MSI-high Patients Research Articles

Abstract 5296: Instability of non standard microsatellites in metastatic colorectal cancer patients treated with a bevacizumab based chemotherapy

Abstract Bevacizumab (B) is a biological agent frequently included in the treatment of metastatic colon cancer (mCRC), although at present there is no effective biomarker that can predict its efficacy. Few studies report a positive association of microsatellite instability (MSI) with the response to anti-angiogenic therapy, but the role of MSI in relation to B efficacy needs to be better understood. Elevated microsatellite alterations at selected tetranucleotides repeats (EMAST) can be observed at higher rate in mCRC patients compared to MSI. The predictive and prognostic role of EMAST has not been completely investigated so far. Moreover, it is known that angiogenesis in mCRC goes through the activation of VEGF-A, but VEGF-B can be involved in some compensatory effect during anti-VEGF-A treatments. By exploring the UCSC Genome Browser database, we found that the VEGF-B gene possesses a poly-dinucleotide microsatellite (normally 19xAG) which somatic instability has never been reported. In this study, we analyzed the status of MSI, five EMAST markers (D20S82, D20S85, D8S321, D9S242, MYCL1) and the VEGF-B microsatellite in relation to prognosis in 145 mCRC patients treated with chemotherapy alone (n=51) or chemotherapy plus B (n=94). MSI high (MSI-H) was detected in four patients (3%) out of 141 participants. Using a multivariable model and adjusting for patient characteristics, microsatellite status remains significantly associated with progression free survival (PFS) and overall survival (OS). The PFS hazard ratio (HR) for MSI-H patients was 3.18 (95% CI 1.09-9.25; p=0.034) and the OS HR was 6.45 (95% CI 2.08-19.99; p=0.001). Eleven (7.8%) patients out of 140 were positive to at least two EMAST markers. EMAST instability was associated with a general worse prognosis, trend that become significant in the group of patients treated with CT plus B in term of PFS (median survival 5 months vs 11. months, p=0.0006) and OS (median survival 6.1 months vs 29.1 months, p<0.0001). The interaction test showed a significant association of D20S82 (PFS p=0.004) and MYCL1(PFS p=0.029), with worse prognosis when treated with CT plus B, adding a possible predictive value in mCRC patients. The 24.2% of patients (29 out of 120) showed a VEGF-B-poly-AG instability. Amplification of the poly-AG is associated with worse outcome in PSF (7.0 month of median survival vs 28.0 months for patients with shortened poly-AG; p=0.005) in patients treated with CT alone, suggesting that an extended microsatellite in VEGF-B might have a role in the resistance to chemotherapy. In conclusion, MSI, EMAST and VEGF-B poly-AG instability are associated with prognosis in mCRC patients treated with CT or CT plus B. MSI and EMAST instability are associated with worse prognosis in CT+B patients, while VEGF-B microsatellite instability is linked to worse prognosis in CT patients. Further investigations are needed but we can hypothesize that MSI, EMAST and VEGF-B poly-AG instability can have some relevance for the clinical outcome of the disease. Citation Format: Francesca Pirini, Luigi Pasini, Sara Ravaioli, Gianluca Tedaldi, Emanuela Scarpi, Giorgia Marisi, Chiara Molinari, Daniele Calistri, Alessandro Passardi, Paola Ulivi. Instability of non standard microsatellites in metastatic colorectal cancer patients treated with a bevacizumab based chemotherapy [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 5296.

Adjuvant Chemotherapy in Microsatellite Instability-High Gastric Cancer.

PurposeMicrosatellite instability (MSI) status may affect the efficacy of adjuvant chemotherapy in gastric cancer. In this study, the clinical characteristics of MSI-high (MSI-H) gastric cancer and the predictive value of MSI-H for adjuvant chemotherapy in large cohorts of gastric cancer patients were evaluated.Material and MethodsThis study consisted of two cohorts. Cohort 1 included gastric cancer patients who received curative resection with pathologic stage IB-IIIC. Cohort 2 included patients with MSI-H gastric cancer who received curative resection with pathologic stage II/III. MSI was examined using two mononucleotide markers and three dinucleotide markers.ResultsOf 359 patients (cohort 1), 41 patients (11.4%) had MSI-H. MSI-H tumors were more frequently identified in older patients (p < 0.001), other histology than poorly cohesive, signet ring cell type (p=0.005), intestinal type (p=0.028), lower third tumor location (p=0.005), and absent perineural invasion (p=0.027). MSI-H status has a tendency of better disease-free survival (DFS) and overall survival (OS) in multivariable analyses (hazard ratio [HR], 0.4; p=0.059 and HR, 0.4; p=0.063, respectively). In the analysis of 162 MSI-H patients (cohort 2), adjuvant chemotherapy showed a significant benefit with respect to longer DFS and OS (p=0.047 and p=0.043, respectively). In multivariable analysis, adjuvant chemotherapy improved DFS (HR, 0.4; p=0.040).ConclusionMSI-H gastric cancer had distinct clinicopathologic findings. Even in MSI-H gastric cancer of retrospective cohort, adjuvant chemotherapy could show a survival benefit, which was in contrast to previous prospective studies and should be investigated in a further prospective trial.

