Microsatellite Instability Results Research Articles

Current laboratory testing practices for mismatch repair deficiency and microsatellite instability testing: A survey-based review of current laboratory practices.

To describe mismatch repair (MMR) and microsatellite instability (MSI) testing practices in laboratories using the College of American Pathologists (CAP) MSI/MMR proficiency testing programs prior to the 2022 publication of the MSI/MMR practice guidelines copublished by CAP and the Association of Molecular Pathology (AMP). Data from supplemental questionnaires provided with the 2020-B MSI/MMR programs to 542 laboratories across different practice settings were reviewed. Questionnaires contained 21 questions regarding the type of testing performed, specimen/tumor types used for testing, and clinical practices for checkpoint blockade therapy. Domestic laboratories test for MSI/MMR more often than international laboratories (P = .04) and academic hospitals/medical centers test more frequently than nonhospital sites/clinics (P = .03). The most commonly used testing modality is immunohistochemistry, followed by polymerase chain reaction, then next-generation sequencing. Most laboratories (72.6%; 347/478) reported awareness of the use of immune checkpoint inhibitor therapy for patients with high MSI or MMR-deficient results. The results demonstrate the state of MMR and MSI testing in laboratories prior to the publication of the CAP/AMP best practice guidelines, highlighting differences between various laboratory types. The findings indicate the importance of consensus guidelines and provide a baseline for comparison after their implementation.

Abstract A107: Characterizing the genomic and immunologic landscape of serous borderline tumors and low-grade serous ovarian cancer

Abstract A107: Characterizing the genomic and immunologic landscape of serous borderline tumors and low-grade serous ovarian cancer

128. Clinical testing of mismatch repair in neoplasms using multiple laboratory methods

<h3>Background</h3> Deficiency of DNA mismatch repair function can be assessed by immunohistochemical (IHC) analysis for loss of expression of the mismatch repair (MMR) proteins MLH1, MSH2, MSH6 and PMS2 or microsatellite instability (MSI) analysis. In some cases, however, there is a discrepancy between IHC and MSI analysis. Our aim was to explain with molecular mutation analysis these discordant cases between IHC and MSI results. <h3>Methods</h3> We reviewed 706 neoplasms accessioned between 2015-2021 (345 gastrointestinal, 142 genitourinary, 192 gynecologic, 27 miscellaneous). All neoplasms were assessed by IHC testing, MSI analysis and tumor-normal paired next generation sequencing (NGS) analysis, and 80% of cases with MLH1 loss had concurrent MLH1 methylation analysis. <h3>Results</h3> Fifty-eight (8.2%) of neoplasms had deficient MMR. Forty-four (76%) of these patients had both dMMR and MSI-high status. Ten of 14 discordant cases had a major discordance between IHC and MSI analysis: [MSI-High/intact MMR expression (n=3), microsatellite stable (MSS)/loss of MLH1&PMS2 (n=1), MSS/loss of MSH2&MSH6 (n=3), MSS/loss of MSH6 (n=3), MSS/loss of MSH1 &MSH2 (n=1)]. Remaining 4 neoplasms are either MSI-low or with equivocal IHC results. Methylation and NGS analysis revealed a molecular etiology in 3 of 10 (30%) neoplasms with major discordance, whereas in neoplasms without major discordance, this figure was 77%. (p=0.007) <h3>Conclusion</h3> For most neoplasms, IHC and MSI testing are concordant, and a molecular etiology that explains dMMR or MSI-High results can be identified. For neoplasms with major discordance, the addition and integration of NGS results and MLH1 methylation analysis can be beneficial for resolving borderline cases.

