Median Tumor Mutational Burden Research Articles

Liver metastases and peritoneal metastases and response to checkpoint inhibitors in metastatic colorectal cancer with microsatellite instability.

There have been conflicting reports on the predictive impact of metastatic disease sites on the response to checkpoint inhibitors (CPI) in microsatellite instability (MSI) metastatic colorectal cancers (mCRC). Recent studies have highlighted peritoneal metastases, ascites, and liver metastases as possible indicators of resistance to CPI. We performed a detailed analysis of high microsatellite instability (MSI-H) mCRC treated with programmed cell death (PD-1) or PD-1/cytotoxic T-lymphocyte-associated protein 4 CPI in a single center. Overall response rate (ORR), progression-free survival (PFS), overall survival (OS), and stable disease but with complete pathological response upon resection (SDcPR) were analyzed by the presence of liver metastases, peritoneal metastases, or absence of either. The impact of number and size of liver metastases on clinical outcomes were also interrogated. Thirty-five patients with MSI mCRC were included in the analysis. Patients with peritoneal metastatic disease had lower ORR and shorter PFS compared to patients without liver and peritoneal metastases. Contrary to recent reports, ORR and ORR + SDcPR rates were high in patients with liver metastases, at 58% and 66%, respectively. In the liver metastases category, a better response rate was noted for patients with<5 lesions compared to patients with more than 5 lesions. Patients who responded had a higher median tumor mutation burden than patients with progressive disease. In MSI mCRC, no single clinical characteristic was sufficient to preclude CPI response. Peritoneal metastatic disease was associated with numerically lower ORR and shorter PFS. In contrast, liver metastases do not predict poor outcome.

Genomic landscape of cutaneous, acral, mucosal, and uveal melanoma in Japan: analysis of clinical comprehensive genomic profiling data.

Cutaneous melanoma (CM) is the most common type in Caucasians, while acral melanoma (AM) and mucosal melanoma (MM), which are resistant to immunotherapies and BRAF/MEK-targeted therapies, are more common in East Asians. Genomic profiling is essential for treating melanomas, but such data are lacking in Japan. Comprehensive genomic profiling data compiled in the Center for Cancer Genomics and Advanced Therapeutics (C-CAT) were analyzed. A total of 380 melanomas was analyzed, including 136 CM, 46 AM, 168 MM, and 30 uveal melanoma (UM). MM included conjunctival, sinonasal, oral, esophageal, anorectal, and vulvovaginal melanomas. No significant difference in the median tumor mutational burden (TMB) of CM (3.39 mutations/megabase), AM (2.76), and MM (3.78) was the key finding. Microsatellite instability-high status was found in one case. BRAF V600E/K was found in only 45 patients (12%). Key driver mutations in CM were BRAF (38%), NRAS (21%), NF1 (8%), and KIT (10%), with frequent copy number alterations (CNAs) of CDKN2A, CDKN2B, and MYC. AM was characterized by altered KIT (30%), NRAS (26%), and NF1 (11%) and CDKN2A, CDKN2B, CDK4, MDM2, and CCND1 CNAs. MM was characterized by altered NRAS (24%), KIT (21%), and NF1 (17%) and MYC, KIT, and CDKN2A CNAs, with differences based on anatomical locations. UM bore GNAQ or GNA11 driver mutations (87%) and frequent mutations in SF3B1 or BAP1. The distinct genomic profiling in Japanese patients, including lower TMB, compared to Caucasians, is associated with poorer treatment outcomes. This result underscores the need for more effective therapeutic agents.