An Emerging Landscape for Canonical and Actionable Molecular Alterations in Primary and Metastatic Prostate Cancer.

Patients with prostate cancer with tumors harboring defects in DNA-repair genes (DRD) generally do not respond well to AR-directed therapy. Furthermore, canonical pathways evolve during disease progression and may affect treatment with existing therapies. Due to the limited treatment options after failure of hormonal and taxane therapy, and the tumor heterogeneity induced by DRD, we sought to characterize the alterations in primary and metastatic prostate cancer. Tumors from 1,027 patients with advanced prostate cancer that underwent comprehensive genomic profiling for routine clinical care were reviewed to assess DRD mutation rates (27-gene panel) and co-occurring mutations in select canonical prostate cancer pathways. DRD alterations were identified in 20 genes and in 17% of patients (BRCA2 and ATM most common) occurring with slightly higher frequency in specimens from metastatic biopsy sites and men older than 50 years of age. Microsatellite instability-high (MSI-H) and tumor mutational burden-high occurred with 3% frequency in the overall cohort but were not enriched in metastatic disease. Biomarkers previously associated with antitumor immunity are found at high frequencies in MSI-H patients, including JAK1 (68%) and PTEN (32%). Lastly, mutations in TP53, AR, PTEN, APC, CTNNB1, and PIK3CA were all significantly enriched in metastatic samples. We identified clinically significant subgroups of patients demonstrating (1) defects in DNA-repair pathways, (2) intrinsic prostate cancer signaling pathways that may prevent antitumor immunity, and (3) distinct genomic differences between localized and metastatic prostate cancer. These results lend support that genomic profiling for advanced prostate cancer may identify actionable targets not routinely used in the current metastatic paradigm.

Correlation between DIDO1 variation and MSI-status in colorectal cancer.

e16054 Background: Several studies have displayed a sustained clinical response to immune checkpoint inhibitors with profound clinical improvement in patients with microsatellite instability-high (MSI-H) metastatic colorectal cancer (CRC). MSI-H tumors may display higher numbers of TILs, many of which can be directed against tumor-related neoantigens. We set out to examine the underline mechanism in gene level to further explain the differences between MSI-H and MSS CRC. Methods: Whole exome sequencing(WES) was performed on 68 CRC patient.MSI status of these patients were determined using a targeted next generation sequencing panel covering 100 MSI loci. TCGA database was used to analyze WES data of 364 CRC patients with different MSI states, and immune signature was used to analyze the corresponding relationship of immune cell expression in different populations. Results: Of 56 MSS patients, 58.9% (33/56) had copy number variants (CNV) in DIDO1, and 1.8 (1/56) had single nucleotide variants(SNV) in DIDO1. Of 12 MSI-H patients, 33.3% (4/12) had SNV in DIDO1 gene, None had CNV in DIDO1. TCGA database showed that of 308 MSS patients, 8% (24/308) had CNV in DIDO1 and 3% (9/308) had SNV in DIDO1. Of 56 MSI-H patient, 39% (22/56) had SNV in DIDO1 and only one patent had both SNV and CNV in DIDO1. Gene variation of DIDO1 of 68 CRC patients showed a correlation with TCGA database. Gene variation of DIDO1 in MSI-H patients are mainly SNV, and the incidence of CNV is very small (4.3% of DIDO variation).While, gene variation of DIDO1 in MSS patients are mainly CNV, followed by SNV, indicating DIDO1 CNV are highly possible occurring in MSS patients. Furthermore we analyzed the relationship between the copy number of DIDO1 and immune signature through CRC TCGA database. The results showed increase of DIDO1 copy number was negatively correlated with the abundance of NK cells (P = 0.00048), T cells (P = 8.23×10-5) and macrophages (P = 1.75×10-8). Conclusions: Our results showed that different MSI status display unique patent of DIDO1 gene variation, which may be related to different immune micro environment among MSI-H/MSS patients.