Microsatellite Instability Testing for Lynch Syndrome in Colorectal Adenomas

BackgroundPatients with Lynch Syndrome (LS), a hereditary condition linked to increased risk of colorectal cancer (CRC) and a variety of other cancers, carry at least one germline variant in a DNA mismatch repair protein (MMR) gene, which results in microsatellite instability (MSI). Screening for MMR/MSI status in CRCs helps identify patients with LS, which is imperative for treatment and surveillance. MSI high instability (MSI‐H) status has been detected in some colorectal adenomatous polyps (CRAs). If MSI‐H can be detected in CRAs from LS patients, this could aid in the prevention of cancer development and facilitate early surveillance. Currently, MMR/MSI testing in CRAs is not used to identify cases of LS. Here we analyze a set of CRAs to assess the utility of using MSI testing to identify patients with LS.DesignAfter completing a retrospective review of our pathology database, we selected 54 CRAs (including tubular, villous, and tubulovillous CRAs) from 32 patients with a history of LS, 21 CRAs from 14 patients with history of sporadic CRC with BRAF mutation or MLH1 promotor methylation, and 38 CRAs from 34 patients who underwent screening colonoscopy. Results from previous molecular testing confirmed germline mutations in the LS group and BRAF mutations or MLH1 promotor methylation in the sporadic CRC group. FFPE tissue was analyzed for MSI status using the Idylla MSI assay (Biocartis, Belgium). Patient demographics and clinical characteristics, pathologic features CRAs, and MSI results were analyzed.ResultsFrequency of MSI‐H CRA was significantly higher in the LS group (18.5%, [10/54]) than in the sporadic CRC (4.8%, [1/21]) and screening colonoscopy (0/38) groups. CRAs analyzed included 106 tubular CRAs, 2 villous CRAs and 5 tubulovillous CRAs. The MSI‐H CRAs in the LS group included 9 tubular CRAs and one villous CRA. One MSI‐H tubular CRA was identified in the sporadic CRC group. All CRAs from the screening colonoscopy group were MSI stable. Mean ages in years for patients in each study group were 56.9 in the LS group, 79.2 in the sporadic CRC group, and 60.6 in the screening colonoscopy group.ConclusionMSI‐H status is detectable in CRAs from patients with LS. MSI‐H CRAs are more frequently detected in patients with LS than non‐LS patients. These findings demonstrate the utility of MSI testing in CRAs. This can help to identify LS at a pre‐malignant stage, which prevents cancer development and facilitates early surveillance.

Association between microsatellite instability and tumor response to neoadjuvant chemoradiotherapy for rectal cancer

PurposeThe relationship between microsatellite instability (MSI) and tumor response after neoadjuvant chemoradiotherapy (nCRT) in rectal cancer remains unclear. The present study aimed to evaluate the association between MSI and tumor response to nCRT in rectal cancer treatment.MethodsPatients with rectal cancer from 2 tertiary hospitals who underwent nCRT, followed by radical surgery, were included. The microsatellite status was determined using a PCR-based Bethesda panel. Tumors with a Dworak’s tumor regression grade of 3 or 4 were considered to have a good response. Predictive factors for a good response to nCRT were analyzed.ResultsOf the 1,401 patients included, 910 (65.0%) had MSI results and 1.5% (14 of 910) showed MSI-H. Among all the patients, 519 (37.0%) showed a good response to nCRT. A univariate analysis showed that MSI-H tended to be negatively associated with a good response to nCRT, but no statistical significance was observed (7.1% vs. 24.1%, P = 0.208). Multivariate analysis showed that well-differentiated tumors were the only predictive factor for good response to nCRT (odds ratio [OR], 2.241; 95% confidence interval [CI], 1.492–3.364; P < 0.001). MSI status tended to be associated with the response to nCRT (OR, 0.215; 95% CI, 0.027–1.681; P = 0.143).ConclusionMSI-H was not associated with response to nCRT in patients with rectal cancer.

Investigation of discrepant mismatch repair immunohistochemistry and microsatellite instability polymerase chain reaction test results for gynecologic cancers using next-generation sequencing

Gynecologic cancers are routinely screened for DNA mismatch repair (MMR) gene mutations using immunohistochemistry (IHC) and/or polymerase chain reaction (PCR) for microsatellite instability (MSI) to enable selection of immune checkpoint inhibitor therapy and screen for Lynch syndrome. The limited data that compareIHC and MSI in endometrial tumors have shown discordance rates of 5-10%. We reviewed MMR/MSI results in gynecologic cancers and used next-generation sequencing (NGS) to interrogate discrepancies. Of the 328 cases with both IHC and MSI results, 256 (78.0%) were microsatellite stable (MSS) with preserved MMR (pMMR), 64 (19.5%) cases were MSI-High (MSI-H) with MMR deficient (dMMR), 2 cases showed subclonal loss of MLH1 and PMS2 with MSI-H, and 6 cases were discordant. Overall, there was a 98.2% (322/328) IHC/MSI concordance. Discordant cases were retested and/or subject to NGS. Of the six discrepant cases, five showed dMMR with MSS and one showed pMMR with MSI-H. One dMMR/MSI-L case showed loss of PMS2 with a germline pathogenic mutation. The pMMR/MSI-H case was found to harbor pathogenic variants in MLH1 and MSH6. One of the two cases with subclonal populations demonstrated MSI-H in the dMMR area and MSS in the pMMR area. These results emphasize the importance of selecting the appropriate tumor tissue for both IHC and molecular testing and demonstrate that NGS can help resolve discrepant MMR and MSI results.

