor measuring 30 mm in diameter in the transverse colon was detected. The biopsy revealed a poorly differentiated adenocarcinoma. Colectomy was performed 2 months after initial colonoscopy. During the surgery, only a 10-mm ulcer harboring a polypoid lesion measuring 8.5 mm was detected in the resected tissue; no other masses or carcinoma cells were seen on histological examination. Afterwards, the biopsy specimens were reanalyzed, and immunohistological analysis verified this as adenocarcinoma with stroma-infiltrating lymphocytes. Further analysis revealed a loss of two mismatch repair proteins, suggesting sporadic high-frequency microsatellite instability (MSI-H).ConclusionAccording to previous literature, a common site of SR in CRC is the proximal colon, which is a feature of MSI-H CRC. However, our report showed a rare case of SR of CRC, which was in the transverse colon, with MSI-H present. This report indicates a relationship between immunological features of MSI-H and the occurrence of SR of CRC. A better understanding of this phenomenon and the mechanisms involved will have significant preventive and therapeutic implications for CRC, including anti-PD-1 immune checkpoint inhibitor therapy.

Somatic Mutations and Intratumoral Heterogeneity of MYH11 Gene in Gastric and Colorectal Cancers.

MYH11 functions as a contractile protein, converting chemical energy into mechanical energy through adenosine triphosphate hydrolysis. In cancers, an oncogenic fusion CBFB/MYH11 and frameshift mutations have been reported. Truncating mutants of MYH11 exhibited increased ATPase and motor activity, suggesting their roles in energy balance and movement of cancer cells. MYH11 gene has a mononucleotide repeat (C8) in the coding sequences that could be a mutational target in the cancers exhibiting microsatellite instability (MSI). We analyzed the C8 repeat in 79 gastric cancers (GCs) and 124 colorectal cancers (CRCs) including 113 high MSI (MSI-H) and 90 microsatellite stable/low MSI cases. We detected MYH11 frameshift mutations in 4 (11.8%) GCs and 17 (21.5%) CRCs with MSI-H (21/113, 18.6%), but not in microsatellite stable/low MSI cancers (0/90) (P<0.001). We also analyzed intratumoral heterogeneity (ITH) of the MYH11 frameshift mutations and found that 10 of 16 CRCs (62.5%) harbored the regional ITH. Our results show that MYH11 gene harbors somatic frameshift mutations mostly associated with mutational ITH, which together may be features of MSI-H GCs and CRCs. Practically, the data suggest that multiregional analysis is needed for a better evaluation of mutation status in MSI-H tumors to overcome ITH.

FDA grants accelerated approval to ipilimumab for MSI-H or dMMR metastatic colorectal cancer

FDA grants accelerated approval to ipilimumab for MSI-H or dMMR metastatic colorectal cancer

Prognostic impact of BRAF V600E mutation in patients with non-metastatic colorectal cancer with microsatellite instability: A systematic review and meta-analysis.

3597Background: Colorectal cancer (CRC) displaying high levels of microsatellite instability (MSI-H) has been associated with improved survival in colorectal cancer. MSI-H CRC is also known to be e...

Updates on immunotherapy for colorectal cancer

Despite significant advances in standard of care therapies, the 5-year survival rate for metastatic colorectal cancer (CRC) remains around 12%. Immunotherapy has not provided the stellar advances in colorectal cancer that has been seen in other malignancies. Immunotherapy appears to play a pivotal role in microsatellite unstable CRC tumors where the response rates are profound. These results have led to FDA approval of pembrolizumab for MSI-H CRC tumors. Additional research into several new immune agents including IDO inhibitors, vaccine therapy and combinatorial agents are being evaluated for CRC. This review will provide an overview of the approaches currently being investigated.

PD-L1 expression in colorectal cancer defines three subsets of tumor immune microenvironments.