Immune subtype of mismatch repair deficient colorectal carcinoma.

e15194 Background: Half of microsatellite instability-high (MSI-H) colorectal carcinoma (CRCs) patients do not response to checkpoint blockade (ICB) immunotherapy. We aimed to unleash the underlying mechanism of distinct efficacy to ICB by sophisticated depicting the immune microenvironment of MSI-H CRC. Methods: Public omics and clinical data of patients with MSI labels were collected from TCGA data portal (364 samples) and Gene Expression Omnibus (GSE39582, GSE13294, GSE13067, GSE35896, GSE24514, GSE25071, GSE79959, GSE103340, GSE29638, GSE33113 cohorts, 1119 samples). GEO datasets were used as discovering sets, and TCGA dataset was used as validating sets. The immune cell infiltrations and signaling pathways in the tumor microenvironment were quantified by single sample Gene Set Enrichment Analysis (ssGSEA), and the bio-similarities were estimated by t-Distributed Stochastic Neighbor Embedding (tSNE). Clustering was identified by k-mean unsupervised strategy with optimal k. Statistical analysis and data visualization were all carried out using the R. Results: Based on the whole transcriptome and immune cell infiltration profiling, both GEO and TCGA cohorts showed that MSI-H patients harbored unique pattern which significantly differed from the MSS counterpart. Unsupervised clustering further classified the MSI-H patients into “Hot” and “Cold” subgroups with remarkable different IFNG-related signatures, inflammatory response score, interferon-γ signaling score, and survival outcome. Screening assay identified 23 genes ( ADAMTSL3, DLGAP4, DNAH11, FFAR3, GABRA4, KCNA6, KCTD9, KIAA1033, KLHL6, LARGE, MORC1, NDST3, OR5H14, PAX5, PHF3, PIK3R5, RNF25, SPATA20, STAT4, TLR9, TMC3, TTC12, ZNF790) enriched and 5 genes ( CELSR3, DGKD, HECTD4, RECQL4, SLC9A4) spared in immune “hot” tumors. Moreover, “hot” tumor showed less WNT signaling pathway score, which was negatively correlated with the IFNG signaling and inflammatory response within the MSI-H CRC tumors. Conclusions: We firstly identified immune hot and cold groups from MSI-H CRCs, which may be related to different immunotherapy response. This result may help further understanding the anti-immunotherapy of MSI-H CRCs.

MSI/MMR test usage and checkpoint inhibitor practices in Europe.

e19327 Background: Micro-Satellite Instability (MSI) or DNA Mismatch Repair (MMR) is an established prognostic test associated with response to chemotherapies in Lynch Syndrome, colorectal cancer and other indications. Recently, MSI/MMR status has been shown to predict response to immune checkpoint inhibitors (CPI). Pembrolizumab has been approved in the USA for MSI-high or mismatch repair deficient patients for all indications. A similar approval has not been obtained in the EU. This data research project examined MSI/MMR testing in Europe and its possible association with use of CPI therapies. Methods: This study was conducted using Oncology Dynamics, an IQVIA oncology cross-sectional survey, collecting anonymized real-world patient-level data. 97,807 and 96,111 drug treated patients for solid tumors in 2018 &amp; 2019, respectively, were collected across 5 European countries (France, Germany, Great Britain, Italy and Spain). Data included number of patients tested for MSI/MMR, results of the test, site and funding type, and the drug(s) prescribed. Results: European MSI/MMR test rates ranged from 3% in Italy in 2018 to 12% in France in 2019. Testing rates increased modestly in all countries over the period. Testing rates were determined in 25 specific indications plus all other indications. As expected, rates were highest in colorectal and stomach cancer. Testing was observed in other indications including Esophageal, Brain and Melanoma all with rates of 10% or higher. The percentage of MSI-High patients ranged from a low of 13% in Italy in 2019 to 26% in France in 2019. Finally, 17% of MSI-High patients are treated with CPIs compared to 5% of MSI-Low patients across all countries in 2019. Conclusions: The results over two years and almost 200,000 patients present insights into the use of MSI testing in 5 European countries. MSI testing is performed in many indications in addition to those typically associated with the biomarker. The increase in CPI use in MSI-High patients suggest that test results may impact use of checkpoint inhibitors although causation may not be inferred from the current analysis. However, the correlation suggests that further analysis is warranted.

The association of molecular biomarkers with efficacy of pembrolizumab versus paclitaxel in patients with gastric cancer (GC) from KEYNOTE-061.

