Intermediate Tumor Mutational Burden Research Articles

Abstract 2150: CLDN18/ARHGAP26 fusions in gastric cancers

Abstract Background Previous work has shown that young females, who present with genomically-stable, poorly-differentiated, diffuse gastric cancer harbor CLDN18/ARHGAP26 fusions more often than older individuals with intestinal type or non-diffuse gastric cancer histology. This fusion usually occurs between exon 5 of CLDN18 and exon 12 of ARHGAP26, is associated with a poor prognosis, and confers a propensity for metastasis. We investigated the prevalence of this fusion and characterized the fusion-positive patient population among gastric cancer patients whose tumor samples underwent OncoExtraTM assay testing. Methods Tumor and paired-normal samples from 171 gastric cancer patients aged 18-90 years were sequenced with the OncoExtraTM assay. This assay uses whole-exome DNA sequencing to detect somatic single base substitutions, indels, copy number alterations, and whole transcriptome RNA sequencing to detect gene fusions and alternative transcripts. The RNA sequencing data were used to identify CLDN18/ARHGAP26 fusions. Results The 171 patients were well balanced between sexes: 91 (53.2%) men, 80 (46.8%) women. Most patients were older: 44 (25.7%) ≤50 years old, 127 (74.3%) >50 years old. There were 6 (3.5%) patient samples with a CLDN18/ARHGAP26 fusion. The fusion was found more often in females (5 of 80, 6.3%) than males (1 of 91, 1.1%) and younger patients (3 of 44, 6.8%, ≤50 years; 3 of 127, 2.3%, >50 years). All 6 had diffuse histology by pathology, variably described as poorly differentiated, diffuse, or signet ring subtype. Notably, the 2 patients with mixed histology did not have metastases reported on the pathology report, while the 4 whose histology was described as diffuse or signet ring cell type were metastatic. In all cases the fusion involved exon 5 of CLDN18 and exon 12 of ARHGAP26. Further analysis revealed that five of the fusion-containing tumors had alterations in genes/pathways known to be oncogenic drivers of cell proliferation, specifically 1 ERBB2 (2 mutations present), 1 SWI/SNF pathway (ARID1A and PBRM1 both altered), 2 MET (both amplifications), and 1 PI3K pathway (PI3KCA altered). The sixth tumor sample possessed no obvious driver alterations: only TP53 and WRN were altered. Five of the 6 tumors had low tumor mutational burden (TMB) and were microsatellite stable, the sixth had intermediate TMB, and none had evidence for genomic instability. No CLDN18 fusions were found in any other solid tumors (7050 samples). Conclusions The OncoExtraTM assay detected gastric cancer CLDN18/ARHGAP26 fusions at a frequency (3.5%) similar to previous reports. The majority were female and of younger age compared to patients lacking this fusion. Five of the 6 tumors had additional oncogenic alterations associated with cell proliferation. Given its frequency in poorly differentiated gastric cancer with metastatic potential, as well as its prevalence in a relatively young cohort, this fusion is an attractive target for ongoing drug development. Citation Format: Deborah Josefson, David W. Hall, Jess Hoag, Ariane Kemkes, Janine LoBello, Snehal G. Thakkar, Gargi Basu. CLDN18/ARHGAP26 fusions in gastric cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2150.

Trials in progress: A phase 1, open-label, pharmacokinetic, safety and tolerability study of PF-07265807 (selective TAM kinase inhibitor) alone or with sasanlimab in patients with advanced or metastatic solid tumors.

TPS270 Background: Inhibition of Mer Proto-oncogene tyrosine kinase (MERTK) and AXL may lower the threshold for immune activation thereby promoting anti-tumor activity. PF-07265807 (ARRY-067) is a selective small-molecule inhibitor of the tumor-associated macrophage kinases MERTK and AXL. In preclinical models, PF-07265807 plus anti-programmed cell death protein 1 (anti-PD-1) antibodies show antitumor activity that results in long-term cures and resistance to tumor re-challenge. Sasanlimab is a monoclonal antibody to PD-1 administered subcutaneously (300 mg every 4 wk or equivalent); it has an acceptable safety profile and is being tested in a Phase 3 trial in non-muscle invasive bladder cancer. This first-in-human study will evaluate safety, tolerability, pharmacokinetics and preliminary anti-tumor activity of PF-07265807 alone and with sasanlimab in patients (pts) with selected advanced or metastatic solid tumors. Study design of PF-07265807 monotherapy dose escalation (Part 1) was presented at ASCO 2021 (TPS2671). Here, we describe dose escalation (Part 2) and dose expansion (Part 4) cohorts for the doublet combination of PF-07265807 + sasanlimab. Methods: This is a Phase 1, open-label, multi-center study (NCT04458259) of PF-07265807. Adult pts with selected advanced or metastatic solid tumors who are intolerant or resistant to standard therapy will enroll into doublet therapy dose escalation (Part 2). Pts who are anti-PD-1/PD-L1 treatment naïve with intermediate tumor mutational burden (defined as ≥6 and < 16 microsatellite stable) colorectal cancer (CRC) or PD-L1+ (defined as combined positive score ≥1) gastric cancer will enroll into doublet therapy dose expansion cohorts (Part 4). Other key eligibility criteria: measurable or non-measurable disease by RECIST 1.1; ECOG PS 0–2; adequate bone marrow, renal and liver function; and resolved acute effects of any prior therapy. Each cycle will be 21 days. Treatment will continue until disease progression or unacceptable toxicity, whichever occurs first. The doublet maximum tolerated dose (MTD) will be guided by a Bayesian analysis of dose limiting toxicity (DLT) data for doublet therapy (Part 2). The recommended phase 2 dose (RP2D) will then be determined via holistic data review with/without the MTD identification. Primary endpoints in Part 2 include the incidence of DLTs, adverse events and laboratory abnormalities. After doublet MTD/RP2D is identified in Part 2, the preliminary anti-tumor activity of PF-07265807 + sasanlimab will be explored in Part 4. Primary endpoints in Part 4 include objective response and complete response rates; secondary endpoints include disease control rate and response duration, adverse events and laboratory abnormalities. The study began in Q4 2020 and is recruiting pts. Clinical trial information: NCT04458259 .