Frequency of microsatellite instability (MSI) in upper tract urothelial carcinoma: comparison of the Bethesda panel and the Idylla MSI assay in a consecutively collected, multi-institutional cohort

AimsUpper tract urothelial carcinoma (UTUC) is a rare malignancy with a poor prognosis which occurs sporadically or in few cases results from a genetic disorder called Lynch syndrome. Recently, examination...

Mismatch repair protein expression of colorectal cancer: a retrospective analysis of 3 428 cases

Objective: To analyze the expression of mismatch repair (MMR) proteins in colorectal cancers (CRC) and to evaluate the feasibility and potential pitfalls of immunohistochemistry (IHC) analysis for MMR. Methods: The IHC sections for MMR proteins were reviewed in 3 428 cases of resected CRC without neoadjuvant therapy at Tianjin Medical University Cancer Institute and Hospital from July 2014 to October 2018. For the cases with unclear MMR IHC results during the initial review, IHC staining was repeated and microsatellite instability (MSI) analysis was performed. Relationships between the expression of MMR proteins and MSI status as well as the clinicopathological parameters were analyzed. Results: IHC staining for MMR was repeated in 28 (0.8%) cases due to poor quality of original IHC sections. Inconsistent results between the original diagnosis and re-diagnosis were found in 119 (3.5%) cases, mainly resulting from PMS2 and MLH1. Finally, 261 (7.6%) cases of CRC showed mismatch repair deficiency (dMMR), mainly from the deficiency of both MLH1 and PMS2 (43.3%,113/261). In the 14 cases with MSI results, the concordant of MSI and MMR was 13 cases. In the 29 dMMR cases with next generation sequencing (NGS) results, the concordant of MSI-high and dMMR was 93.1%(27/29). The cases with inconsistent results between MSI and MMR showed negative expression of MSH6 or PMS2. Twenty-one CRC showed negative expression of MLH1 and partially positive (or weak positive) expression of PMS2, or negative expression of MSH2 and partially positive (or weak positive) expression of MSH6. Among the 19 cases with MSI results, 16 cases were MSI-high, two cases were MSI-low, and one case was microsatellite stable. Compared with mismatch repair proficiency (pMMR), dMMR was more frequently detected in female patients younger than 50 years old, with family history, at early stage (Ⅰ-Ⅱ) CRC, and in the tumors from right colon,with poor differentiation, or mucinous adenocarcinoma/signet ring cell carcinoma (all P<0.05). Conclusions: At present, IHC staining is a clinically effective and convenient method to detect MMR expression, but the operating process and result assessment remain variable and need to be standardized. MSI analysis can be performed in the difficult-to-evaluate cases for MMR to enhance prognostic evaluation and treatment option.

Immunohistochemical Expression Pattern of MLH1, MSH2, MSH6, and PMS2 in Tumor Specimen of Iranian Gastric Carcinoma Patients

Gastric cancer is the third leading cause of cancer-related death. Determining molecular and histopathologic tumor features, which may contribute to the development or progression of gastric cancer, can improve the prognosis. Expression patterns of DNA repair proteins such as MLH1, MSH2, MSH6, and PMS2 that are associated with microsatellite instability (MSI) are some of the markers that are useful in predicting the prognosis of gastric cancer. The purpose was to determine the immunohistochemical expression pattern of MLH1, MSH2, MSH6, and PMS2 in tumor specimens of Iranian gastric carcinoma patients. In this prospective cohort, 186 consecutive patients with gastric cancer, attending Taleghani Hospital, were enrolled. The immunohistochemical expression patterns of MLH1, MSH2, MSH6, and PMS2 in tumor specimens among them were determined. The results of this study demonstrated that 91.4% of our gastric cancer patients were negative for MSI, and 8.6% of them were MSI positive. The positive MSI was seen in 5.9% and 15.7% of male and female subjects, respectively, with a significant difference (P = 0.043). The other variables were not related to MSI results (P > 0.05). According to the obtained results, the expression of MLH1, MSH2, MSH6, and PMS2 in tumor specimens is positive in 8.6% of the total Iranian gastric cancer sample size, which is mainly positive in female subjects. However, it is not related to the location and stage of the tumor.