Liquid-liquid phase separation-related signature predicts prognosis and therapeutic response in esophageal adenocarcinoma

BackgroundEsophageal adenocarcinoma is a leading cause of mortality worldwide. New evidence indicates that liquid-liquid phase separation is related to malignancies. The current study aims at exploring the functions of liquid-liquid phase separation within esophageal adenocarcinoma. Patients within the TCGA dataset were classified using liquid–liquid phase separation-related genes. Significantly differentially expressed genes and prognostic factors for overall survival have been screened by Cox regression. Based on the liquid-liquid phase separation score, the construction of a prognostic model and liquid-liquid phase separation signature was constructed. Tumor mutation burden and drug sensitivity were analyzed in two groups: high liquid-liquid phase separation scores, and low liquid-liquid phase separation scores. According to liquid-liquid phase separation, some small-molecule compounds targeting esophageal adenocarcinoma were screened. The results were verified in vitro with an external cohort. Results87 samples are involved, and 61 liquid-liquid phase separation-related genes may influence esophageal adenocarcinoma by changing DNA conformation and metabolism. Meanwhile, based on a high liquid-liquid phase separation score and low score group including 43 patients, it is found that the result significantly lowered the 5-year overall survival to 32.6 %, compared to 64.8 % in the low-score group of 44 patients with p < 0.001. The high score group had an average TIDE score of 0.27 versus 0.14 in the low-score group, with p = 0.003. The median tumor mutation burden was 9.1 mutations/Mb in the high-score group versus 6.4 mutations/Mb in the low-score group, with p = 0.011. The predictive model worked very well, with area under the curve values of 0.82, 0.79, and 0.76 for 1-, 3-, and 5-year survival, respectively. Liquid-liquid phase separation has been validated as an effective prognostic biomarker and drug sensitivity predictor. SignificanceLiquid-liquid phase separation is potentially implicated in esophageal adenocarcinoma and works as a prognostic biomarker assessment of vulnerability to LLPS, which could help develop individualized therapies by showing how one is situated about various medications where responses vary across the body.

Genomic landscape of malignant phyllodes tumors reveals multiple targetable opportunities.

Malignant phyllodes tumors (MPT) are rare fibroepithelial breast cancers with no known effective systemic therapy; metastatic progression portends a dismal prognosis. We sought to describe the genomic landscape of MPTs through genomic profiling and immunotherapeutic biomarker analysis. Cases of sequenced MPT were identified from a Clinical Laboratory Improvement Amendments-certified, College of American Pathologists-accredited laboratory (Foundation Medicine). All cases underwent genomic profiling using adaptor ligation-based, next-generation sequencing assay of 324 genes. Tumor agnostic immunotherapy biomarkers, microsatellite instability, tumor mutational burden (TMB), and programmed death-ligand 1 (PD-L1) expression were evaluated. Fisher's Exact Tests and analysis of variance were used to test for differences between groups and for continuous variables as appropriate. Of 135 MPT cases identified; 94 (69.6%) were localized/locally recurrent and 41 (30.4%) were metastatic. Median age was 54 years (range 14-86). The median TMB was 2.5 mut/Mb and 3 were TMB-high (≥10 mut/Mb). 21.4% were PD-L1+ via Dako 22C3 assay (CPS ≥1). Most commonly altered genes included TERT-promoter (69.7%), CDKN2A (45.9%), TP53 (37.8%), NF1 (35.6%), CDKN2B (33.3%), MED12 (28.9%), MTAP (27.7%), KMT2D (22.2%), PIK3CA (20.0%), PTEN (18.5%), and RB1 (18.5%). Several tumors harboring genomic alterations with US Food and Drug Administration-approved indications in other tumor types were found including NF1, PIK3CA, EGFR Exon 19/20 insertions, and BRAF V600E mutations. In the largest genomic evaluation of MPT to date, multiple clinically actionable mutations were found. Routine sequencing of metastatic MPT may provide additional information to guide treatment decisions and clinical trial enrollment.

Bruton's tyrosine kinase inhibitor zanubrutinib-based regimens in relapsed/refractory primary diffuse large B-cell lymphoma of central nervous system.