Incidence of Microsatellite Instability, Mutational Burden, and Actionable Alterations in Genes of Patients with Metastatic Colorectal Carcinoma: A Study from a Tertiary Care Hospital in India

Background and objective: Tumor mutational burden (TMB) and microsatellite instability (MSI) are predictive clinical markers of responses to immunotherapy in a wide range of advanced cancers, including colorectal cancers. The data about TMB and MSI in Indian patients is scarce. Hence, assessed the incidence of MSI, TMB, and actionable alterations in genes of patients with metastatic colorectal carcinoma. Methods: A single centre, observational, prospective study in newly diagnosed patients (n=60) with colorectal carcinoma were assessed for MSI incidence, mutational burden, and actionable alterations in genes. Results: The TMB ranged between 5.08 and 2391 mutations per megabase, and 12 (20%) had low TMB, 12 (20%) intermediate TMB and 36 (60%) high TMB. The TMB was high in right-sided than left-sided cancer (100% vs. 47%). Three or more two, and one genomic alteration were observed in 26 (44%), 20 (33%), and (20%) patients, respectively. Gene fusion was absent in all 60 patients. Gene mutations were predominant in the left-sided than right-sided but statistically insignificant (p=0.7). APC, TP53, and BRCA2 gene mutations were evident in 46, 28, and 22 patients, respectively. Wild KRAS/NRAS gene alterations were evident in all metastatic cancers (n=22) presented at baseline. There was no significant correlation between the genomic alterations and age, sex, histology, or tumor differentiation. Conclusion: This study highlights the importance of detecting genomic mutations at the earliest. Genomic mutations should form the basis for customizing and exploring newer targeted therapy against the most common genomic alteration like APC, TP53, and RAS mutations to improve outcomes.

A phase 1b study evaluating the safety and preliminary efficacy of berzosertib in combination with gemcitabine in patients with advanced non-small cell lung cancer

ObjectivesBerzosertib (formerly M6620, VX-970) is an intravenous, highly potent and selective, first-in-class ataxia telangiectasia and Rad3-related (ATR) protein kinase inhibitor. We assessed the safety, tolerability, preliminary efficacy, and pharmacokinetics (PK) of berzosertib plus gemcitabine in an expansion cohort of patients with advanced non-small cell lung cancer (NSCLC). The association of efficacy with TP53 status and other tumor markers was also explored. Materials and methodsAdult patients with advanced histologically confirmed NSCLC received berzosertib 210 mg/m2 (days 2 and 9) and gemcitabine 1000 mg/m2 (days 1 and 8) at the recommended phase 2 dose established in the dose escalation part of the study. ResultsThirty-eight patients received at least one dose of study treatment. The most common treatment-emergent adverse events were fatigue (55.3%), anemia (52.6%), and nausea (39.5%). Gemcitabine had no apparent effect on the PK of berzosertib. The objective response rate (ORR) was 10.5% (4/38, 90% confidence interval [CI]: 3.7–22.5%). In the exploratory analysis, the ORR was 30.0% (3/10, 90% CI: 9.0–61.0%) in patients with high loss of heterozygosity (LOH) and 11.0% (1/9, 90% CI: 1.0–43.0%) in patients with low LOH. The ORR was 33.0% (2/6, 90% CI: 6.0–73.0%) in patients with high tumor mutational burden (TMB), 12.5% (2/16, 90% CI: 2.0–34.0%) in patients with intermediate TMB, and 0% (0/3, 90% CI: 0.0–53.6%) in patients with low TMB. ConclusionsBerzosertib plus gemcitabine was well tolerated in patients with advanced, pre-treated NSCLC. Based on the observed clinical efficacy, future clinical trials should involve genomically selected patients.

Abstract 1484: SCD-1 blockade sensitizes triple negative breast cancer to immune checkpoint inhibition

Abstract The increase in fatty acid metabolism is a hallmark of cancer. Stearoyl CoA desaturase (SCD) is an endoplasmic reticulum (ER) enzyme that catalyzes D9 cis désaturation of fatty acyl-CoA substrates. One of its isoforms, SCD1, is overexpressed in several cancers including breast cancer. The higher expression of SCD1 in breast cancer patients correlates with significantly shorter relapse-free and overall survival rates, indicating that SCD1 may be a therapeutic target. We have previously developed and published a novel SCD1 inhibitor, SSI4. Metabolic reprogramming facilitates tumor growth by promoting immune suppression in tumors. Fundamental metabolic processes like fatty acid (FA) metabolism are involved in T cell activation and differentiation and their modulation can differentially affect the development of T helper cell lineages. FA synthesis and oxidation are essential for the development and functioning of CD8+ T memory cells and are contributing factors that influence CD4+ T effector and Treg cell development. These associations between metabolism and immune cells lead us to our hypothesis that aberrant de novo lipogenesis is linked to immune suppression. Thus, SCD1 inhibitors should increase anti-tumor immunity. We evaluated the effect of SSI4-mediated SCD1 inhibition in two mouse triple negative breast cancer cell lines. The data showed that SSI4 stimulates calreticulin (CRT) translocation to cell membrane. CRT is an ER resident protein that translocates to the cell surface under ER stress conditions. Cell surface expression of CRT is known to induce immune responses including phagocytosis, translocation of cancer antigen to the cell surface, and apoptosis. We are currently studying the effect of CRT translocation in our model. A major focus of our project is to assess the efficacy of combination treatment of SSI4 and an immune checkpoint blockade. To this end, this combination therapy synergistically blocked E0771 tumor growth in vivo. Further, to understand the immune responses generated, we performed immunohistochemical analysis of the tumors (day 20 post-treatment) indicating that the combination therapy resulted in higher membrane localized CRT, supporting our rationale that CRT translocation is involved in mediating the anti-tumor responses. Flow cytometry analysis indicated that the combination treatment increased immune cell infiltration. Specifically, SSI4 treatment induced infiltration of double negative T cells, natural killer cells and macrophages, suggesting that it promoted a pro-inflammatory immune response. SSI4 treatment down regulated immune suppressive cells including Tregs, dendritic cells and mesenchymal derived stem cells. The response of cancers with low and intermediate tumor mutational burden such as breast cancer to immune checkpoint inhibition is limited. Our data indicates that combination treatment of SSI4 and anti PD1 is a promising therapeutic strategy. Citation Format: Sneha Vivekanandhan, Justyna Trynda, Laura A. Marlow, Barath shreeder, James L. Miller, Adam M. Kase, Winston Tan, Keith L. Knutson, John A. Copland. SCD-1 blockade sensitizes triple negative breast cancer to immune checkpoint inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1484.