Identifying mismatch repair-deficient colon cancer: near-perfect concordance between immunohistochemistry and microsatellite instability testing in a large, population-based series.

Establishing the mismatch repair (MMR) status of colorectal cancers is important to enable the detection of underlying Lynch syndrome and inform prognosis and therapy. Current testing typically involves either polymerase chain reaction (PCR)-based microsatellite instability (MSI) testing or MMR protein immunohistochemistry (IHC). The aim of this study was to compare these two approaches in a large, population-based cohort of stage 2 and 3 colon cancer cases in Northern Ireland. The study used the Promega pentaplex assay to determine MSI status and a four-antibody MMR IHC panel. IHC was applied to tumour tissue microarrays with triplicate tumour sampling, and assessed manually. Of 593 cases with available MSI and MMR IHC results, 136 (22.9%) were MSI-high (MSI-H) and 135 (22.8%) showed abnormal MMR IHC. Concordance was extremely high, with 97.1% of MSI-H cases showing abnormal MMR IHC, and 97.8% of cases with abnormal IHC showing MSI-H status. Under-representation of tumour epithelial cells in samples from heavily inflamed tumours resulted in misclassification of several cases with abnormal MMR IHC as microsatellite-stable. MMR IHC revealed rare cases with unusual patterns of MMR protein expression, unusual combinations of expression loss, or secondary clonal loss of expression, as further illustrated by repeat immunostaining on whole tissue sections. MSI PCR testing and MMR IHC can be considered to be equally proficient tests for establishing MMR/MSI status, when there is awareness of the potential pitfalls of either method. The choice of methodology may depend on available services and expertise.

Lynch syndrome identification in a Brazilian cohort of endometrial cancer screened by a universal approach

ObjectiveTo report the frequency of Lynch syndrome (LS) in a cohort of patients from Southeast Brazil bearing endometrial cancer (EC), using a tumor screening universal approach. MethodsA total of 242 endometrial carcinomas were screened by immunohistochemistry (IHC) and microsatellite instability (MSI) for detection of DNA mismatch repair deficiency (dMMR). MLH1 methylation was assessed to identify sporadic cases. Patients with dMMR tumors were recruited for germline variant analysis by next-generation sequencing of the MLH1, MSH2, MSH6, PMS2, and EPCAM genes. ResultsNinety-three out of 242 tumors (38.5%) were classified as dMMR based on MSI and IHC results. Of these, 54 cases were selected for germline analysis, and 37/54 (68.5%) were available for sequencing. Ten patients (10/37, 27%) harbored germline pathogenic or likely pathogenic variants, most of them in the MSH6 gene (4/10, 40%). Seven variants of uncertain significance were found. Eight novel germline variants were identified. The LS prevalence in our cohort was of at least 4.1%. LS patients presented lower mean age at cancer diagnosis compared with patients diagnosed with sporadic EC. Individuals with dMMR tumors, without germline pathogenic variants detected in LS-genes (“Lynch-like” syndrome), had an intermediate mean age at cancer diagnosis between LS and sporadic cases. ConclusionThis is the first report of the LS prevalence in EC screened by a universal approach in Brazil. Our findings contribute to a better understanding of the mutational landscape of this syndrome in Brazil, which is relevant for improved identification, genetic counseling, prevention and control of cancer in LS.

Abstract 1368: Simultaneous cell-free RNA PD-L1 expression and MSI from the same single-tube of blood in solid tumors