ObjectivesWe investigated the PD-L1 expression in colorectal cancer (CRC) and in its microenvironment.ResultsPD-L1 was expressed in neoplastic cells (NCs) and tumor-infiltrating immune cells (IICs). All samples PD-L1+ on NCs were also on IICs. Three types of cancers could be grouped: group A(NCs-/ IICs-); group B (NCs-/ IICs+); group C (NCs+/IICs+). To group A belong tumors characterized by poorly immunogenic competence, poor immune response but massive granulocyte infiltrate, justifying the absence of PD-L1 as an immunoinhibitor receptor. To Group B probably belong more immunogenic CRCs, justifying the strong IICs-mediated immune response, and up-regulation of PD-L1 expression only on IICs. To group C belong CRCs probably characterized by a large amount of tumor neoantigens resulting in a marked infiltration of lymphocytes and PD-L1 upregulation also in NCs.Materials and MethodsSixty-three colorectal cancer specimens from a cohort of 61 patients were retrospectively reviewed. Thirty-seven MSS and 26 MSI-H CRCs enrolled in this study. Immunohistochemical staining to PD-L1 was performed by using MAb E1L3N.ConclusionsOur study calls attention to the importance to assess PD-L1 expression in tumor microenvironment also evaluating type and density of infiltrating immune cells to better stratify CRCs with different immunological patterns.

Abstract A012: Humanized patient-derived xenografts (PDXs) recapitulate clinical responses in microsatellite stable (MSS) and unstable (MSI-H) colorectal cancer (CRC)

Abstract Introduction: Recent data have demonstrated that patients with MSI-H metastatic CRC are more likely to respond to a PD-1 inhibitor as a single agent compared to patients with MSS CRC. Effective immunotherapy approaches for MSS CRC remain a critical unmet need. There is great interest in investigating immune checkpoint inhibition in combination with novel agents, but preclinical studies have been hampered by current models. To gain a better understanding of immune responses and facilitate preclinical evaluation of combination strategies with immunotherapy, we developed a “hematopoietic” humanized mouse model with the intent of leveraging this model for the development of rational combinations in MSS CRC patients. Methods: BRGS (in house breeding) newborn pups were transplanted with CD34+ cells purified from (HLA unmatched) umbilical cord blood at 48 hours. In order to better understand the immune context of these novel animal models, we selected an MSI-high CRC (MDA-C0999-203) and a MSS (CRC172) humanized PDX model. At 16 weeks, MDA-C0999-203 (MSI-H) and CRC172 (MSS) were implanted on both flanks of humanized mice and nonhumanized controls. When the average tumor size reached ~150-300 mm3, both groups of mice were randomized into vehicle and nivolumab (30mg/kg IP twice weekly) stratified by % chimerism (human CD45+ &amp;gt;45%). At the end of the treatment, a portion of the tumor was immediately fixed in formalin for immunohistochemistry and pharmacodynamic analyses with seven-color multispectral imaging using the Perkin Elmer Vectra- 3 instrument, and compared to a surgical specimen from an untreated patient with an MSI-H tumor. Results: In the MSI-H model we observed tumor growth inhibition in the nivolumab-treated, humanized mice with respect to the humanized vehicle-treated control and the nonhumanized nivolumab-treated group (TGII 3.5% vs 76%). In a separate experiment, an MSS CRC humanized PDX model (CRC172) was treated with nivolumab as described above. Although initial control of tumor growth was observed, this was followed by rapid tumor progression (TGII 138.4%). In addition to flow cytometry, an MSI-H CRC tumor directly from a patient was stained for a variety of immunologic markers and analyzed by Vectra. The tumors contained both CD4- and CD8-positive cells, indicating T-cell infiltration. These data are consistent with what was observed by flow cytometry. Similar results were observed in an MSI-H CRC tumor grown as a xenograft in humanized mice both with and without nivolumab. However, in the MSS CRC PDX model, very few CD4 and CD8 cells were observed in the tumor or in the surrounding stroma. Conclusions: We have successfully established in vivo MSI-H and MSS humanized CRC PDXs. All mice were highly chimeric and the MSI-H model demonstrated high TILs, and responding tumors exhibited IFNγ production, high CD8%, higher effector memory % (HLADR+, CD45RO+), and decreased PD-L1 expression by flow cytometry. Interestingly, we also observed greater numbers of T cells in the lymph nodes of the MSI-H PDX. Moreover, immune infiltrates were observed in the MSI-H PDX compared to the MSS by immunohistochemistry. These data suggest that humanized PDX models may be useful in the development of rational combinations of immunotherapy. Citation Format: Anna Capasso, Julie Lang, Todd M. Pitts, Christopher H. Lieu, Scott Kopetz, Sarah L. Davis, Kimberly Jordan, Stacey M. Bagby, Wells A. Messersmith, Roberta Pelanda, S. Gail Eckhardt. Humanized patient-derived xenografts (PDXs) recapitulate clinical responses in microsatellite stable (MSS) and unstable (MSI-H) colorectal cancer (CRC) [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A012.