Comprehensive Genomic Profiling (CGP) Informs Molecular Diagnosis, Prognosis, and Therapeutic Decision-Making for Patients with Angioimmunoblastic T-Cell Lymphoma (AITL)

Background: AITL, under the 2016 WHO umbrella classification of nodal peripheral T cell lymphomas (PTCL) with a T follicular helper (TFH) phenotype, accounts for ~20% of all PTCL cases. Genomic analysis has revealed recurrent somatic mutations, such as RhoA G17V, that are hallmarks of AITL. Overlapping genomics have been observed in other PTCL subgroups, such as PTCL not otherwise specified (PTCL-NOS). We and others have reported frequent co-occurrence of RhoA G17V with mutations in the epigenetic regulators TET2 and IDH2R172 in AITL (Morley Blood 2015). Since treatment for the disease remains unsatisfactory, efforts are underway to assess the clinical utility of genomic information to guide therapy. The current study aimed to comprehensively assess the genomic landscape of AITL further, including identification of diagnostically and therapeutically relevant alterations.Methods: We explored the FoundationCORE™ database (Foundation Medicine Inc, Cambridge, MA) for cases assigned as AITL or harboring RhoA G17V positivity irrespective of disease ontology. This led to the inclusion of 42 cases: confirmed AITL (concordant diagnoses by internal and external pathologists, 29), suspected AITL (discordant diagnoses, 9), lymph node lymphoma NOS (PTCL, 1), or other neoplasm [pleomorphic myxofibrosarcoma (MFS), 1; marginal zone lymphoma (MZL), 1; cutaneous T-cell lymphoma (CTCL), 1]. Median cohort age was 65.5 years, 65 years for the AITL-specific subset; range for both, 34-88y. Pathology reports indicated Epstein-Barr virus positivity in 16/38 of AITL cases and prior autologous stem cell transplant in 4/38. DNA and RNA were extracted from formalin-fixed paraffin embedded samples or peripheral blood, and CGP performed using the CLIA-certified, NYS-approved, CAP-accredited FoundationOne® Heme assay (He Blood 2016).Results: RhoAG17V was seen in 57% (24/42) of cases in the cohort, including 53% (20/38) of AITL samples and in 1 case each of MFS, MZL, CTCL, and PTCL. Confirmed AITL harbored RhoAG17V in 52% (15/29), and suspected AITL in 56% (5/9), of samples. TET2 mutations (m TET2) were found in 89% of AITLs (26/29, confirmed; 8/9, suspected), and in 1/1 PTCL; as reported previously, m TET2 was not identified in the MFS, MZL, or CTCL. IDH2 mutations (m IDH2), all occurring at R172, were seen in 16% (6/38) of AITL cases, with all 6 co-occurring with RhoAG17V plus m TET2 . DNMT3A mutations (m DNMT3A) were seen in 32% (12/38) of AITLs (9/29, confirmed; 3/9, suspected) and in the single PTCL. RhoAG17V co-occurred with m TET2 (but notm DNMT3A orm IDH2) in 26% (10/38), m TET2 plus m DNMT3A in 7.9% (3/38), and m TET2, mDNMT3A, plus m IDH2 in 7.9% (3/38) of cases; all RhoAG17V cases(20/20) co-occurred with m TET2 . TP53 mutation was seen in 21% (8/38) of AITL cases. Other recurrent somatic mutations included BRCA1 or BRCA2 in 7.9% (3/38), CTNNB1 in 7.9% (3/38), and KRAS, ATM or STAT3 in 2.6% (1/38), of AITL samples. Assessment of tumor mutational burden (TMB), a biomarker for checkpoint inhibitor efficacy in solid tumors, revealed low TMB (<6 mutations/Mb) in 8/10 AITL cases and intermediate TMB (TMB-Intermediate, 6-19 mutations/Mb) in 2/10.Conclusion: This study utilized CGP to explore alterations of diagnostic and therapeutic potential in AITL. Confirming prior studies, in a significant proportion of AITL cases RhoAG17V co-occurred with m TET2 and m IDH2 ; all AITL cases positive for RhoAG17V had concurrent m TET2. We also found RhoAG17V, but not m TET2 or m IDH2, in solitary cases of MZL, MCL, and CTCL.Taken together, co-occurrence of RhoAG17V and m TET2 may provide greater specificity for AITL diagnosis than RhoAG17V alone. We also detected putative actionable targets in AITL. While predictors of response to hypomethylating agents (e.g. m TET2, m IDH2) were seen in most cases, a subset were found to have mutations in BRCA1/2 (3 pts), KRAS (1 pt), CTNNB1 (3 pts), or STAT3 (1 pt). These findings suggest alternative therapeutic opportunities in AITL (e.g. inhibitors of PARP, MEK, mTOR, and STAT3). We further report that mutational burden in AITL is generally low; however, a subset of cases (2/10) were TMB-Intermediate. Although the predictive power of TMB in lymphoma is unclear, in some solid tumors TMB-Intermediate status predicts response to immune checkpoint inhibition. In total, our findings highlight the utility of CGP to identify alterations that may influence the clinical management of AITL. DisclosuresMorley:Foundation Medicine: Employment, Other: Stock. He:Foundation Medicine, Inc: Employment, Other: Stock. Bailey:Foundation Medicine: Employment, Other: stock. Nahas:Foundation Medicine inc: Employment, Other: stockholder. Heilmann:Foundation Medicine, Inc: Employment, Other: Stockholder. Chudnovsky:Foundation Medicine, Inc: Employment, Other: Stockholder. Fabrizio:Foundation Medicine, Inc: Employment, Other: Stockholder. Ali:Foundation Medicine, Inc: Employment, Other: Stock. Lipson:Foundation Medicine: Employment, Other: stock. Stephens:Foundation Medicine Inc.: Employment, Equity Ownership. Ross:Foundation Medicine Inc: Employment, Other: stockholder. Miller:Foundation Medicine: Employment, Other: Stock. Severson:Foundation Medicine: Employment, Other: Stock. Vergilio:Foundation Medicine: Employment, Other: Stock. Erlich:Foundation Medicine: Employment, Other: stock. Mughal:Foundation Medicine, Inc: Employment, Other: Stock.