4512 Background: KEYNOTE-061 (NCT02370498) was a randomized, open-label, phase 3 study of pembrolizumab vs paclitaxel in patients with advanced gastric or gastroesophageal junction adenocarcinoma with tumor progression after first-line therapy (N =592). We explored the association of tissue tumor mutational burden (tTMB) status and clinical outcomes in patients with GC enrolled in KEYNOTE-061, including the relationship with PD-L1 combined positive score (CPS) and microsatellite instability-high (MSI-H) status. Methods: In patients from KEYNOTE-061 with evaluable tumor and matched normal whole exome sequencing (WES) data (N = 420; pembrolizumab, 218; paclitaxel, 202), the association of tTMB (continuous log10 scale) with confirmed ORR and PFS by blinded central radiology review per RECIST v1.1, and OS was evaluated within each treatment arm using logistic regression (ORR) and Cox proportional hazards regression (PFS; OS). The clinical utility of tTMB was assessed using the prespecified cutoff of 175 mut/exome. Clinical data cutoff: October 26, 2017. Results: tTMB was significantly associated (α=0.05) with ORR, PFS, and OS in patients treated with pembrolizumab (one-sided P&lt;0.001) but not paclitaxel (two-sided P&gt;0.600). The area under the receiver operating characteristics curve for tTMB and response (pembrolizumab vs paclitaxel) was 0.68 (95% CI, 0.56-0.81) vs 0.51 (95% CI, 0.39-0.63). Patient outcomes by tTMB cutoff are reported in Table. There was low correlation between tTMB and PD-L1 CPS in both treatment arms (r&lt;0.18). tTMB remained significantly associated with all clinical end points with pembrolizumab after adjusting for PD-L1 CPS and with PFS and OS after excluding MSI-H patients. Conclusions: This exploratory analysis from KEYNOTE-061 is the first to demonstrate a strong association between tTMB and response to pembrolizumab in patients with GC. Data further suggest tTMB is a significant and independent predictor beyond PD-L1 status. Clinical trial information: NCT02370498 . [Table: see text]

BRAF-V600E and microsatellite instability prediction through CA-19-9/CEA ratio in patients with colorectal cancer.

Early identification of colorectal cancer (CRC) patients that are BRAF-V600E mutant and/or microsatellite instability-high (MSI-High), has both prognostic and predictive value. We wanted to highlight an observation of utilizing 2 simple, rapid and universally available lab tests, i.e., carbohydrate cancer antigen 19-9 (CA 19-9) and carcinoembryonic antigen (CEA) tumor markers, the ratio (CA-19-9/CEA) of which can distinctly identify these patients from other molecular subsets of CRC. All patients with metastatic CRC from December 2016 to February 2019 were identified, and included in the study if they had both CA19-9 and CEA tests available. Circulating tumor DNA (ctDNA) testing and tissue genetic testing results were used to categorize patients into BRAF V600E microsatellite stable (MSS), MSI-High, RAS mutant MSS and RAS/RAF wild type CRCs. Kruskal-Wallis test was used to compare the CA19-9/CEA ratio between mutation types and the pairwise p values were adjusted for multiple comparisons with Holm method. For sensitivity analysis, the same analysis was repeated for the mean and median ratio of each patient. All tests were two-sided with alpha level set at 0.05 for statistical significance. BRAF-V600E MSS CRC patients had a discordantly profound elevation in CA-19-9 levels as opposed to the CEA levels. Patients in the BRAF V600E MSS subset had the highest median CA19-9/CEA ratio versus the least median ratio in MSI-High patients. The median of maximum CA-19-9/CEA ratio was 28.92 (range, 2.76-707.27) in BRAF-V600E MSS patients and 4.06 (range, 0.46-166.74) in MSI-High subset of patients. To date, this is the first report utilizing the ratio of tumor markers CA19-9/CEA as a predictive rather than just prognostic tool to identify BRAF-V600E MSS and MSI-High CRC patients.

Clinicopathological features of Egyptian colorectal cancer patients regarding somatic genetic mutations especially in KRAS gene and microsatellite instability status: a pilot study

BackgroundColorectal cancer (CRC) is the third most common cause of cancer-related deaths which contributes to a significant public health problem worldwide with 1.8 million new cases and almost 861,000 deaths in 2018 according to the World Health Organization. It exhibits 7.4% of all diagnosed cancer cases in the region of the Middle East and North Africa. Molecular changes that happen in CRCs are chromosomal instability, microsatellite instability (MSI), and CpG island methylator phenotype. The human RAS family (KRAS, NRAS, and HRAS) is the most frequently mutated oncogenes in human cancer appearing in 45% of colon cancers. Determining MSI status across CRCs offers the opportunity to identify patients who are likely to respond to targeted therapies such as anti-PD-1. Therefore, a method to efficiently determine MSI status for every cancer patient is needed.ResultsKRAS mutations were detected in 31.6% of CRC patients, namely in older patients (p = 0.003). Codons 12 and 13 constituted 5/6 (83.3%) and 1/6 (16.7%) of all KRAS mutations, respectively. We found three mutations G12D, G12C, and G13D which occur as a result of substitution at c.35G>A, c.34G>T, and c.38G>A and have been detected in 4/6 (66.6%), 1/6 (16.7%), and 1/6 (16.7%) patients, respectively. Eleven (57.9%) patients had microsatellite instability-high (MSI-H) CRC. A higher percentage of MSI-H CRC was detected in female patients (p = 0.048). Eight patients had both MSI-H CRC and wild KRAS mutation with no statistical significance was found between MSI status and KRAS mutation in these studied patients.ConclusionIn conclusion, considering that KRAS mutations confer resistance to EGFR inhibitors, patients who have CRC with KRAS mutation could receive more tailored management by defining MSI status. MSI-high patients have enhanced responsiveness to anti-PD-1 therapies. Thus, the question arises as to whether it is worth investigating this association in the routine clinical setting or not. Further studies with a larger number of patients are needed to assess the impact of MSI status on Egyptian CRC care.