Abstract Background: Liquid biopsy is a minimally invasive technique available in the clinic using next-generation sequencing (NGS) of plasma circulating cell-free DNA (cfDNA) and cfRNA. Here we report liquid biopsy results from solid tumors using the Circulogene Theranostics Personalized Gene Profile (CGP, 50-gene panel), as well as, microsatellite instability (MSI) testing. CGP uses proprietary in situ enrichment requiring minimal input volume of 20 uL plasma (cfDNA), 400 uL (cfRNA), and 100 uL buffy coat per case from the same single-tube of blood. Methods: cfRNA PD-L1 expression, MSI, and co-occurring cfDNA mutations were retrospectively compiled from CGP ordered at multiple centers. Ct value cutoff for 1 copy PD-L1 (positive) was 42. MSI was performed using paired buffy coat gDNA (normal) and plasma cfDNA (tumor) on 5 microsatellite mononucleotide markers, BAT-25, BAT-26, NR-21, NR-24 and MONO-27 (Promega; current an industry standard that has been used in KEYNOTE pembrolizumab trials) and analyzed by capillary electrophoresis genetic analyzer. Based on batched processing, Circulogene’s turnaround time (TAT) is 5 business days on average. Data was summarized and the correlation between PD-L1 and MSI was measured. Results: 397 patients (median age 67 years, range 27-96; 210 men: 187 women) underwent CGP testing for both PD-L1 and MSI (11/2017-10/2018). The majority of cancer types were lung (n=187), colorectal (n=43), breast (n=40), pancreatic (n=32), and prostate (n=30). 59/397 (14.9%) were PD-L1 positive, in the range of expected PD-L1 positivity across solid tumors. 110/397 (27.7%) were MSI-High (MSI-H). There was no correlation between PD-L1 and MSI results (r^2 &amp;lt;0.01). There was a median of 3 mutations/patient (range 0-19), with a 0% sample failure rate. Overall, 23 cases had no detectable mutations (5.8%), but 11 of these 23 (47.8%) had either PD-L1 positivity or MSI-H. Conclusions: Simultaneous cfRNA PD-L1 and MSI testing from the same single-tube blood is feasible in a liquid biopsy and their positivity has frequency in the expected range for solid tumors (Xang et al. Onco Targets Ther 2016, Zhang et al. AMP Conference 2018, Abstract ST009). Despite the low plasma sample input, there were no sample failures, suggesting CGP in situ enrichment is robust and has a rapid TAT. Assay results with linkage to clinical outcomes is warranted. Citation Format: Glen J. Weiss, Paul Walker, Dilek Aktas, Andrew Ford, Charmaine Brown, Chen-Hsiung Yeh, Nader Javadi. Simultaneous cell-free RNA PD-L1 expression and MSI from the same single-tube of blood in solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1368.

Development and correlative analysis of a TML assay in specimens with reference MSI and somatic variant results.

124 Background: Treatment of late-stage non-small cell lung cancer has been greatly impacted by the advances in immunotherapy. Molecular biomarkers such as tumor mutation load (TML or TMB) and micro-satellite instability (MSI) may identify patients with NSCLC that are more likely to respond to immune checkpoint inhibitors. In this report, we describe the development of and NGS-based assay for the robust detection of TML and somatic variants simultaneously using a targeted assay that covers 1.7 Mb of the genome. Methods: Initial feasibility included reference control cell-lines, HCC1143 and NIST8398, as well as FFPE (formalin-fixed, paraffin-embedded) samples from lung and colorectal tumors. In development, eight FFPE specimens from patients with late stage cancer and a reference MSI status were evaluated. FFPE slides were extracted using the MagMax FFPE DNA/RNA Ultra kit, and nucleic acid quality was assessed using qPCR. Extracted DNA was processed through the Oncomine TML Assay with a minimum input of 30 ng of DNA per specimen. Automated library and template preparation were performed followed by sequencing on the Ion GeneStudio S5 Plus system using replicate 540 chips. Eight samples with barcoded adapters were multiplexed per chip. Tumor mutation analysis and variant calling was performed using the Oncomine TML v2.0 workflow. Results: The time from FFPE extraction to result was 96 hours, and all samples passed QC metrics. TML scores ranged from 14.4-36.04 mutations/Mb for all samples with MSI-high reference results. A very high level of inter-chip concordance was also observed (R2=0.990). Additionally, the variant caller function within the TML workflow was used to detect BRAF V600E mutations with 100% concordance to reference testing results. Conclusions: The accurate quantification of somatic mutations paired with fast turn-around time and robust automated workflow is ideal for assessing the tumor mutation load as well as hotspot mutations from limited (FFPE) samples.

Prognostic Value of the Microsatellite Instability Status in Patients With Stage II/III Rectal Cancer Following Upfront Surgery

BackgroundWe investigated whether the microsatellite instability (MSI) status affects the survival outcomes in patients with stage II/III rectal cancer who have undergone an upfront curative resection. Patients and MethodsA total of 1103 patients with curatively resected stage II/III rectal cancer who had available polymerase chain reaction-based MSI results were included in the final analysis. ResultsTwenty-four (2.2%) patients in the total cohort were found to be MSI-high (MSI-H). In univariate analysis, neither disease-free survival (DFS) nor overall survival (OS) demonstrated significant differences between patients with MSI-H tumors and those with MSI-low (MSI-L) or microsatellite stable (MSS) tumors. The 5-year DFS rate was 78.0% in MSI-H patients and 69.9% in MSI-L/MSS patients (hazard ratio [HR], 0.84; 95% confidence interval [CI], 0.35-2.02; P = .689). The 5-year OS rates for MSI-H and MSI-L/MSS patients were 84.0% and 83.1%, respectively (HR, 0.86; 95% CI, 0.27-2.69; P = .790). By multivariate analysis, the MSI status did not affect either the DFS (HR, 1.00; 95% CI, 0.40-2.47; P = .994) or OS (HR, 0.85; 95% CI, 0.26-2.73; P = .778). ConclusionsMSI-H tumors are rarely observed in rectal adenocarcinoma, and the MSI status may not affect the survival outcome in patients with a resected rectal cancer.