Somatic HLA Class I Loss Is a Widespread Mechanism of Immune Evasion Which Refines the Use of Tumor Mutational Burden as a Biomarker of Checkpoint Inhibitor Response.

Neoantigen presentation arises as a result of tumor-specific mutations and is a critical component of immune surveillance that can be abrogated by somatic LOH of the human leukocyte antigen class I (HLA-I) locus. To understand the role of HLA-I LOH in oncogenesis and treatment, we utilized a pan-cancer genomic dataset of 83,644 patient samples, a small subset of which had treatment outcomes with immune checkpoint inhibitors (ICI). HLA-I LOH was common (17%) and unexpectedly had a nonlinear relationship with tumor mutational burden (TMB). HLA-I LOH was frequent at intermediate TMB, yet prevalence decreased above 30 mutations/megabase, suggesting highly mutated tumors require alternate immune evasion mechanisms. In ICI-treated patients with nonsquamous non-small cell lung cancer, HLA-I LOH was a significant negative predictor of overall survival. Survival prediction improved when combined with TMB, suggesting TMB with HLA-I LOH may better identify patients likely to benefit from ICIs. SIGNIFICANCE: This work shows the pan-cancer landscape of HLA-I LOH, revealing an unexpected "Goldilocks" relationship between HLA-I LOH and TMB, and demonstrates HLA-I LOH as a significant negative predictor of outcomes after ICI treatment. These data informed a combined predictor of outcomes after ICI and have implications for tumor vaccine development.This article is highlighted in the In This Issue feature, p. 211.

Role of ultraviolet mutational signature versus tumor mutation burden in predicting response to immunotherapy.

Hydrophobic neoantigens are more immunogenic because they are better presented by the major histocompatibility complex and better recognized by T cells. Tumor cells can evade the immune response by expressing checkpoints such as programmed death ligand 1. Checkpoint blockade reactivates immune recognition and can be effective in diseases such as melanoma, which harbors a high tumor mutational burden (TMB). Cancers presenting low or intermediate TMB can also respond to checkpoint blockade, albeit less frequently, suggesting the need for biological markers predicting response. We calculated the hydrophobicity of neopeptides produced by probabilistic in silico simulation of the genomic UV exposure mutational signature. We also computed the hydrophobicity of potential neopeptides and extent of UV exposure based on the UV mutational signature enrichment (UVMSE) score in The Cancer Genome Atlas (TCGA; N = 3543 tumors), and in our cohort of 151 immunotherapy‐treated patients. In silico simulation showed that UV exposure significantly increased hydrophobicity of neopeptides, especially over multiple mutagenic cycles. There was also a strong correlation (R 2 = 0.953) between weighted UVMSE and hydrophobicity of neopeptides in TCGA melanoma patients. Importantly, UVMSE was able to predict better response (P = 0.0026), progression‐free survival (P = 0.036), and overall survival (P = 0.052) after immunotherapy in patients with low/intermediate TMB, but not in patients with high TMB. We show that higher UVMSE scores could be a useful predictor of better immunotherapy outcome, especially in patients with low/intermediate TMB, likely due to increased hydrophobicity (and hence immunogenicity) of neopeptides.

Genomic analysis for potential targetable mutations in relapsed and refractory germ cell tumors.

407 Background: A large number of metastatic germ cell tumors (GCTs) are cured with platinum-based chemotherapy. Patients that have relapsed or refractory disease can be cured with salvage therapy including salvage surgery, standard dose or high-dose chemotherapy with stem-cell transplant. However, 15-20% of patients with metastatic GCT are incurable with current therapeutic options. We sought to perform a genetic analysis on a cohort of these incurable patients to determine the presence of therapeutically targetable genetic mutations. Methods: After obtaining IRB approval, patients treated at Indiana University for refractory or relapsed GCT from 2016-2019 were analyzed with a next-generation sequencing (NGS) platform. Clinically relevant genomic alterations were reviewed to determine the potential for targeted therapies. Results: 10 patients with testicular (9) or ovarian (1) GCT underwent an analysis of tissue (7), blood (1), or both (2) with a mean 2.9 potential targetable mutations per patient. Four patients had NGS from preserved gonadal tissue removed prior to chemotherapy while 6/10 sample specimens were obtained post standard (1) or high-dose (5) chemotherapy. Potential known therapeutic targets were found in 80% (8/10). Of the platforms that tested biomarkers, high microsatellite instability (MSI) (1/5), intermediate tumor mutational burden (1/4), and high PD-L1 expression of 90% (1/3) was appreciated. The MSI-high patient did not respond to pembrolizumab. A patient with a KIT only mutation did not achieve a response to imatinib. One patient with KRAS, KIT, RAF1, CCND2, MET, AR, CDK6, PDGFRA, EGFR, and BRAF mutations was treated with brentuximab and was progression free for 2.5 months. Common mutations were CCND2 (4/10), RAF1 (2/10), KIT (2/10), and KRAS (2/10). Other mutations actionable in non-GCT tumors included ERCC1, TUBB3, RRMI, PIK3CA, TOPO1 and TP53. Conclusions: NGS identifies potential clinically relevant genomic alterations. Genetic mutations may enable future effective therapies as our understanding of platinum-resistant disease evolves. To our knowledge, this is among the first reports utilizing next-generation sequencing in GCT to direct potential therapeutic agents.

Primary CNS lymphoma commonly expresses immune response biomarkers.