30 Background: Patients with relapsed/refractory primary central nervous system lymphoma (R/R PCNSL) usually have a poor prognosis. Ibrutinib-based regimens revealed promising efficacy but showed off-target effects and drug resistance in some cases. Here, we conducted a retrospective study to evaluate the efficacy and safety of regimens based on second-generation bruton's tyrosine kinase (BTK) inhibitor zanubrutinib in R/R PCNSL. Methods: We respectively reviewed 23 patients with R/R PCNSL treated with zanubrutinib in our center from Apr. 2021 to Jan. 2024. The primary end points were overall response rate (ORR) and progression-free survival (PFS). Secondary end points included complete response rate (CRR), disease control rate (DCR), overall survival (OS) and adverse events (AEs). Response was assessed according to International Primary CNS Lymphoma Collaborative Group criteria. The severity of AEs was graded using the NCI Common Toxicity Criteria, version 5.0. Validated next-generation sequencing (NGS) panels were used to analyze the mutational status of the BCR pathway genes or other solid tumor-related genes. Results: The median follow-up at the cutoff date (15 Jan 2024) was 17.0 months (range, 2-33 months). The ORR, CRR and DCR were 78.3%, 39.1% and 91.3%. The median PFS was 31.0 months, but the median OS was not reached. Compared to germinal center B-cell like (GCB) group, non-GCB group showed a better ORR (76.9% vs 66.7%) and CRR (46.2% VS 33.3%). Multivariate analysis revealed that overall response (vs. no response, HR=0.20, P=0.027), long duration of zanubrutinib (≥6months vs. 2-5 months, HR=0.07, P=0.009) and refractory disease status (vs. relapse disease status, HR=0.12, P=0.014) were independent factors for longer PFS. The most commonly mutated genes are MYD88(15/17,88.2%), PIM1(9/17 52.9%), CD79B (8/17,47.1%), ETV6(7/17,41.2%), BTG1(5/17,29.4%) and GNA13(5/17,29.41%). The mutational status of MYD88/CD79B did not lead to any difference in PFS and OS. We obtained the Tumor Mutational Burden (TMB) information from 11 patients. The median TMB was 15.96 (range: 3.82-28.11) muts/Mb. Kaplan-Meier analysis demonstrated that PFS was significantly longer in patients with higher TMB (≥15.96 muts/Mb) after zanubrutinib-based treatment(P=0.005). Grade ≥3 and serious treatment-emergent AEs (TEAEs) were not found. The most commonly TEAEs were hematologic toxicity (8/23,34.8%) and skin rash (5/23,21.7%). Conclusions: Our study demonstrates that zanubrutinib-based therapy is effective and safe for the treatment of R/R PCNSL. We advocate for the prolonged administration of zanubrutinib to maintain treatment response. Patients with higher TMB derive greater benefits from zanubrutinib-based regimens.

Effect of heterozygosity loss of HLA-I on immune evasion and promotion of non-small cell lung cancer brain metastasis and immunotherapy resistance.