Clinical and Molecular Predictors of Response to Immune Checkpoint Inhibitors in Patients with Advanced Esophagogastric Cancer.

Immune checkpoint inhibitors (ICI) are effective in only a minority of patients with esophagogastric cancer (EGC). Here, we aimed to identify predictors of durable clinical benefit to ICI in EGC. Patients with advanced EGC treated with ICIs at Memorial Sloan Kettering Cancer Center (New York, NY) were identified. Clinicopathologic variables were assessed. In patients profiled by MSK-IMPACT-targeted sequencing, outcomes were correlated with tumor genomic features. One-hundred sixty-one patients were treated with ICIs (110 with anti-PD-1/PD-L1 antibodies and 51 with anti-CTLA-4 and PD-1/PD-L1 antibodies). The median progression-free survival (PFS) and overall survival (OS) were 1.7 and 4.9 months, respectively. Greater number of disease sites (≥3), liver metastases, treatment with ≥3 prior therapies and ECOG performance status ≥2 were associated with poorer PFS and OS. Patients treated with combination ICI and those with PD-L1-positive tumors had improved outcomes. There was no difference in outcomes between patients treated with antibiotics during or in the 2 months preceding ICI treatment versus those who were not. Occurrence of irAEs was associated with improved OS. In genomically profiled tumors (n = 89), survival was associated with increasing tumor mutation burden (TMB). However, in multivariable analyses and when microsatellite unstable (MSI) patients were excluded, a significant association was no longer observed. In patients with advanced EGC, heavily pretreated patients, those with high-volume disease and/or poor PS were less likely to benefit from ICI. irAEs were associated with improved OS. TMB correlated with improved survival, but this association was not observed when MSI-high patients were excluded.

Tumor Infiltrating Lymphocytes and Macrophages Improve Survival in Microsatellite Unstable Colorectal Cancer

Due to the loss of DNA repair mechanisms in colorectal cancer (CRC) with microsatellite instability (MSI), somatic mutations accumulate within DNA; making them more prone to attack by tumor infiltrating lymphocytes (TIL) and macrophages. We hypothesize that MSI-High (MSI-H) patients have favorable survival due to increased tumor immunogenicity. The Cancer Genome Atlas (TCGA) was used to evaluate gene expression from 283 patients with CRC, comparing MSI-H and microsatellite stable (MSS) patients. CIBERSORT algorithm estimated the fraction of immune cell types. We found that low expression of DNA repair genes (MLH1, MLH3, PMS1, PMS2, ATR, PRKDC, ATM, BRCA2) associated with MSI-H. MSI-H was directly associated with Helper T-cells (p = 0.034) and M1 macrophages (p < 0.0001). MSI-H tumors associated with diminished intra-tumoral heterogeneity as well as higher expression of checkpoint molecules PD-1, PD-L1, CTLA4, LAG3 and TIM3 (p < 0.0001). Improved OS was seen in patients with low ATM, PMS2 and MLH3. In the TCGA CRC cohort, decreased expression of DNA repair genes associated with MSI-H. MSI-H patients had improved survival, likely due to higher TIL and M1 macrophage infiltration as well as lower intra-tumoral heterogeneity. MSI-H also associates with expression of immune checkpoint molecules with potential for development of therapeutic targets.

A Pilot Study of Stereotactic Body Radiotherapy (SBRT) Combined with a PD-L1 Antibody Durvalumab (D) and a CTLA-4 antibody Tremelimumab (T) To Treat Metastatic Anaplastic Thyroid Cancer (ATC)

The prognosis of metastatic ATC is dismal and there are very limited treatment options. The thyroid is one of the most immunogenic organs in the body. PD-L1 is commonly expressed on ATC tumor cells and PD-1 in the inflammatory cells in the ATC microenvironment. However, antibodies to PD-1 as single agents have a poor record in this disease. Therefore, we designed this pilot study to add T to D and together with SBRT to augment their effects in hope to improve survival. This study evaluated the addition of T (75 mg every 4 weeks up to 4 doses) to D (1500 mg every 4 weeks). SBRT 9Gy x 3 fractions was given within the first 2 weeks of treatment to produce an “abscopal” effect. Major inclusion criteria: Metastatic ATC; ECOG PS 0-2; No prior immunotherapy; Last anti-cancer treatment > 7 days prior to starting study. Primary objective 1-year overall survival with target of ≥ 2 out of 12 patients. 12 patients were accrued. Male – 50%; Median PS 1; Median Age – 71 (49-82); Prior radiation to neck (75%); Prior chemotherapy (75%). MSI-High was noted in 2/11 subjects. BRAFV600E mutation in 3/12 subjects. There were 0 confirmed responses and only 1 subject with SD for 4 cycles or longer. Median time on treatment was 11 weeks (1-28+ weeks). MSI status did not affect treatment response. MSI-High patients were on treatment before progression for 8-14 weeks. Median overall survival was 14.5 weeks with only one person alive past 1 year. Neither the presence of a BRAF or p53 mutation appeared to affect either outcome. T/D with SBRT was not active in metastatic ATC. Future studies looking at other novel immunotherapy combinations in ATC should be evaluated. Biopsies done on study are being analyzed and will be presented.