BackgroundPrimary central nervous system lymphoma (PCNSL) is rare and there is limited genomic and immunological information available. Incidental clinical and radiographic responses have been reported in PCNSL patients treated with immune checkpoint inhibitors.Materials and MethodsTo genetically characterize and ascertain if the majority of PCNSL patients may potentially benefit from immune checkpoint inhibitors, we profiled 48 subjects with PCNSL from 2013 to 2018 with (1) next-generation sequencing to detect mutations, gene amplifications, and microsatellite instability (MSI); (2) RNA sequencing to detect gene fusions; and (3) immunohistochemistry to ascertain PD-1 and PD-L1 expression. Tumor mutational burden (TMB) was calculated using somatic nonsynonymous missense mutations.ResultsHigh PD-L1 expression (>5% staining) was seen in 18 patients (37.5%), and intermediate expression (1–5% staining) was noted in 14 patients (29.2%). Sixteen patients (33.3%) lacked PD-L1 expression. PD-1 expression (>1 cell/high-power field) was seen in 12/14 tumors (85.7%), uncorrelated with PD-L1 expression. TMB of greater than or equal to 5 mutations per megabase (mt/Mb) occurred in 41/42 tumors, with 19% (n = 8) exhibiting high TMB (≥17 mt/Mb), 71.4% (n = 30) exhibiting intermediate TMB (7–16 mt/Mb), and 9.5% (n = 4) exhibiting low TMB (≤6 mt/Mb). No samples had MSI. Twenty-six genes showed mutations, most frequently in MYD88 (34/42, 81%), CD79B (23/42, 55%), and PIM1 (23/42, 55%). Among 7 cases tested with RNA sequencing, an ETV6-IGH fusion was found. Overall, 18/48 samples expressed high PD-L1 and 38/42 samples expressed intermediate to high TMB.ConclusionsBased on TMB biomarker expression, over 90% of PCNSL patients may benefit from the use of immune checkpoint inhibitors.

1355P - Tumour mutational burden and response to PD-1 inhibitors: An analysis of 89 cases of metastatic melanoma

BackgroundThe era of immunotherapy changed considerably prognosis of melanoma. Nonetheless, only around 40% can get benefit from this treatment, with no biomarkers identified for the therapeutic choice. On the basis of emerging clinical evidence, increased Tumor Mutational Burden (TMB) may be associated with higher sensitivity to immunotherapeutic agents. MethodsThe aim of this study was to analyze in advanced melanoma the relationship between the mutation load and: i) the histologic characteristics, ii) locations according to sun exposure and iii) response to PD-1 inhibitors, in advanced melanoma patients, in a retrospective multicentric analysis by sequencing using FoundationOne®. TMB was characterized as the number of somatic protein-coding base substitution or alterations mutations per megabase (Mb). DNA was extracted from paraffin embedded sections of primary tumor or metastasis. TMB was considered low between 1 and 5 muts/Mb, intermediate between 6 and 19, high if>20 muts/Mb. ResultsIn five centers in France, we included between October 2017 and March 2019 101 patients, aged from 16-year to 92-year-old, with metastatic melanomas. Results were available for 89 cases (12% DNA extraction failure). Acral (n=6, 20%), mucosal (n=5, 17%) and uveal melanoma (n=4, 13%) had a lower TMB compared to sun-exposed melanomas. No melanoma of non-sun-exposed areas had high burden (n=0); intermediate TMB was found in 21% (n=8) and low TMB in 63% of cases (n=19). Conversely, melanoma on chronic exposed areas (face and neck) had high TMB (5/7 cases; 71%). Complete and partial remission after 3 months of anti-PD-1 were more often observed in TMB high patients (n=4;20%) whereas in low and intermediate mutational patients, progression was found in respectively 62% (n=24) and 53% (n=16). ConclusionsTMB is affected by a variety of causes, including ultraviolet light in melanoma and smoking in lung cancer. Desmoplastic melanomas have been reported to have a high prevalence of somatic mutations whereas mucosal and acral have a 5-to 10-fold lower. Our study highlights the importance of TMB with higher response to PD-1 blockade. While it has to be confirmed, sun exposed areas or UV-signature may in be a valuable criterion in helping clinical decision-making. Editorial acknowledgementFoundation One Medicine and Roche Laboratories. Legal entity responsible for the studyFrench hospitals. FundingHas not received any funding. DisclosureC. Allayous: Travel / Accommodation / Expenses: BMS; Travel / Accommodation / Expenses: Roche; Travel / Accommodation / Expenses: Amgen. All other authors have declared no conflicts of interest.

KMT2C mutation associated with tumor mutational burden in small cell lung cancer.

e20098 Background: Immune checkpoint inhibitors are used to treat small cell lung cancer (SCLC). Tumor mutational burden (TMB) emerges as a promising predictor of immunotherapy efficacy, but the relationship between TMB and genetic features of SCLC remains unclear. In this study, we explored the correlation between genetic profiles and TMB in SCLC. Methods: FFPE tumor and matched blood samples were collected from 119 SCLC patients for panel targeted based next-generation sequencing. Genomic alterations (GAs) including single nucleotide variations, short and long insertions/deletions, copy number variations and gene rearrangements were assessed. Results: This study enrolled 114 SCLC and 5 mixed SCLC patients (91 males and 28 females) with a median age of 59 years. Median TMB was 9.3 muts/Mb (25% quantile: 6.3 muts/Mb, 75% quantile: 13.2 muts/Mb). For all patients, 31 (26%) had low TMB (≤6.3 muts/Mb), 55 (46%) had intermediate TMB (6.4-13.1 muts/Mb), and 33 (28%) had high TMB (≥13.2 muts/Mb). KMT2D mutations (mut), included substitution/indel (6/25) and truncation (19/25). KMT2D exhibited substitution/indel (6/25) and truncation (19/25) mutations in 19% of SCLC tumors while KMT2C exhibited substitution/indel (11/17), gene homozygous deletion (1/17) and truncation (5/17) mutations in 12% of SCLC tumors. Tumors with KMT family gene mut (KMT2C and KMT2D) (n = 33) had higher TMB (11.7 vs. 8.5 muts/Mb, p = 0.009). KMT2C mut tumors had higher TMB than KMT2C wildtype (wt) tumors (15.2 vs. 9.2 muts/Mb, p = 0.0036). TP53 mut occurred in 86% of KMT2C mut tumors and KMT2C/TP53 co-mutated tumors had higher TMB than KMT2C wt/TP53 mut tumors (17.8 vs. 9.3 muts/Mb, p = 0.0035) or KMT2C wt/TP53 wt tumors (17.8 vs. 5.4 muts/Mb, p = 0.027). Conclusions: Our data indicates that KMT family genes were frequently mutated in SCLC. KMT2C mut positively correlated with higher TMB and KMT2C co-mutated with TP53 or FAT1 may have a synergic effect on TMB. Our study explored a novel relationship between GAs and TMB that may greatly improve immunotherapeutic strategies for SCLC.