209 Background: HLA-I play a crucial role in T cell recognition and killing of tumor cells as well as in PD-1/PD-L1 immunotherapy. Loss of heterozygosity (LOH) of HLA-I alleles has been found to be common in lung cancer patients and influences immune escape during tumor evolution. This study aims to explore the incidence of HLA-I LOH in intracranial metastases of advanced non-small cell lung cancer patients with brain metastasis and its impact on the efficacy of immunotherapy. Methods: A total of 29 patients with non-small cell lung cancer brain metastasis were included in this study. All enrolled patients underwent either percutaneous biopsy or surgical resection of intracranial metastases and had tissue specimens from the primary lung lesions. Whole-exome sequencing was performed on all primary/metastatic lesions to determine HLA-I typing/LOH and calculate tumor mutation burden (TMB). Additionally, we assessed the expression levels of CD8 T cells in the tumor immune microenvironment. Among the enrolled patients, 20 received PD-1/PD-L1 treatment. Results: Among the enrolled patients, 82.8% (24/29) had heterozygous HLA-I typing, with HLA-I LOH present in 25% (6/24) of patients' primary lesions and 58.3% (14/24) in brain metastatic lesions. Analysis of TMB in different lesions revealed a median TMB of 7.8 mut/Mb in lesions with intact HLA-I and 11.4 mut/Mb in lesions with HLA-I LOH. Notably, the median TMB in brain metastatic lesions with HLA-I LOH was 13.2 mut/Mb, higher than that in HLA-I LOH primary lung lesions (10.1 mut/Mb). Immunohistochemistry demonstrated that CD8 T cell expression levels were lowest in brain metastatic lesions with HLA-I LOH and highest in intact HLA-I primary lung lesions. Among patients who received immunotherapy, four cases exhibited inconsistent lesion responses, with stable or regressing primary lesions but progressive intracranial metastases. Survival analysis revealed that patients with HLA-I LOH in brain metastases had significantly lower PFS compared to those without (4.1 months vs. 6.9 months, P &lt; 0.05), with no significant difference in OS. Conclusions: This study indicates that the incidence of HLA-I LOH in brain metastases of lung cancer is higher than that in primary lung lesions, accompanied by higher TMB, possibly due to the ineffective presentation of tumor antigens resulting in the accumulation of mutations in lost HLA-I. Moreover, tumors with HLA-I LOH have reduced levels of CD8 T cell infiltration, suggesting impaired tumor antigen presentation impedes immune cytotoxicity. These phenomena contribute to the poorer efficacy of immunotherapy in such patients. In conclusion, HLA-I LOH may be one of the important mechanisms of immune escape in lung cancer brain metastases.

Urachal and Nonurachal Adenocarcinomas of the Urinary Bladder: A Comprehensive Genomic Profiling Study.

Although both urachal (U) and nonurachal (NU) bladder adenocarcinomas (adenoCas) share several histologic similarities, they differ in location and sometimes in therapeutic options. We analyzed the differences in genomic alterations (GAs) between these tumor entities, with the aim of identifying potential therapeutic targets for clinical trials. Overall, 133 U and 328 NU adenoCas were analyzed. Hybrid capture-based comprehensive genomic profiling (CGP) was performed to evaluate all classes of GA. Germline status of GA was predicted using a validated somatic-germline computational method. CGP was performed using the FoundationOne and FoundationOne CDx assays (Foundation Medicine, Inc). The most frequent GA in both U and NU cohorts included TP53 (86.5% v 81.1%) and KRAS (34.6% v 27.7%). GAs characteristic of colorectal adenoCa, such as SMAD4 (P = .069) and GNAS (P = .071), were more common in U versus NU. Conversely, TERT (P < .01) and RB1 (P = .071) were more prevalent in NU adenoCa. Notably, both U and NU adenoCas exhibited possibly targetable GA in PIK3CA (7.5% v 7.9%) and ERBB2 (6.8% v 7.6%). Biomarkers associated with potential benefit from anti-PD-1/L1 were infrequent. Median tumor mutational burden was 2.6 and 3.5 mutations per megabase for U and NU, respectively, and PD-L1 expression >1% was rare. Genomic ancestry and genomic signature distribution were similar in both tumor types. GAs were most commonly of somatic nature. Limitations include lack of clinical data, tumor heterogeneity, and retrospective nature. U and NU adenoCAs revealed differences in GA, with PIK3CA and ERBB2 being identified as putative therapeutic targets. Biomarkers of response to anti-PD-(L)1 were uncommon. Results highlight the potential of CGP to personalize treatment options of bladder adenoCa and inform clinical trial designs.

Tissue- and liquid-biopsy based NGS profiling in advanced non-small-cell lung cancer in a real-world setting: the IMMINENT study.