Abstract PD6-03: Distribution of microsatellite instability, tumor mutational load, and PD-L1 status in molecularly profiled invasive breast cancer

Abstract Background: Recent data indicate a promising response to immune check point blockade (ICB) in patients with breast cancer. Pembrolizumab, a humanized monoclonal antibody against programmed death 1 (PD-1) receptor and one of several ICB agents in development, was given an FDA approval for all MSI (microsatellite instability)-high solid tumors. MSI incidence in breast cancer is not fully elucidated. Other biomarkers being explored in possible relationship to ICB activity include PD-1 ligand (PD-L1) status and tumor mutational load (TML). In this study, we aimed to explore the incidence of these biomarkers in invasive breast cancers. Methods: A retrospective data analysis of patients profiled by commercial next-generation sequencing (NGS) at Caris Life Sciences was performed. MSI results were either high, stable, or equivocal. MSI was calculated by comparing repeat-insertions or deletions across over 7,000 microsatellite sequences in the patient sample to the hg19 reference genome. Samples with repeat variances in more than 45 microsatellites were classified as MSI-High PD-L1 expression was evaluated using immunohistochemical analysis (IHC), with clone SP-142 (Roche Diagnostics). A sample was considered positive if there was &amp;gt;5% membranous staining of tumor cells. Tumor mutational load was calculated as a total number of non-synonymous somatic mutations identified per megabase of the genome coding area with high being greater than or equal to 17. Results: A total of 9,627 breast cancer cases were queried from the Caris Life Sciences database. The mean age (±SD) was 56.8 ± 12.4 years (range 20-90). The tumor distribution was 60.7% hormone receptor (HR) positive (ER and/or PR) and HER2 negative, 9.5% HER2 positive (with HR negative or positive), and 29.8% triple negative (negative for ER, PR and HER2). Of all cases, there were 5,203 tested for PD-L1 status, 354 (6.8%, 95% CI 6.2-7.5%) were positive. Of 1,440 tumors tested for MSI status, 15 (1.04%, 95% CI 0.58-1.71%) were either high (8) or equivocal (7), the rest were MSI-low. Tumor mutational load (TML) was available on 1,766 tumors, of which 55 (3.1%, 95% CI 2.4-4.0%) were high. Seven out of the 8 MSI-high tumors were also TML-high. Four out of the 8 MSI-high breast cancers were triple negative. Conclusion: In this large dataset of molecularly profiled breast cancer, MSI was observed in about 1% of the breast tumors tested. Overall, modest positivity of TML, PD-L1, and MSI of all invasive breast cancers was observed. The percentage of patients that had at least one of these biomarkers that may confer responsiveness to ICB is planned and will be further stratified by subtype. MSI-high breast cancers mostly overlapped with those that were TML-high. Future research is needed to show the clinical utility of these biomarkers in response to ICB. Updated data will be presented. Citation Format: Obeid E, Ellerbrock A, Handorf E, Goldstein L, Gatalica Z, Arguello D, Swain SM, Isaacs C, Vacirca J, Tan A, Schwartzberg L. Distribution of microsatellite instability, tumor mutational load, and PD-L1 status in molecularly profiled invasive breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD6-03.