Therapy alteration of solid tumors based on FoundationOne comprehensive genome profiling assay.

e14742 Background: Molecular profiling assays are becoming widely available and provide valuable information on tumor characteristics, which can identify targeted therapies or immunotherapies for cancer patients. However, the clinical utility of such tests remains unclear. Within our institution, we analyzed the clinical utility and subsequent treatment alterations of the FoundationOne Comprehensive Genome Profiling Test (FOne). Methods: We conducted a retrospective cohort review (2017 - 2018) of patients with solid tumors under standard diagnostic care who received FOne testing. We reviewed the therapies that were proposed by FOne and studied whether they led to a therapeutic alteration. Results: 71 patients were identified, of which the majority presented a progressive disease state (80%). Among the cancer types most frequently tested were adenocarcinoma of the colon (14%), prostate (8%), lung (4%), intrahepatic cholangiocarcinoma (8%) and breast invasive ductal carcinoma (4%). In 16 cases (22%), therapies suggested by FOne were approved in patient’s tumor type while in 30 cases (42%) therapies were approved in another tumor type. For an additional 13 cases (18%) only therapies tested in clinical trials were reported. 4 patients (6%) received a new therapy based on the FOne result: cancer of unknown primary (Everolimus due to a TSC1 mutation), cutaneous angiosarcoma (Pembrolizumab due to a high tumor mutational burden (TMB)), gastrointestinal neuroendocrine carcinoma (Ipilimumab and Nivolumab due to an intermediate TMB) and mucinous adenocarcinoma of the appendix (Talazoparib due to an ATM mutation). For 11 cases (15%), a new therapy option was identified by FOne, which due to the current treatment plan might be considered for later use. 3 cases (4%) were evaluated for potential clinical trial enrollment. Note that for an additional 6 patients (8%), the therapies proposed by FOne were already established on the basis of previous testing (e.g. smaller genomic panels, IHC, FISH). Conclusions: Overall, 18 (25%) patients received a new therapy option by FOne after standard of care diagnostics. Therapeutic alterations were observed particularly in patients with a rare or unknown tumor type.

Successful implementation of genomically based treatment of chemotherapy refractory peripheral T-cell lymphoma (PTCL)

ABSTRACT Background: The treatment of peripheral T-cell lymphoma (PTCL) after failure of standard therapy represents a significant clinical challenge as the best approach has not been defined. The outcomes of patients with peripheral T-cell lymphoma (PTCL) after relapse, in the absence of hematopoietic stem-cell transplantation, are poor with median overall survival is less than six months. Thus, relapsed/refractory PTCL presents an area of unmet medical need. Case presentation: Herein, we report an 84-year old woman with stage IV PTCL with extensive involvement of the bowel and abdominal pain. She was treated with cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) chemotherapy which was complicated by prolonged pancytopenia, without response. Disease progression was manifested by small bowel obstruction, for which she received palliative radiation therapy, further complicated by cardiac arrhythmia and sepsis. In the meantime, clinical-grade next generation sequencing of a lymph node (406 gene panel) showed six genomic alterations: NRAS Q61R, PTEN Q17*, CREBBP R768*, EP300 R1529*, SETD2 loss exons 19–21, along with an intermediate tumor mutational burden. Tissue PD-L1 staining was low positive by immunohistochemistry. The patient was discussed in Molecular Tumor Board with consensus opinion favoring a combination of the MEK inhibitor trametinib (for the NRAS alteration) and the checkpoint inhibitor nivolumab for the elevated mutational burden and PD-L1 positivity. Her abdominal pain resolved and she achieved a complete remission ongoing at 5+ months. Side effects at five months included only low-grade rash and peripheral edema. Conclusions: Our observations suggest that matching patients with hematologic malignancies with customized combinations based on genomic sequencing warrants further study as a way to achieve and/or deepen responses, including in patients who are elderly and/or have refractory disease and significant disease-related complications.

Abstract 4003: Comprehensive genomic profiling of Merkel cell carcinoma samples reveals bimodal distribution of tumor mutational burden and two mutually exclusive candidate mechanisms of malignant transformation

Abstract Merkel cell carcinoma (MCC) is a rare but aggressive skin cancer. Etiologic risk factors include long-term UV exposure, Merkel cell polyomavirus (MCV) infection, age, and immunosuppression. Large-scale investigations of MCC are hindered by its rarity and comprehensive understanding of this disease is currently lacking. In a study of 275 patients, representing the largest sequenced cohort of MCC samples to date, we sought to characterize the genomic landscape of MCC as well as identify whether causality could be attributed to MCV infection, UV exposure, or a synergistic effect between the two. Comprehensive genomic profiling of 395 cancer-related genes, including evaluation of tumor mutational burden (TMB) and mutational signatures, was performed on MCC tumors from 275 patients. The TMB of MCC exhibited a stark bimodal distribution between TMB high (≥20 mutations/mb) and TMB low (&amp;lt;6 mutations/mb) specimens with only 22 specimens having an intermediate TMB. Overall, 101/275 (37%) of MCC samples were TMB high (median 53.1 mutations/mb) with the majority carrying short variant mutations in TP53, RB1, or NOTCH1. Analysis of mutational signatures found that 94/101 (93%) of TMB high samples exhibited signs of UV damage. No signatures indicative of APOBEC activity or of intrinsic DNA repair defects such as microsatellite instability were observed in the TMB high group. In contrast, 152/275 (55%) of MCC specimens were TMB low (median 1.2 mutations/mb) with 39% of these samples having no known or likely genomic driver. We hypothesized that the primary driver in the TMB low group was MCV integration and examined MCV infection through de novo assembly of non-human sequencing reads in all specimens of the MCC cohort. We found 99/152 (65%) of TMB low specimens to be positive for MCV integration as opposed to 0/101 (0%) of TMB high specimens, which was a statistically significant difference (P = 2.20e-31, Fisher's exact test). Overall, 3 of the 22 TMB intermediate specimens were MCV-positive. In a large cohort of 275 patient samples, we have described two genomically distinct subsets of MCC: a TMB high group defined by UV damage with mutations in well-known tumor suppressors and a TMB low group defined by MCV integration. We propose that MCV integration is the dominant driver in the TMB low cohort. Indeed, most MCV sequences that we observed appear to be derived from the large or small T antigens, two established viral oncogenes. These results are suggestive of two distinct etiologies of MCC that appear to be mutually exclusive, namely UV exposure vs. MCV integration. These etiologies may have significant impact on targeted and immuno-therapy options for MCC patients. Citation Format: Meagan Montesion, Ethan S. Sokol, Todd C. Knepper, Andrew S. Brohl, Garrett M. Frampton, Phil J. Stephens, James A. DeCaprio, Kenneth Y. Tsai, Lee A. Albacker. Comprehensive genomic profiling of Merkel cell carcinoma samples reveals bimodal distribution of tumor mutational burden and two mutually exclusive candidate mechanisms of malignant transformation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4003.