Clinical significance of programmed cell death-ligand 1 expression and the immune microenvironment at the invasive front of colorectal cancers with high microsatellite instability.

Immunotherapy is reportedly effective in colorectal cancers (CRCs) with high microsatellite instability (MSI-H); however, the specific cell types that respond to immune checkpoint therapy are unclear. Herein, we aimed to examine the expression of programmed cell death-ligand 1 (PD-L1) and related proteins in MSI-H and microsatellite-stable (MSS) CRCs to investigate the immune microenvironment at the tumor's invasive front. The MSI status was retrospectively assessed in 499 patients undergoing surgical resection of primary CRC; of these, 48 were classified as MSI-H. Propensity score matching was performed, and tissues from 36 and 37 patients with MSI-H and MSS CRCs, respectively, were immunohistochemically evaluated for PD-L1, PD-1, CD8 and CD68. PD-L1 expression was evaluated separately for tumor cells (PD-L1 [T]) and tumor-infiltrating myeloid cells in the stroma (PD-L1 [I]). PD-L1 (T) was positive in only 5.4% and 36.1% of MSS and MSI-H CRCs, while PD-L1 (I) was positive in 27% and 72.2% of these CRCs, respectively. The PD-L1 (T) and PD-L1 (I) expression levels in MSI-H CRCs significantly correlated with poor differentiation, lymphatic invasion and vascular invasion (p < 0.05), and with early-stage adenocarcinoma and high budding grade (p < 0.05), respectively. Significantly more PD-L1 (I), CD8-positive cells and CD68-positive macrophages were present at the invasive front than in the central tumor in MSI-H CRCs (p < 0.005). PD-L1 was expressed on both tumor cells and CD68/CD163-positive (M2) macrophages at the invasive front of MSI-H CRCs. In conclusion, PD-L1-positive tumor cells and M2-type tumor-associated macrophages may contribute to tumor invasion and immune escape at the invasive front.

FDA grants nivolumab accelerated approval for MSI-H or dMMR colorectal cancer

FDA grants nivolumab accelerated approval for MSI-H or dMMR colorectal cancer

Abstract CT119: CPI-444, an oral adenosine A2a receptor (A2aR) antagonist, demonstrates clinical activity in patients with advanced solid tumors