To date, for all non-small cell lung cancer (NSCLC) cases, it is recommended to test for driver alterations to identify actionable therapeutic targets. In this light, comprehensive genomic profiling (CGP) with next generation sequencing (NGS) has progressively gained increasing importance in clinical practice. Here, with the aim of assessing the distribution and the real-world frequency of gene alterations and their correlation with patient characteristics, we present the outcomes obtained using FoundationOne (F1CDx) and FoundationLiquid CDx (F1L/F1LCDx) NGS-based profiling in a nationwide initiative for advanced NSCLC patients. F1CDx (324 genes) was used for tissue samples, and F1L (70 genes) or F1LCDx (324 genes) for liquid biopsy, aiming to explore the real-world occurrence of molecular alterations in aNSCLC and their relationship with patients' characteristics. Overall, 232 advanced NSCLC patients from 11 Institutions were gathered [median age 63 years; never/former or current smokers 29.3/65.9%; adenocarcinoma/squamous 79.3/12.5%; F1CDx/F1L+F1LCDx 59.5/40.5%]. Alterations were found in 170 different genes. Median number of mutated genes per sample was 4 (IQR 3-6) and 2 (IQR 1-3) in the F1CDx and F1L/F1LCDx cohorts, respectively. TP53 (58%), KRAS (22%), CDKN2A/B (19%), and STK11 (17%) alterations were the most frequently detected. Actionability rates (tier I and II) were comparable: 36.2% F1CDx vs. 34% ctDNA NGS assays (29.5% and 40.9% F1L and F1LCDx, respectively). Alterations in KEAP1 were significantly associated with STK11 and KRAS, so as TP53 with RB1. Median tumor mutational burden was 6 (IQR 3-10) and was significantly higher in smokers. Median OS from metastatic diagnosis was 23 months (IQR 18.5-19.5) and significantly lower in patients harboring ≥3 gene mutations. Conditional three-year survival probabilities increased over time for patients profiled at initial diagnosis and exceeded those of individuals tested later in their clinical history after 12 months. This study confirms that NGS-based molecular profiling of aNSCLC on tissue or blood samples offers valuable predictive and prognostic insights.

Tumor mutation burden and FAT3 mutation influence long-term survival in surgically resected small cell lung cancer.

Small cell lung cancer (SCLC) is highly malignant and has a higher risk of recurrence even in patients who undergo early surgery. However, a subgroup of patients survived for many years. So far, the factors that determine the long-term survivorship remain largely unknown. To determine the genetic characteristics of long-term survival (LTS) after surgery in SCLC, we performed comprehensive comparative genomic profiling and tumor mutation burden (TMB) analysis of resected tumor tissues from patients with LTS and short-term survival (STS) after surgery. The present study screened 11 patients from 52 patients with SCLC who underwent surgery at Zhejiang Cancer Hospital from April 2008 to December 2017. A total of six LTS patients (≥4 years) with stage IIB or IIIA SCLC and five STS patients (<2 years) with stage IA or IB SCLC were included in the study. The STS patients were used as a control. All the patients underwent resection without neoadjuvant therapy. We assessed the genomic profiles of the resected tumor tissues and calculated the TMB using next-generation sequencing. We then analyzed and compared the molecular characteristics between the LTS and STS groups. Our data indicated that tumor tissues from patients with LTS harbor a high TMB. The median TMB for LTS patients was high (approximately 16.4 mutations/Mb), while that for STS patients was low (approximately 8.5 mutations/Mb). The median TMB of patients with LTS and STS showed a trend of significant difference (P=0.08). Gene alterations characterized the survival differences between the two groups. The FAT3 mutation was only found in the LTS group, and the P value determined by Fisher's exact test was 0.06. A high non-synonymous TMB and the FAT3 mutation could potentially influence LTS after SCLC resection. This study provides valuable information about the molecular differences between LTS and STS patients. Studies with larger sample sizes need to be conducted to confirm our findings in the future.