Mismatch Repair Deficiency, Microsatellite Instability, and Survival

Mismatch repair (MMR) deficiency (MMRD) and microsatellite instability (MSI) are prognostic for survival in many cancers and for resistance to fluoropyrimidines in early colon cancer. However, the effect of MMRD and MSI in curatively resected gastric cancer treated with perioperative chemotherapy is unknown. To examine the association among MMRD, MSI, and survival in patients with resectable gastroesophageal cancer randomized to surgery alone or perioperative epirubicin, cisplatin, and fluorouracil chemotherapy in the Medical Research Council Adjuvant Gastric Infusional Chemotherapy (MAGIC) trial. This secondary post hoc analysis of the MAGIC trial included participants who were treated with surgery alone or perioperative chemotherapy plus surgery for operable gastroesophageal cancer from July 1, 1994, through April 30, 2002. Tumor sections were assessed for expression of the MMR proteins mutL homologue 1, mutS homologue 2, mutS homologue 6, and PMS1 homologue 2. The association among MSI, MMRD, and survival was assessed. Interaction between MMRD and MSI status and overall survival (OS). Of the 503 study participants, MSI results were available for 303 patients (283 with microsatellite stability or low MSI [median age, 62 years; 219 males (77.4%)] and 20 with high MSI [median age, 66 years; 14 males (70.0%)]). A total of 254 patients had MSI and MMR results available. Patients treated with surgery alone who had high MSI or MMRD had a median OS that was not reached (95% CI, 11.5 months to not reached) compared with a median OS among those who had neither high MSI nor MMRD of 20.5 months (95% CI, 16.7-27.8 months; hazard ratio, 0.42; 95% CI, 0.15-1.15; P = .09). In contrast, patients treated with chemotherapy plus surgery who had either high MSI or MMRD had a median OS of 9.6 months (95% CI, 0.1-22.5 months) compared with a median OS among those who were neither high MSI nor MMRD of 19.5 months (95% CI, 15.4-35.2 months; hazard ratio, 2.18; 95% CI, 1.08-4.42; P = .03). In the MAGIC trial, MMRD and high MSI were associated with a positive prognostic effect in patients treated with surgery alone and a differentially negative prognostic effect in patients treated with chemotherapy. If independently validated, MSI or MMRD determined by preoperative biopsies could be used to select patients for perioperative chemotherapy.

Clinical significance of fibroblast growth factor receptor 2 expression in patients with residual rectal cancer after preoperative chemoradiotherapy: relationship with KRAS or BRAF mutations and MSI status.

This study was designed to determine the prognostic impact and clinical significance of FGFR2 in residual disease after preoperative chemoradiotherapy (CRT) in patients with rectal cancer. The surgical specimens of 145 patients with residual rectal cancer after preoperative CRT were analyzed. To evaluate FGFR2 expression, immunohistochemistry was performed on whole section tissues. KRAS exon 2 (codon 12 and 13), BRAF V600E mutational status, and microsatellite instability (MSI) were determined using polymerase chain reactions. Of the eligible 141 patients, FGFR2 over-expression was observed in 75.9% (n = 107) and was correlated with perineural invasion (P = 0.005) and inferior tumor regression grading (TRG) (P = 0.009). However, FGFR2 expression had no relationship with KRAS and BRAF mutation results or with MSI results. On univariate analysis, FGFR2 over-expression was significantly associated with worse rectal cancer-specific survival (RCSS) (P = 0.005) and disease-free survival (DFS) (P = 0.035). However, multivariate analysis revealed that FGFR2 over-expression was not independently associated with RCSS and DFS (all P > 0.05). Although FGFR2 over-expression did not independently influence patient outcome, FGFR2 over-expression was associated with worse prognosis and inferior TRG. Our data may aid in understanding the therapeutic approaches targeting FGFR2 in patients with residual rectal cancer after preoperative CRT.

Determinants of Colectomy in Young Colorectal Cancer Patients Age ≤50: A Statewide, Populationbased Study