Abstract Background: Accumulation of extracellular adenosine in the tumor microenvironment activates A2aR suppressing anti-tumor immunity. CPI-444 is an oral, selective A2aR antagonist with single agent (SA) antitumor efficacy in mouse models, and the addition of anti-PD-1/PD-L1 antibodies leads to synergistic anti-tumor activity. CPI-444 was well-tolerated in previous clinical trials in the non-oncology setting. This phase 1/1b open-label clinical trial uses a 2-step adaptive design to evaluate CPI-444 alone and in combination with atezolizumab (atezo, Tecentriq®) in patients(pts) with advanced cancers. Preliminary efficacy and safety results in the dose selection phase (Step 1) are reported. This is the first report of adenosine inhibition as a treatment for cancer. Methods: Adult pts who have failed up to 5 standard therapies with advanced solid tumors were enrolled. In Step 1, pts were randomized 1:1:1:1 to 1 of 4 dose cohorts (28 days/cycle) including 3 SA cohorts (100mg BID x 14 days(d), 100mg BID x 28d and 200 mg QD x 14d) or combined with atezo (CPI-444 50mg or 100 mg BID x 14d + atezo 840mg IV q2 weeks). Primary objectives: safety and efficacy and defining the optimal dose and schedule of CPI-444. Results: 48 pts were enrolled in Step 1; 47 received treatment. Median age was 65 years (range, 36-84).Tumor types enrolled were: non- small cell lung cancer(NSCLC, n=10), triple negative breast cancer (TNBC,n=10),melanoma(MEL,n=7), urothelial bladder cancer(UBC,n=6), renal cell cancer(RCC,n=5), MSI-H colorectal cancer(CRC,n=4), head and neck cancer (SCCHN, n=3)and prostate cancer (n=2). Median number of prior systemic regimens was 4(range, 1-5). Twenty-four pts received prior anti PD-1/PD-L1 therapy. One pt in the combination cohort had reversible grade 3 autoimmune hemolytic anemia which was the only DLT observed. Biomarker analyses defined the optimal dose of CPI-444 as 100 mg bid x 28 days. With a median follow-up time of 12 weeks(range, 2-32), the overall disease control rate (DC defined as CR, PR or SD) was 45% per RECIST. Nineteen pts had SD;15 pts received SA CPI-444. Two pts had a PR; both received SA. Of 5 RCC pts enrolled, 4 had DC (1 PR, 3 SD). Of these 4 RCC pts, 3 are receiving SA CPI-444 including the patient with PR. These 4 RCC pts remain on treatment with 2 pts on treatment for &amp;gt; 30 weeks. Of 7 MEL pts, 1 pt receiving SA had a PR and 2 had SD. SD was observed in 5/10 NSCLC pts, 4/10 TNBC pts, as well as 2/6 UBC pts and 1 pt each with CRC, SCCHN and prostate cancer. The proportion of pts with DC were similar for pts treated with CPI-444 alone and for pts treated with CPI-444 combined with atezo. 9/18(50%) pts who were naïve to anti-PD-1/PD-L1 treatment achieved DC as well as 10/24(42%) of pts who were resistant/ refractory to anti-PD1/PDL1 therapy. The most common (≥ 10% of pts) adverse events related to study drug were Grade 1 or 2 nausea (13%) and fatigue (19%). Conclusion: Inhibition of adenosine signaling through the A2aR results in anti-tumor activity in pts with advanced solid tumors. Responses are observed in multiple histologies both as a SA and in combination with atezo and in pts naïve or resistant/refractory to anti-PD-1/PD-L1 therapy. The optimal dose is 100 mg bid continuous. Enrollment in Step 2, evaluating disease-specific cohorts, is ongoing. Citation Format: Leisha Emens, John Powderly, Lawrence Fong, Joshua Brody, Patrick Forde, Matthew Hellmann, Brett Hughes, Shivaani Kummar, Sherene Loi, Jason Luke, Daruka Mahadevan, Benjamin Markman, Ian McCaffery, Richard Miller, Ginna Laport. CPI-444, an oral adenosine A2a receptor (A2aR) antagonist, demonstrates clinical activity in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT119. doi:10.1158/1538-7445.AM2017-CT119

Association of activin type II receptor mutation with microsatellite instability in gastric cancer.

e23191 Background: Microsatellite instability-high status (MSI-H) and alterations in the DNA mismatch repair pathway associate with the efficacy of 5-FU and immune checkpoint inhibitors in patients with gastrointestinal cancers. The activin type II receptor (ACVR2) that binds to the transforming growth factor beta superfamily of ligands is frequently mutated in MSI-H colorectal cancer. However, the incidence of ACVR2 mutations in gastric cancer patients remains unclear. The aim of this study is to reveal the incidence and to examine the association between the MSI-H and ACVR2A mutations in gastric cancer patients. Methods: 124 archived FFPE gastric cancer tissues (stage I-IV), who were operated at Niigata University Medical and Dental Hospital or Niigata Cancer Center Hospital, were analyzed for ACVR2A mutation and MSI status with the NGS-based comprehensive genomic test platform. Clinicopathological characteristics of the patients were also examined. Results: All 124 gastric cancer patients were successfully analyzed. 13 out of 124 patients (10.4%) showed MSI-H status. Interestingly, 10 of 13 MSI-H patients (76.9%) showed ACVR2A mutation, where none (0%) was found among patients with microsatellite stable status (P &lt; 0.001), indicating the strong association between ACVR2A mutation and MSI status in gastric cancer patients. In the ACVR2A mutated group, there was a female predominance (P &lt; 0.05), and cancers of the lower part of the stomach were more common (P &lt; 0.05), compared with the wild type group. Only one of 10 patients with ACVR2A mutation died, and the patients with ACVR2A mutation show a 5-year overall survival rate of 90%. No statistically significant difference in survival was achieved between patients with ACVR2A mutation and wild type; this is probably due to the small number of patients. Conclusions: 10 of 13 MSI-H patients showed ACVR2A mutation. Our results indicate a strong association between ACVR2A mutation and MSI-H in gastric cancer patients.