On the right TRACK: Providing comprehensive genomic profiling (CGP) and molecular tumor board (MTB) for patients (pts) with rare cancers.

3127 Background: Patients (pts) with rare cancers are under-represented in precision medicine trials despite making up ~22% of cancer incidence. We created the TCF-001 TRACK (Target RAre Cancer Knowledge, NCT04504604) study to provide a home-based, patient-centered trial utilizing comprehensive genomic profiling (CGP) at enrollment and progression with review by a molecular tumor board (MTB). Methods: Pts with rare cancers (incidence&lt;6/100,000) were enrolled and consented remotely (WCG IRB 1287011). Liquid (blood via mobile phlebotomy) and tissue biopsy samples were sent for CGP at Foundation Medicine. A fully remote MTB was convened following availability of each test. MTB notes and therapy recommendations were returned to patients and local physicians. Results: TRACK activated on 1 Oct 2020. The MTB included medical/surgical oncologists, genomics experts, molecular pathologists, a basic scientist, a pharmacist, a genetic counselor, regulatory staff, a scribe, an oncology fellow (“mentern”), and a medication acquisition specialist. MTB members were from 8 states. 132 eligible pts with evaluable results were enrolled from 41 states. Tissue and liquid biopsy results were available in 89 pts; tissue only in 5; liquid only in 38. 128 pts had an MTB before the 30 June2023 cut-off date (mean age 54.1 y; female 61.7%). There were &gt;40 rare/ultra-rare cancers, including cholangiocarcinoma (62) and soft tissue tumors (24). No pts had identical molecular alterations. The median number of pathogenic alterations per tissue sample was 3 (range: 0-14) and blood was 2 (range: 0-40). 3 patients had no pathogenic alterations on tissue or liquid CGP. The most commonly altered genes found by tissue biopsy CGP on study (n=68) were TP53(33.8%), CDKN2A (25.0%), KRAS (23.5%), CDKN2B (17.6%), IDH1 (17.6%), and MTAP (14.7%); by liquid biopsy (n=126), they were TP53 (31.7%), KRAS (11.9%), and IDH1 (8.7%), as well as genes often associated with clonal hematopoiesis: DNMT3A (22.2%), ATM (12.7%), and CHEK2 (8.7%). The sensitivity of liquid biopsy for pathogenic alterations found in tissue was 89.3% for pts with ctDNA tumor fraction (TF) ≥1% and 28.1% for TF &lt;1%. 1 pt had microsatellite instability. Median tumor mutational burden (TMB) by tissue was 2.5 mutations/megabase and by blood was 1.3. 3 pts had TMB≥10. Liquid biopsy results were available more quickly than tissue (median processing time, 9.1 vs 13.3 days); time from submission to processing was shorter for blood than tissue (2.4 vs 4.9 weeks). TRACK staff encountered 0.94 queries/sample. MTB recommendations based on CGP were generated for 87.5% of the 128 pts presented. Conclusions: A fully remote, advocacy driven, national precision genomics trial is feasible for managing rare cancers. CGP with expert MTB review can identify potentially targetable alterations and inform therapeutic options. Clinical trial information: NCT04504604 .

Prognostication of ß-catenin (CTNNB1) in patients with HCC treated with first line immunotherapy.