BRAF-V600E and microsatellite instability prediction through CA-19-9/CEA ratio in patients with colorectal cancer.

e15065 Background: Colorectal cancer (CRC) is a heterogeneous disease. Specifically for patients with BRAF-V600E mutations and/or mismatch repair deficiency or microsatellite instability-high (dMMR/MSI-High), there have been significant advances in terms of treatment options. Early identification of these subsets of patients has both prognostic and predictive value. We wanted to highlight an observation of utilizing 2 simple, rapid and universally available lab tests i.e. carbohydrate cancer antigen 19-9 and carcinoembryonic antigen tumor markers, the ratio (CA-19-9/CEA) of which can distinctly identify these patients. Methods: We included and analyzed the ratio of CA-19-9/CEA levels in patients with metastatic CRC at Mayo Clinic from December 2016 to February 2019, where both the results were available. Non-parametric tests were done to compare and contrast the differences in the median ratio and tumor marker levels. Results: BRAF-V600E mutant CRC patients had a discordantly profound elevation in CA-19-9 levels as opposed to the CEA levels. The median CA-19-9/CEA ratio was 20 (range: 0.3-167.3) in BRAF-V600E MSS patients as opposed to 4.40 (range: 0.003-216.2) in all other patients, p-value of 0.007 (Table). Similarly, the mean CA-19-9/CEA ratio for BRAF V600E MSS tumors was 57.15 (S.D.± 62.76) versus 10.5 (S.D.± 33.90) for all other types. Furthermore, this discordant elevation is not seen in BRAF-mutant MSI-High or any MSI-High patients (median CA-19-9/CEA ratio - 0.46). Conclusions: To date, this is the first report utilizing the ratio of tumor markers CA-19-9/CEA as predictive rather than just prognostic markers. It clearly identifies BRAF-V600E MSS and the MSI-High CRC patients from other subsets.[Table: see text]

Pilot study combining PD-L1 antibody durvalumab (D) with CTLA-4 antibody tremelimumab (T) and stereotactic body radiotherapy (SBRT) to treat metastatic anaplastic thyroid cancer (ATC).

6088 Background: ATC is a rare and aggressive cancer with very limited treatment options. The thyroid is one of the most immunogenic organs in the body and PD-L1 is commonly expressed on ATC tumor cells and PD-1 in the inflammatory cells in the ATC microenvironment. However, antibodies to PD-1 as single agents have a poor record in this disease. Methods: This study evaluated the addition of T (75 mg every 4 weeks up to 4 doses) to D (1500 mg every 4 weeks). SBRT 9Gy x 3 fractions was given within the first 2 weeks of treatment to produce an “abscopal” effect. Major inclusion criteria: Metastatic ATC; ECOG PS 0-2; No prior immunotherapy; Last anti-cancer treatment &gt; 7 days prior to starting study. Primary objective 1-year overall survival with target of ≥ 2 out of 12 patients. Results: 12 patients were accrued. Male – 50%; Median PS 1; Median Age – 71 (49-82); Prior radiation to neck (75%); Prior chemotherapy (75%). MSI-High was noted in 2/11 subjects. BRAFV600E mutation in 3/12 subjects. There were 0 confirmed responses and only 1 subject with SD for 4 cycles or longer. Median time on treatment was 11 weeks (1-28+ weeks). MSI status did not affect treatment response. MSI-High patients were on treatment before progression for 8-14 weeks. Median overall survival was 14.5 weeks with only one person alive past 1 year. Neither the presence of a BRAF or p53 mutation appeared to affect either outcome. Conclusions: T/D with SBRT was not active in metastatic ATC. Future studies looking at other novel immunotherapy combinations in ATC should be evaluated. Biopsies done on study are being analyzed. Clinical trial information: NCT03122496.