Clinical course and outcome of patients with high-level microsatellite instability cancers in a real-life setting: a retrospective analysis.

BackgroundThe prognostic and predictive significance of the high-level microsatellite instability (MSI-H) phenotype in various malignancies is unclear. We describe the characteristics, clinical course, and outcomes of patients with MSI-H malignancies treated in a real-life hospital setting.Patients and methodsA retrospective analysis of MSI-H cancer patient files was conducted. We analyzed the genetic data, clinical characteristics, and oncological treatments, including chemotherapy and surgical interventions.ResultsClinical data of 73 MSI-H cancer patients were available. Mean age at diagnosis of first malignancy was 52.3 years. Eight patients (11%) had more than four malignancies each. Most patients (76%) had colorectal cancer (CRC). Seventeen patients (23%) had only extracolonic malignancies. Eighteen women (36%) had gynecological malignancy. Nine women (18%) had breast cancer. Mean follow-up was 8.5 years. Five-year overall survival and disease-free survival of all MSI-H cancer patients from first malignancy were 86% and 74.6%, respectively. Five-year overall survival rates of stage 2, 3, and 4 MSI-H CRC patients were 89.5%, 58.4%, and 22.9%, respectively.ConclusionAlthough the overall prognosis of MSI-H cancer patients is favorable, this advantage may not be maintained in advanced MSI-H CRC patients.

Metastatic Pattern of Stage IV Colorectal Cancer with High-Frequency Microsatellite Instability as a Prognostic Factor.

A recent clinical trial on the immune check-point inhibitor pembrolizumab demonstrated that microsatellite instability (MSI) is a good biomarker for response to this inhibitor. However, clinicopathological features of advanced colorectal cancer (CRC) with high-frequency MSI (MSI-H) are unclear. A total of 2,439 surgically resected CRC tissues were analyzed for MSI status, and mutational status of V-Ki-Ras2 Kirsten rat sarcoma 2 viral oncogene homolog (KRAS), neuroblastoma RAS viral oncogene homolog (NRAS) and v-Raf murine sarcoma viral oncogene homolog B (BRAF). Stage IV cases were selected, and clinical and molecular features were evaluated. There was no significant survival difference observed between MSI-H CRC and microsatellite-stable (MSS) CRC in patients with stage IV disease (3.92 vs. 2.50 years; p=0.766). However, hematogenous and lymphogenous metastasis-dominant CRC with MSI-H demonstrated poor prognosis, whereas peritoneal metastasis-dominant CRC with MSI-H demonstrated good prognosis, (1.33 vs. 5.2 years; p=0.006). Prognosis of stage IV CRC with MSI-H depended on the metastatic pattern. These findings provide useful information for the adaptation of CRC immunotherapy.

BRAF-Mutated Colorectal Cancer Exhibits Distinct Clinicopathological Features from Wild-Type BRAF-Expressing Cancer Independent of the Microsatellite Instability Status.

In patients with colorectal cancer (CRC), the BRAF V600E mutation has been reported to be associated with several clinicopathological features and poor survival. However, the prognostic implications of BRAF V600E mutation and the associated clinicopathological characteristics in CRCs remain controversial. Therefore, we reviewed various clinicopathological features, including BRAF status, in 349 primary CRCs and analyzed the relationship between BRAF status and various clinicopathological factors, including overall survival. Similar to previous studies conducted in Eastern countries, the incidence of the BRAF V600E mutation in the current study was relatively low (5.7%). BRAF-mutated CRC exhibits distinct clinicopathological features from wild-type BRAF-expressing cancer independent of the microsatellite instability (MSI) status. This mutation was significantly associated with a proximal tumor location (P = 0.002); mucinous, signet ring cell, and serrated tumor components (P < 0.001, P = 0.003, and P = 0.008, respectively); lymphovascular invasion (P = 0.004); a peritumoral lymphoid reaction (P = 0.009); tumor budding (P = 0.046); and peritoneal seeding (P = 0.012). In conclusion, the incidence of the BRAF V600E mutation was relatively low in this study. BRAF-mutated CRCs exhibited some clinicopathological features which were also frequently observed in MSI-H CRCs, such as a proximal location; mucinous, signet ring cell, and serrated components; and marked peritumoral lymphoid reactions.