e15146 Background: Wnt/ß-catenin signaling dysregulation is found in approximately 25% of hepatocellular carcinoma (HCC) patients. The impact of B-catenin activation on HCC overall survival has remained controversial. Prior studies suggest activating CTNNB1 mutations may predict for immunotherapy (IO) resistance while others did not corroborate this finding. Here we describe the clinical outcomes of advanced HCC patients (pts) with CTNNB1 (+) and without CTNNB1 (-) mutations treated with novel first line IO/anti-VEGF therapies. Methods: We conducted a multicenter, retrospective analysis of pts with HCC who had molecular analysis performed between 2019 and 2023 at Mayo Clinic in Minnesota, Arizona, and Florida. The study was reviewed and approved by the IRB. Clinical and molecular features were compared descriptively. The primary outcomes were time to treatment failure (TTF), defined as time from first-line treatment initiation to off treatment or death, and overall survival (OS), defined as time from first-line treatment initiation to death, compared between the two cohorts using the Kaplan-Meier method. Results: We identified 29 CTNNB1+ and 62 CTNNB1- (wt) pts with HCC. Median age at diagnosis was 66 (range 30-86), 80 (88%) were Caucasian, 68 (75%) were male gender, and 22 (24%) had etiology as hepatitis B/hepatitis C, 82 (90%) were Child-Pugh A and 77 (85%) were Barcelona Clinic Liver Clinic (BCLC)=C at diagnosis. Eighteen (90%, n=20) CTNNB 1+ pts received first-line IO (Atezolizumab/bevacizumab [AB]) vs 39 (72%, n=54) in CTNNB1- pts. All pts were microsatellite stable (MSS). CTNNB1+ had a similar median tumor mutational burden (TMB), higher rate of TERT co-mutation, and lower rate of TP53 co-mutation (table) compared to CTNNB-. Of 57 AB pts, 5 (27%) of CTNNB1 + had an objective response, compared to 6 (16.7%) CTNNB1- pts. Time to treatment failure with first-line AB and overall survival were similar between the two cohorts (Table). Conclusions: Our study suggests CTNNB1 status is not prognostic in HCC pts receiving IO based therapy. Prospective study is warranted to further investigate predictive biomarkers for HCC sensitivity to immune checkpoint inhibitors and VEGF-targeted therapy. [Table: see text]

Comprehensive characterization of ERBB2 genomic alterations inlung cancer.

3148 Background: ERBB2mutations () occur in 1-4% of non-small cell lung cancers (NSCLC). Trastuzumab-deruxtecan is FDA-approved for the treatment of metastatic ERBB2-mutant NSCLC based mostly on data from NSCLCs harboring tyrosine kinase domain (TKD) ERBB2mut. The genomic and clinical characteristics of NSCLC with ERBB2 mut beyond the TKD remain largely unexplored. Methods: Patients (pts) with NSCLCs with oncogenic ERBB2 mut and genomic tumor profiling data from the AACR Project GENIE database were included. The cohort was divided into pts with tumors harboring TKD, extracellular (ECD), or transmembrane (TMD) and juxtamembrane domain (JMD) ERBB2mut. Clinico-genomic characteristics were compared between the groups. The Kaplan-Meier method was used to estimate progression-free survival (PFS) with first-line systemic therapy, and log-rank tests were used for comparisons. Results: Of 483 pts with ERBB2-mutant NSCLC, 64% were female, 81% were White, and 13% were Asian. TKD, ECD, and TMD/JMD ERBB2 mut were identified in 362 (75%), 88 (18%), and 33 (7%) cases, respectively. Pts with ECD vs. TKD ERBB2mut tumors were more likely to be males (47% vs. 33%, p=0.03) and have tumors with squamous histology (7% vs. 1%, p&lt;0.0001). Among pts with (n=39), those with ECD vs. TKD ERBB2 mut tumors were more likely to have a history of smoking (100% vs. 42%, p = 0.02). The most common TKD, ECD, and TMD/JMD ERBB2 mut were in-frame ex20ins Y772_A775dup (n=224/362, 62%), missense S310F/Y (n=45/88, 51%), and missense V659E/D (n=10/33, 30%) mut, respectively. ECD vs. TKD ERBB2-mutant tumors harbored a distinct genomic phenotype with significantly higher median tumor mutational burden (11.1 vs. 5.2 mut/Mb, p&lt;0.003), median fraction of genome altered (0.2 vs. 0.1, p = 0.02), and rate of co-mut in EGFR (32% vs. 3.6%, p&lt;0.0001), KRAS (17% vs. 2.5%, p&lt;0.0001), STK11 (23% vs. 4.3%, p&lt;0.0001), KEAP1 (23% vs 5%, p&lt;0.0001) and SMARCA4 (19% vs 4.5%, p&lt;0.0001). Of 343 cases with ERBB2 copy number profiling, 32 (9.3%) harbored ERBB2 amplification. ERBB2-mutant NSCLCs with vs. without ERBB2amplifications had a higher frequency of TP53 co-mut (84% vs. 48%, p &lt;0.001). Of 39 pts with available clinical data, most had ECD (n=6) ERBB2 mut tumors and received first-line platinum-based chemotherapy (n=31). The presence of a co-mut in STK11 (HR 3.5, 0.4–27.4, p=0.03) and KEAP1 (HR 3.9, 0.7–20.6, p=0.002) conferred shorter PFS on first-line systemic therapy. Pts with ECD vs. TKD ERBB2 mut tumors had shorter PFS (HR 2.4, 95% CI 0.7–8.2, p=0.04). Conclusions: NSCLC tumors harboring ECD ERBB2 mut are associated with a distinct clinical and molecular phenotype and inferior outcomes with chemotherapy compared to pts with tumors harboring TKD mut. These findings enhance our understanding of disease heterogeneity in ERBB2-mutant NSCLC and may aid in optimizing treatment strategies for this unique population.