CLO19-045: Safety of Immune Checkpoint Inhibitors in Cancer Patients With Microsatellite Instability-High (MSI-H) Status: An Experience From Qatar

Background: Microsatellite instability-high (MSI-H) is shown to predict response to the immune checkpoint inhibitors (ICPi). Recently, the FDA granted an accelerated approval for the use of pembrolizumab in any solid tumor and nivolumab in metastatic colorectal cancer in patients with MSI-H. However, the immune-related adverse events (irAEs) exhibit a unique heterogeneous spectrum than conventional chemotherapy adverse drug reactions (ADRs). Underestimating the irAEs could be potentially lethal. Objectives: To evaluate the irAEs; their management, and outcome in MSI-H patients treated with ICPi at the National Center for Cancer Care and Research (NCCCR) in Qatar. Methods: All patients with MSI-H and treated with ICPi at the NCCCR between January 2015 and June 2018 were reviewed retrospectively. Radiologic assessment of irAEs and Naranjo score were used to estimate and confirm the probability of ADRs. Patient demographics, immunotherapy treatment, reported irAEs, and their management were collected. Results: Of the total cohort of patients receiving ICPIs; 9 patients with MSI-H were identified; all received pembrolizumab. 45% (n=4) of the patients were still actively on treatment; 22% (n=2) received only 1 dose then passed away; 22 % (n=2) discontinued because of disease progression; and 11% (n=1) of the patients received 2 cycles as neoadjuvant treatment. To the best of our knowledge, this is the biggest cohort of cancer patients with MSI-H in the Middle East. Calculated Naranjo score was 7 in 45% of the patients (n=4) and 5 in 22 % of patient (n=2), which indicates a probable ADR. 34% of the patients (n=3) did not experience ADRs till the date of data cutoff. 8 irAEs were seen in 67% (n=6) of the patients (Table 1). Based on laboratory or radiologic confirmation, 87.5% (n=7) were irAEs and 12.5% (n=1) was not related to pembrolizumab. Laboratory findings confirmed 25% of the ADRs and radiologic findings confirmed 75% of the ADRs. Of those who developed irARs, 3 patients required a hold of treatment, 1 needed monitoring, and 2 required pharmacologic interventions. There was one patient who received empirical pharmacologic intervention at which evaluation showed no relation to immunotherapy. Conclusion: irAEs can sometimes be unpredictable, rare, and often missed. Frequent monitoring and early management of these suspected or confirmed adverse effects is life saving and should be done in a multidisciplinary approach.

Evaluation of prognostic effects of MSI, PD-L1 and TIL in resected bladder cancer.

465 Background: The aim of the study was evaluating prognostic significance of tumor infiltrating lymphocytes (TIL), microsatellite instability (MSI) and programmed cell death ligand-1 (PD-L1) expression which are used as predictive biomarkers in immunotherapy. Methods: Clinic and pathologic features of bladder cancer patients who were underwent radical cystectomy were retrospectively analyzed from patients’ records in this single-center study. PD-L1, PD-L1 in TIL, PMS2, MSH2, MSH6 and MLH1 immunohistochemistry staining were carried out to archived resected tumor specimens of the eligible patients. MSI was evaluated according to existing of PMS2, MSH2, MSH6 and MLH1. Results: Fifty-six males (91.8%) and 5 females (8.2%) of total 61 patients were eligible for the study. Median age was 61.72 (35-81). PD-L1 expression in tumor cells and PD-L1 expression in TIL were positive in 14,8% (n = 9) and 16.4% (n = 10) of total 74 patients, respectively. MSI was high in 15 patients (24.6%). Intratumoral TIL rate was &lt; 10% in 49 patients (80.3%) while &gt; 10% in 12 patients. (19.7%) In Chi-square test, there was no statistically significant relationship between PD-L1, PD-L1 in TIL, MSI and TIL rate and patients’ characteristics including sex, stage, pathologic grade and lymph node status. Three-years overall survival (OS) rate was calculated as 43%. Univariate analysis did not reveal any significant difference in 3-years OS in PD-L1 expression in tumor, PD-L1 expression in TIL and TIL rate &gt; 10% . (p = 0.822, p = 0.638, p = 0.318; respectively ). There was a positive trend with MSI high patients and OS (p = 0.089). At also; age and stage showed statistically significant difference in multivariate analysis. (p = 0.023, p = 0.011, respectively). Conclusions: This study revealed that there is no prognostic significance of PD-L1 and TIL. However, there are positive trend between OS and MSI, which is proven as predictive biomarker of immunotherapy, in patients who were followed with same treatment and follow-up approach in single center. These results must be corroborated with large and prospective investigations in order to better understanding biology and behavior of bladder cancer.