Abstract A006: Frameshift peptide neoantigens as vaccine targets in microsatellite-unstable cancers

Abstract Background: Deficient DNA mismatch repair (MMR) boosts the accumulation of frameshift mutations in genes encompassing coding microsatellites (cMS). This results in translation of proteins with mutation-induced frameshift peptide (FSP) neoantigens rendering MMR-deficient microsatellite-unstable (MSI) cancers highly immunogenic. Patients with MSI cancers and healthy individuals affected by Lynch syndrome, an inherited prediposition for MSI cancers, develop specific immune responses against these neoantigens. MSI cancers are unique in tumor immunology, because they express a defined set of long neoantigens that result from functionally relevant driver mutations and therefore are shared by the majority of MSI cancers. Consequently, MSI cancers in Lynch syndrome are an ideal model to evaluate the concept of cancer vaccines, which, with the increasing knowledge about mutational antigens in a wide variety of cancer types, can potentially be applied to many human cancer types. We here report the results of a clinical phase I/IIa trial as the first step to translate this concept into the clinical application. Methods: The vaccination protocol comprised 3 cycles of 4 subcutaneous applications of FSP antigens (frameshift variants of the coding microsatellite-containing genes AIM2, HT001, TAF1B) mixed with Montanide ISA-51 VG over a 6 month period. Inclusion criteria were history of MSI-H colorectal cancer (UICC stage III or IV) and completion of standard chemotherapy. Phase I of the trial evaluated safety and toxicity as the primary endpoint (6 patients), phase IIa addressed the induction of cellular and humoral immune responses (16 patients). Results: Significant induction of FSP-specific immune responses against one or more FSP antigens was observed in all patients vaccinated per protocol. No vaccination-induced systematic severe adverse events occurred. Few patients had stage IV disease and were evaluable according to RECIST. One heavily pretreated patient with bulky metastases showed a stable disease and stable CEA levels over 7 months under the study treatment. Conclusions: Vaccination with FSPs is well tolerated and leads to the induction of humoral and cellular immune responses. FSP vaccination represents a promising novel approach for treatment of MSI cancer patients and for tumor prevention in Lynch syndrome, allowing the evaluation of the concept of preventive cancer vaccines in an ideal model scenario of a defined high-risk patient population. Note: This abstract was not presented at the conference. Citation Format: Magnus von Knebel Doeberitz, Matthias Kloor, Miriam Reuschenbach, Claudia Pauligk, Mohammad-Reza Rafiyan, Salah-Eddin Al Batran, Julia Karbach, Mirjam Tariverdian, Elke Jaeger. Frameshift peptide neoantigens as vaccine targets in microsatellite-unstable cancers [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A006.

Abstract 2751: Frequent BRCA2 somatic mutations in colorectal cancer patients with microsatellite instability (MSI)