Prevalence of PDL1 Amplification and Preliminary Response to Immune Checkpoint Blockade in Solid Tumors

Copy number alterations in programmed cell death ligand 1 (PDL1 or CD274), programmed cell death 1 ligand 2 (PDCD1LG2 or PDL2), and Janus kinase 2 (JAK2) genes (chromosome 9p24.1) characterize Hodgkin lymphoma, resulting in high response rates to programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) blockade. The prevalence and utility of PDL1 amplification as a response biomarker to PD-1/PD-L1 blockade are unknown in other tumors. To examine the prevalence of PDL1 amplification and its utility as a response biomarker to PD-1/PD-L1 blockade in solid tumors. This retrospective study (October 1, 2012, to October 1, 2017) used a deidentified tumor database from a commercial company and annotated clinical records from a subset of patients treated at a university tertiary referral center. The study analyzed 118 187 tumors from the deidentified database, including a clinically annotated subgroup of 2039 malignant tumors. Comprehensive genomic profiling was performed on all samples to determine PDL1 amplification, microsatellite instability, and tumor mutational burden (TMB). A subset of patients was treated with PD-1/PD-L1 blockade. The prevalence of PDL1 amplification was determined among 118 187 patient samples that underwent next-generation sequencing. Solid tumors treated with checkpoint blockade were evaluated for response and progression-free survival (PFS). Of the 118 187 deidentified tumor samples, PDL1 amplifications were identified in 843 (0.7%), including more than 100 types of solid tumors. Most PDL1-amplified tumors (84.8%) had a low to intermediate TMB. PDL1 amplification did not always correlate with high-positive PD-L1 expression by immunohistochemical analysis. Six of 9 patients (66.7%) from 1 center with PDL1-amplified solid tumors had objective responses after checkpoint blockade administration. The median PFS among all treated patients was 15.2 months. Responders included 1 patient with glioblastoma (PFS, ≥5.2 months), 2 patients with head and neck squamous cell cancer (PFS, ≥9 and 15.2 months), 2 patients with metastatic basal cell cancer (PFS, 3.8 and ≥24.1 months), and 1 patient with urothelial cancer (PFS, ≥17.8 months). The results of this study suggest that PDL1 amplification occurs in a small subset of malignant tumors. Additional large-scale, prospective studies of PDL1-amplified cancers are warranted to confirm the responses to checkpoint blockade described herein, even in the absence of microsatellite instability, high PD-L1 expression, and a high TMB.

Tumor Mutational Burden as an Independent Predictor of Response to Immunotherapy in Diverse Cancers.

Immunotherapy induces durable responses in a subset of patients with cancer. High tumor mutational burden (TMB) may be a response biomarker for PD-1/PD-L1 blockade in tumors such as melanoma and non-small cell lung cancer (NSCLC). Our aim was to examine the relationship between TMB and outcome in diverse cancers treated with various immunotherapies. We reviewed data on 1,638 patients who had undergone comprehensive genomic profiling and had TMB assessment. Immunotherapy-treated patients (N = 151) were analyzed for response rate (RR), progression-free survival (PFS), and overall survival (OS). Higher TMB was independently associated with better outcome parameters (multivariable analysis). The RR for patients with high (≥20 mutations/mb) versus low to intermediate TMB was 22/38 (58%) versus 23/113 (20%; P = 0.0001); median PFS, 12.8 months vs. 3.3 months (P ≤ 0.0001); median OS, not reached versus 16.3 months (P = 0.0036). Results were similar when anti-PD-1/PD-L1 monotherapy was analyzed (N = 102 patients), with a linear correlation between higher TMB and favorable outcome parameters; the median TMB for responders versus nonresponders treated with anti-PD-1/PD-L1 monotherapy was 18.0 versus 5.0 mutations/mb (P < 0.0001). Interestingly, anti-CTLA4/anti-PD-1/PD-L1 combinations versus anti-PD-1/PD-L1 monotherapy was selected as a factor independent of TMB for predicting better RR (77% vs. 21%; P = 0.004) and PFS (P = 0.024). Higher TMB predicts favorable outcome to PD-1/PD-L1 blockade across diverse tumors. Benefit from dual checkpoint blockade did not show a similarly strong dependence on TMB. Mol Cancer Ther; 16(11); 2598-608. ©2017 AACR.

Abstract 665: Molecular and clinical analyses of patients with gynecologic malignancies treated with PD-1 directed immunotherapy