Introduction: Hereditary colorectal cancer (CRC), including Lynch Syndrome (LS) and polyposis syndromes, and Inflammatory Bowel Disease (IBD) may underlie CRC development in approximately 25% of young patients. Colectomy is recommended in these high-risk cases, and considered in young patients in general, as more limited resection may lead to metachronous CRC. As there are no population-based studies examining operative practices in young patients, we analyzed statewide Louisiana Tumor Registry (LTR) data to quantitate colectomy rates in those age ≤50 and assess predictors of more extensive surgery. Methods: Utilizing LTR data supplemented with data from a Centers for Disease Control and Preventionfunded Comparative Effectiveness Research project, we analyzed all patients ≤50 diagnosed with CRC in Louisiana in 2011 (surgical care extending into 2012). Operative type predictors evaluated included socio-demographics, tumor characteristics and healthcare facility type where surgery took place. Results: Of 2427 all-age, statewide CRC patients, 274 were ≤50. 234 underwent surgery at 53 unique facilities (table 1-baseline characteristics, age stratified). 6.8% (16/234) underwent colectomy. Colectomy predictors (table 2) included age ≤45, polyposis (>10 adenomas) (p < .0001), synchronous/metachronous LS-associated cancer (p < .0001) and IBD (p < .0241). Abnormal microsatellite instability (MSI), gender, race, health insurance status and healthcare facility type were not associated with colectomy. Conclusion: The low colectomy rate of 6.8% (ideally ≥25% based on historical hereditary CRC and IBD estimates in young patients) indicates a substantial number of those undergoing limited resection may be at risk for metachronous CRC. Obvious high-risk features including polyposis, IBD or synchronous/metachronous LS-associated cancers drive colectomy performance. Patients with abnormal MSI (LS risk) rarely undergo colectomy. We previously demonstrated a low MSI testing rate of 23% in this 2011 statewide CRC cohort and that MSI results were available pre-operatively in only 16.9% of cases (Karlitz et al, ACG meeting 2014 and Am J Gastroenterol. 2015 Jan 20. doi: 10.1038). These may be contributing factors to the low colectomy rate as failure to identify patients at risk for LS preoperatively and overall will prevent germline genetic testing, which can aid in surgical management decisions regarding resection extent. Young patients with presumed sporadic CRC do not undergo colectomy.Table 1: Descriptive Characteristics of Louisiana Residents Age ≤50 Diagnosed with Colorectal Cancer in 2011, Stratified by Age

Prognostic and predictive effect of microsatellite instability (MSI) in MAGIC.

62 Background: MSI is prognostic for survival in diverse cancers and predicts resistance to fluoropyrimidine chemotherapy in colon cancer. We examined the interaction between MSI and patient (pt) characteristics and survival for pts randomised to surgery alone or perioperative ECF chemotherapy in the MRC MAGIC trial. Methods: Tumor and normal control DNA was extracted from resection FFPE. MSI status was determined using the Promega MSI Analysis System (NR-21, BAT-26, BAT-25, NR-24, MONO-27). Tumors were classified as MSS when all markers were stable, MSI-L when only one marker was unstable and MSI-H with minimum of instability in two markers. MSI status was correlated with pt characteristics and survival. Results: MSI results were available for 303 pts (66% resected pts). Twenty (6.6%) and 2 (0.6%) pts were MSI-H and MSI-L. All pts with MSI-H had stomach tumors (vs.GEJ/esophagus). KRAS mutation was more common in MSI-H tumours (30% vs. 4%, p-value &lt;0.001); rates of BRAF, PIK3CA and TP53 mutations were comparable. Median overall survival (OS) from surgery was greater for pts with MSI-H tumours treated with surgery alone (1.69y for MSS vs. not reached for MSI-H) (Table 1), whereas patients with MSI-H tumors treated with chemotherapy plus surgery had inferior outcomes compared to MSS stable pts (median OS 0.8y vs. 1.89y respectively). An interaction test for MSI-H vs. MSS status and treatment arm was positive (p=0.007). Conclusions: In MAGIC, MSI-H status is associated with a positive prognostic effect in pts treated with surgery alone, and a negative predictive effect in pts treated with chemotherapy. As pt selection biomarkers for perioperative chemotherapy are lacking, validation of this finding in an independent dataset is warranted. [Table: see text]

Prevalence of Lynch Syndrome among Patients with Newly Diagnosed Endometrial Cancers

BackgroundLynch syndrome (LS) is a hereditary condition that increases the risk for endometrial and other cancers. The identification of endometrial cancer (EC) patients with LS has the potential to influence life-saving interventions. We aimed to study the prevalence of LS among EC patients in our population.MethodsUniversal screening for LS was applied for a consecutive series EC. Tumor testing using microsatellite instability (MSI), immunohistochemistry (IHC) for mismatch-repair (MMR) protein expression and MLH1-methylation analysis, when required, was used to select LS-suspicious cases. Sequencing of corresponding MMR genes was performed.ResultsOne hundred and seventy-three EC (average age, 63 years) were screened. Sixty-one patients (35%) had abnormal IHC or MSI results. After MLH1 methylation analysis, 27 cases were considered suspicious of LS. From these, 22 were contacted and referred for genetic counseling. Nineteen pursued genetic testing and eight were diagnosed of LS. Mutations were more frequent in younger patients (<50 yrs). Three cases had either intact IHC or MSS and reinforce the need of implement the EC screening with both techniques.ConclusionThe prevalence of LS among EC patients was 4.6% (8/173); with a predictive frequency of 6.6% in the Spanish population. Universal screening of EC for LS is recommended.