Abstract Microsatellite instability (MSI) is a hallmark of mismatch repair (MMR)-deficient cancers including colorectal cancer (CRC). MSI represents 15% of CRCs as a result of either epigenetic silencing of MLH1 or mutations in one of the MMR genes: MLH1, MSH2, MSH6 and PMS2. MSI tumors have a better prognosis than microsatellite stable (MSS) tumors while responding differently to treatments, including relative resistance to 5-FU and high clinical benefit from immune checkpoint therapy. Deficient MMR can lead to deficient DNA double-strand-break repair. We recently reported on 26 MSI-High and 558 non-MSI-High CRCs profiled by Caris Life Sciences. MSI-High CRCs had a high mutation rate (50%) in BRCA2 (Shagisultanova et al., 2015 ASCO Annual Meeting Abstract No. e14684 “Association of increase in BRCA2 gene mutations in microsatellite instable (MSI-H) colorectal cancer (CRC) with increased c-MET expression”). We hypothesized there might be a pattern with specific BRCA2 mutations in MSI-H CRCs targeting the coding microsatellites in BRCA2. BRCA2 mutations could be potential targets in clinical therapy. We further investigated functional mutation patterns in BRCA2 in both MSI-H and MSS groups. Of 1104 profiled CRCs in the COSMIC v73 database, somatic BRCA2 mutations were mapped for 101 MSI-High versus 916 MSS CRCs. MSI-High CRCs showed a significantly higher mutation rate in BRCA2 as compared to MSS (38% vs 6%, P&amp;lt;0.0000001). A higher rate of damaging mutations (42% vs. 2%, P&amp;lt; 0.0001) and a relatively distinct pattern of protein mutation distribution could be clearly mapped in MSI-High CRCs versus the MSS group. We found that specific mutations in coding microsatellites of BRCA2 can be impacted by MMR defects. We found 72 unique BRCA2 mutations in MSI-H CRCs not previously seen in either breast cancer or pancreatic cancer as reported in COSMIC v73. However, using the BIC database (http://research.nhgri.nih.gov/bic/) we detected 5 BRCA2 deleterious mutations that have been reported as germline mutations in breast cancer. We used the consensus result from five predictors and available 3-D structural information to predict deleterious properties of mutations including damaging BRCA2 protein structure and disruption of interactions with partner proteins including DSS1 and RAD51. Targeting BRCA2 mutations in MSI tumors and using the concept of synthetic lethality might be effective in BRCA-deficient CRCs with MSI. Citation Format: Safoora Deihimi, Avital Lev, Elena Shagisultanova, Joanne Xiu, Michael Slifker, Qifang Xu, David T. Dicker, Eric A. Ross, Roland Dunbrack, Wafik S. El-Deiry. Frequent BRCA2 somatic mutations in colorectal cancer patients with microsatellite instability (MSI). [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 2751.

Effects of microsatellite instability on recurrence patterns and outcomes in colorectal cancers.

Background:Among colorectal cancers (CRCs), high-frequency microsatellite instability (MSI-H) is associated with a better prognosis, compared with low-frequency MSI or microsatellite stability (MSI-L/MSS). However, it is unclear whether MSI affects the prognosis of recurrent CRCs.Methods:This study included 2940 patients with stage I–III CRC who underwent complete resection. The associations of MSI status with recurrence patterns, disease-free survival (DFS), overall survival from diagnosis to death (OS1), and overall survival from recurrence to death (OS2) were analysed.Results:A total of 261 patients (8.9%) had MSI-H CRC. Patients with MSI-H CRC had better DFS, compared to patients with MSI-L/MSS CRC (hazard ratio (HR): 0.619, P<0.001). High-frequency microsatellite instability CRC was associated with more frequent local recurrence (30.0% vs 12.0%, P=0.032) or peritoneal metastasis (40.0% vs 12.3%, P=0.003), and less frequent lung (10.0% vs 42.5%, P=0.004) or liver metastases (15.0% vs 44.7%, P=0.01). Recurrent MSI-H CRC was associated with worse OS1 (HR: 1.363, P=0.035) and OS2 (HR: 2.667, P<0.001). An analysis of patients with colon cancer yielded similar results.Conclusions:Recurrence patterns differed between MSI-H CRC and MSI-L/MSS CRC, and recurrent MSI-H CRCs had a worse prognosis.

Patterns of recurrence by microsatellite instability in colorectal cancer.

501 Background: Although colorectal cancer (CRC) with microsatellite instability (MSI) has a more favorable prognosis than microsatellite stable (MSS) CRC, patterns of recurrence has not been precisely investigated. We aim to explore patterns of recurrence and prognosis of CRC with MSI-H (high-frequency MSI) in comparison to MSI-L (low-frequency of MSI)/MSS. Methods: Patients with stage I-III colorectal cancer who received complete surgical resection were included using retrospective cohort of Yonsei Cancer Center. Patients were categorized to MSI status (MSI-H vs. MSS-L/MSS). Patterns of recurrence, disease free survival (DFS) and overall survival (time from diagnosis to death as OS1 and time from recurrence to death as OS2) between two groups were compared. Results: A total of 2944 patients were evaluated. Of all, 263 patients (8.9%) has MSI-H tumor. Patients with MSI-L/MSS tumor experienced more systemic recurrence events than patients with MSI-H tumor (13.1% vs. 4.6%). In patients who experienced recurrence, MSI-H tumor has tendency toward young age, proximal location and poorly differentiated histology. MSI-H tumor is more likely to recur as peritoneal metastasis (33.3% vs. 8.0%, p-value 0.002) and lymph node metastasis (25.0% vs. 7.7%, p-value 0.033). In contrast, MSI-L/MSS tumor is more likely to recur as lung metastasis (37.1% vs. 0.0%, p-value 0,008). There was no difference in DFS [hazard ratio (HR) = 0.753, p-value 0.241] and OS1 [HR = 1.486, p-value 0.203]. However, OS2 was marginally inferior in MSI-H tumor [HR = 1.779, p-value 0.064]. Conclusions: Patterns of recurrence in MSI-H CRC is different from that of MSI-L/MSS and modification of surveillance strategy in MSI-H CRC should be considered. In addition, prognosis of recurred MSI-H CRC is not superior than MSI-L/MSS and prognostic value of MSI in this circumstance should be evaluated using larger sample size.