Abstract Long term responses are seldom seen in treatments of advanced or recurrent gynecologic cancers. In contrast, immunotherapeutic strategies targeting immune checkpoints such as programmed cell death-1 (PD-1) are currently in active development in platinum resistant gynecologic malignancies with promising durable responses observed in subset of patients. We analyzed all 14 patients with gynecology malignancies that were treated with PD-1 directed immunotherapy, nivolumab or pembrolizumab at the developmental therapeutics program (DTP) clinic in Northwestern University during 2015 till 2016. Seven patients had ovarian/fallopian/peritoneal cancer; six, endometrial cancer; 1, squamous cell carcinoma (SCC) of cervix that are refractory to standard-of-care chemotherapies. Comprehensive genomic profiling including microsatellite instability (MSI) status and tumor mutational burden (TMB) analyses was performed using next generation sequencing (NGS) (FoundationOne). Among 7 patients with ovarian/fallopian/peritoneal cancer (median age, 62 years), objective response rate (ORR) was 20%. One patient had partial response (PR), another one had stable disease (SD), and 3, progressive disease (PD). Two patients were uable to be evaluated. In a patient with PR, CA 125 level normalized from 426.2 to 10.8 U/mL. Her tumor had very low TMB (1/Mbp). In all patients, TMB level varied from very low to low (1-5 mut/Mbp) with MSI status being stable. Progression free survival (PFS) ranged from 14 to 196 days; overall survival (OS) varied from 60 to 199 days. Among 6 patients with endometrial cancer (median age, 68 years), ORR was 20%. One patient had PR while four experienced PD. One patient whose disease could not be assessed due to early death from an event unrelated to treatment had a remarkable chemical response with a decrease in CA125 level from 5,889 to 182.1 U/mL after one single dose. Her tumor had MSI-stable status and intermediate TMB (6 mut/Mbp). In a patient with PR, CA125 level decreased from 1,216 to 226.5 U/mL. Her tumor had MSI-high status with unknown TMB. Of note, one of four patients with PD had MSI-high status and intermediate level of TMB. Other patients had tumor with MSI-stable status and low level of TMB (3-4 mut/MB). PFS ranged from 23 to 258 days; OS varied from 73 to 265 days. One patient with HPV positive SCC of cervix (34 year old) experienced PD. Her tumor had MSI-stable status with unknown TMB. PFS was 88 days; OS, 132 days. In summary, patients with ovarian and endometrial cancer treated with PD-1 directed immunotherapy demonstrated ORR of 20%. One additional patient with endometrial cancer had an exceptional chemical response. None of the tumors had high TMB (&amp;gt;6/Mbp). No clear associations between genomic traits including TMB and MSI staus and responses were found. Further larger prospecitve studies are warranted to explore potential biomarkers for response with immunotherapy in gynecologic malignancies. Note: This abstract was not presented at the meeting. Citation Format: Young Kwang Chae, Sabina Murshudova, William H. Bae, Jonathan F. Anker, Mario J. Pineda, Wilberto Nieves-Neira, Daniela E. Matei, John R. Lurain, Shohreh Shahabi, Francis J. Giles. Molecular and clinical analyses of patients with gynecologic malignancies treated with PD-1 directed immunotherapy [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 665. doi:10.1158/1538-7445.AM2017-665

Comprehensive genomic profiling to identify tumor mutational burden (TMB) as an independent predictor of response to immunotherapy in diverse cancers.

e14508 Background: Immunotherapy induces durable responses in a subset of patients with cancer. High TMB may be a response biomarker for PD-1/PD-L1 blockade in tumors such as melanoma and non-small cell lung cancer (NSCLC). Our aim was to examine the relationship between TMB and outcome in diverse cancers treated with various immunotherapies. Methods: We reviewed data on 1,638 patients who had undergone comprehensive genomic profiling and had TMB assessment. Immunotherapy-treated patients (N = 151) were analyzed for response rate (RR), progression-free and overall survival (PFS, OS). Results: Higher TMB was independently associated with better outcome parameters (multivariable analysis). The RR for patients with high (≥ 20 mutations/mb) vs. low to intermediate TMB was 22/38 (58%) vs. 23/113 (20%) (P = 0.0001); median PFS, 12.8 vs. 3.3 months (P = &lt;0.0001); median OS, not reached vs. 16.3 months (P = 0.0036) (Table). Results were similar when anti-PD-1/PD-L1 monotherapy was analyzed (N = 102 patients), with a linear correlation between higher TMB and favorable outcome parameters; the median TMB for responders vs. non-responders treated with anti-PD-1/PD-L1 monotherapy was 18.0 vs. 5.0 mutations/mb (P &lt; 0.0001). Comparable data was observed when patients with melanoma (N = 52) and NSCLC (N = 36) were excluded (N = 63 patients; 19 tumor types). Interestingly, anti-CTLA4/anti-PD-1 combinations vs. anti-PD-1/PD-L1 monotherapy was selected as a factor independent of TMB for predicting better RR (77% vs. 21%) (P = 0.004) and PFS (P = 0.024). Conclusions: Higher TMB predicts favorable outcome to PD-1/PD-L1 blockade across diverse tumors. Benefit from dual checkpoint blockade did not show a similarly strong dependence on TMB. [Table: see text]

Tumor mutational burden of microsatellite stable metastatic colorectal tumors by patient factors and KRAS, BRAF, and PIK3CA mutation status.

627 Background: Microsatellite instability (MSI) can predict response to pembrolizumab in metastatic colorectal cancer (mCRC). Benefit to PD-1 blockade is limited in microsatellite stable (MSS) mCRC yet MSS tumors represent &gt;95% of all mCRC cases. Evidence suggests that high mutational load remains an important predictor of benefit to checkpoint inhibition across several tumors. We aimed to explore associations between tumor mutational burden (TMB) and various patient factors and mutations of interest to identify features of patients (pts) with MSS mCRC of potential significance to prognosis and PD-1 targeting. Methods: We conducted a retrospective study based on next-generation sequencing (NGS) of MSS metastatic colorectal tumors at our single institution using FoundationOne. TMB was categorized as high ≥ 20 mutations/megabase (Mb), intermediate 6-19 mutations/Mb, and low ≤ 5 mutations/Mb. TMB frequencies were analyzed according to age (≤50, &gt;50, &gt;65, and &gt;70 years old), gender, race, location of primary tumor, and KRAS, BRAF, and PIK3CA mutations. Results: Among 194 MSS tumors with available TMB data, frequencies of tumors with intermediate TMB were significantly different in pts ≤50 years (24.6%, n=69) than in pts &gt;65 (48.9%, n=47, Fisher’s exact (two-tailed) p=0.0096) and &gt;70 (53.1%, n=32, p=0.0067). Frequencies of tumors with low TMB were significantly different in pts ≤50 years (75.4%, n=69) than in pts &gt;65 (46.8%, n=47, p=0.0029) and &gt;70 (43.8%, n=32, p=0.0032). Frequencies of high TMB tumors by age were 0% (≤50 years), 1.6% (&gt;50), 4.3% (&gt;65), and 3.1% (&gt;70) and did not reach significance. Frequencies of high, intermediate, or low TMB tumors were not significantly different based on gender, race, and location of primary tumor. Frequencies of KRAS, BRAF, and PIK3CA mutations were similar across all TMB categories (p=0.7995, 0.8774, and 0.053, respectively). Conclusions: Older individuals with mCRC are less likely to have a low mutation burden by FoundationOne assay. Further validation of these findings in larger cohorts may indicate a potential higher likelihood for elderly colorectal cancer patients to benefit from immune-based strategies.