Pembrolizumab in advanced recurrent endometrial cancer: A cost-effectiveness analysis

ObjectiveTo determine the cost-effectiveness of pembrolizumab in patients with recurrent endometrial cancer that have failed first-line chemotherapy. MethodsWe created a model to evaluate the cost-effectiveness of pembrolizumab compared to pegylated liposomal doxorubicin (PLD) or bevacizumab for the treatment of women with recurrent endometrial cancer who have failed carboplatin and paclitaxel. Microsatellite instability-high (MSI-H) and non-microsatellite instability-high (non-MSI-H) tumors were evaluated. We included 4400 patients in the model; 800 patients were assumed to have MSI-H tumors. Drug costs were calculated using 2016–2017 wholesale acquisition costs, and cost of Grade III-IV toxicities was estimated from clinical experience. Effectiveness was calculated as 2-year overall survival (OS). We calculated incremental cost-effectiveness ratios (ICERs) to determine the cost per 2-year survivor. Univariate sensitivity analyses were performed. The willingness to pay threshold was $100,000 per year of OS. ResultsThe cost of therapy with PLD and bevacizumab were $33.2 million (M) and $167.9 M, respectively. The cost of pembrolizumab therapy was $318.3 M for non-MSI-H patients compared to $57.9 M for MSI-H patients. For non-MSI-H patients, bevacizumab was cost-effective relative to PLD with an ICER of $153,028, while pembrolizumab was not cost-effective relative to bevacizumab with an ICER of $341,830. For MSI-H patients, pembrolizumab was cost-effective compared to PLD with an ICER of $147,249, while bevacizumab was subjected to extended dominance. Sensitivity analysis revealed that for non-MSI-H patients, one cycle of pembrolizumab would need to cost $7253 or less to be cost-effective. ConclusionsFor patients with MSI-H recurrent endometrial cancers who have failed first-line chemotherapy, pembrolizumab is cost-effective relative to other single agent drugs. To be cost-effective in non-MSI-H patients, the cost of pembrolizumab should decrease substantially.

Safety and clinical activity of durvalumab monotherapy in patients with microsatellite instability–high (MSI-H) tumors.

670 Background: MSI-H tumors have shown to be responsive to PD-1 inhibitor therapy. We evaluated the anti-PD-L1 mAb durvalumab in patients with MSI-H tumors, in two ongoing studies: a phase 1/2, multicenter, open-label study in patients with advanced solid tumors, and a phase 2 single-center study in patients with advanced colorectal cancer (CRC). Methods: Patients with MSI-H tumors (determined locally by immunohistochemistry or sequencing) received durvalumab 10 mg/kg IV every 2 weeks for 12 months or until confirmed progressive disease, whichever was first. Objectives were to evaluate safety and antitumor activity (per investigator-assessed RECIST v1.1). Results: As of Oct 16, 2017, 62 MSI-H patients (97% with prior anti-cancer therapy) received treatment in the multicenter study; median duration of follow-up was 29 months. Treatment-related adverse events (TRAEs) occurred in 37 patients (60%), most commonly diarrhea (15%), asthenia (11%), fatigue (11%), nausea (10%), and hypothyroidism (10%). Grade 3/4 TRAEs occurred in 2 patients (3%). There were no deaths or treatment discontinuations due to TRAEs. Objective response rates (ORR) were 23% for the total population and 22% for patients with CRC; 9 of 14 responders were ongoing at data cutoff. As of Sep 13, 2018, 11 patients with MSI-H CRC were treated in the single-center study; median duration of follow-up was 30 months. One patient discontinued treatment due to treatment-related aseptic meningitis (resolved with steroids); response rate and survival were similar to the multicenter study (Table). Conclusions: Durvalumab had a tolerable safety profile, and showed promising antitumor activity and overall survival in patients with MSI-H tumors. Clinical trial information: NCT01693562 and NCT02227667. [Table: see text]

Issue Highlights

Issue Highlights

Fusion Kinases Identified by Genomic Analyses of Sporadic Microsatellite Instability-High Colorectal Cancers.

Colorectal cancers with microsatellite instability-high (MSI-H) status, due to mismatch repair deficiency, are associated with poor patient outcomes after relapse. We aimed to identify novel therapeutic targets for them. We performed MSI analyses of over 2,800 surgically resected colorectal tumors obtained from consecutive patients treated in Japan from 1998 through June 2016. Whole-exome sequencing, transcriptome sequencing, and methylation analyses were performed on 149 of 162 tumors showing MSI in BAT25 and BAT26 loci. We analyzed patient survival times using Bonferroni-adjusted log-rank tests. Sporadic MSI-H colorectal cancers with promoter methylation of MLH1 (called MM) had a clinicopathological profile that was distinct from that of colorectal cancers of patients with germline mutations (Lynch syndrome, LS-associated) or somatic, Lynch-like mutations in mismatch repair genes. MM tumors had more insertions and deletions and more recurrent mutations in BRAF and RNF43 than LS-associated or Lynch-like MSI-H tumors. Eleven fusion kinases were exclusively detected in MM MSI-H colorectal cancers lacking oncogenic KRAS/BRAF missense mutations and were associated with worse post-relapse prognosis. We developed a simple method to identify MM tumors and applied it to a validation cohort of 28 MSI-H colorectal cancers, identifying 16 MM tumors and 2 fusion kinases. We discovered that fusion kinases are frequently observed among sporadic MM MSI-H colorectal cancers. The new method to identify MM tumors enables us to straightforwardly group MSI-H patients into candidates of LS or fusion kinase carriers.