Microsatellite instability & survival in patients with stage II/III colorectal carcinoma.

Background & objectives:The two key aspects associated with the microsatellite instability (MSI) as genetic phenomenon in colorectal cancer (CRC) are better survival prognosis, and the varying response to 5-fluorouracil (5-FU)-based chemotherapy. This study was undertaken to measure the survival of surgically treated patients with stages II and III CRC based on the MSI status, the postoperative 5-FU treatment as well as clinical and histological data.Methods:A total of 125 consecutive patients with stages II and III (American Joint Committee on Cancer, AJCC staging) primary CRCs, were followed prospectively for a median time of 31 months (January 2006 to December 2009). All patients were assessed, operated and clinically followed. Tumour samples were obtained for cytopathological verification and MSI grading.Results:Of the 125 patients, 21 (20%) had high MSI (MSI-H), and 101 patients (80%) had MSI-L or MSS (low frequency MSI or stable MSI). Patients with MSS CRC were more likely to have recurrent disease (P=0.03; OR=3.2; CI 95% 1-10.2) compared to those with MSI-H CRC. Multi- and univariate Cox regression analysis failed to show a difference between MSI-H and MSS groups with respect to disease-free, disease-specific and overall survival. However, the disease-free survival was significantly lower in patients with MSI-H CRC treated by adjuvant 5-FU therapy (P=0.03).Interpretation & conclusions:MSI-H CRCs had a lower recurrence rate, but the prognosis was worse following adjuvant 5-FU therapy.

Low density of FOXP3-positive T cells in normal colonic mucosa is related to the presence of beta2-microglobulin mutations in Lynch syndrome-associated colorectal cancer

ABSTRACTMicrosatellite instability (MSI-H) is caused by DNA mismatch repair deficiency and occurs in 15% of colorectal cancers. MSI-H cancers generate highly immunogenic frameshift peptide (FSP) antigens, which elicit pronounced local immune responses. A subset of MSI-H colorectal cancers develops in frame of Lynch syndrome, which represents an ideal human model for studying the concept of immunoediting. Immunoediting describes how continuous anti-tumoral immune surveillance of the host eventually leads to the selection of tumor cells that escape immune cell recognition and destruction. Between 30 and 40% of Lynch syndrome-associated colorectal cancers display loss of HLA class I antigen expression as a result of Beta2-microglobulin (B2M) mutations. Whether B2M mutations result from immunoediting has been unknown. To address this question, we related B2M mutation status of Lynch syndrome-associated colorectal cancer specimens (n = 30) to CD3-positive, CD8-positive and FOXP3-positive T cell infiltration in both tumor and normal mucosa. No significant correlation between B2M mutations and immune cell infiltration was observed in tumor tissue. However, FOXP3-positive T cell infiltration was significantly lower in normal mucosa adjacent to B2M-mutant (mt) compared to B2M-wild type (wt) tumors (mean: 0.98% FOXP3-positive area/region of interest (ROI) in B2M-wt vs. 0.52% FOXP3-positive area/ROI in B2M-mt, p = 0.023). Our results suggest that in the absence of immune-suppressive regulatory T cells (Treg), the outgrowth of less immunogenic B2M-mt tumor cells is favored. This finding supports the immunoediting concept in human solid cancer development and indicates a critical role of the immune milieu in normal colonic mucosa for the course of disease.