Comprehensive germline and somatic DDR genomic profiles of Chinese patients with multiple primary lung cancer.

e20019 Background: The number of multiple primary lung cancer (MPLC) patients has rapidly increased in recent years. Disruption of the DNA damage repair (DDR) gene is related to cancer risk, progression, and treatment selection. However, the characteristics and significance of DDR alterations remain undefined in MPLC. Methods: A total of 133 Chinese MPLC patients with 308 lesions were enrolled and 784 single-focus lung cancer (SFLC) patients were analyzed as a control in the present study. Genetic testing was performed by utilizing the next-generation sequencing (NGS) of 808 cancer-related genes including 276 DDR genes. The patients were divided into 3 groups: DDR-germline (germline variants, N = 11), DDR-somatic group (somatic variants, N = 98), and the non-DDR group (no DDR variants, N = 24). Results: The overall DDR variants were identified in 82.0% (109/133) of the patients, and a total of 283 variants were found, with almost all being somatic (254/283). The most commonly germline alterations were found in RAD50 (1.5%), WRN (1.5%) and BRCA2 (0.8%), while in the somatic mutations, TP53 (26.3%) showed the highest frequency. DDR-somatic group was more likely to have alterations in TP53, LRP1B, ERBB2 and MYC compared with DDR-germline group. Taken non-DDR group as reference, mutations in TP53 (P&lt;0.05), ALK and PIK3CA were more common in DDR-germline group, but EGFR, RBM10, TP53, LRP1B, TERT and MYC (all P&lt;0.05) in DDR-somatic group. Furthermore, the DDR-somatic group exhibits the highest median tumor mutational burden (6.56) compared with 3.55 (P&lt;0.01) in DDR-germline and 3.69 (P&lt;0.01) in non-DDR group. In addition, the copy number variation (CNV) was statistically different among the three groups (P&lt;0.001). The proportion of copy number gain patients in DDR-somatic group is the highest (28.3%) compared with 12.0% in DDR-germline group and 10.9% in non-DDR group (P&lt;0.01). DDR-somatic MPLC and SFLC patients possessed distinct somatic genomic characteristics, especially with significantly different prevalence in TP53, RBM10, KRAS, BRAF, and ALK (all P&lt;0.05). Moreover, we also found notable differences in the prevalence of TP53 and CNV (both P&lt;0.05) between DDR-germline MPLC and SFLC patients. Conclusions: MPLC patients exhibit a distinctive DDR mutations landscape. The differences in the mutation profile between the DDR-germline and DDR-somatic groups and the distinct actionable genes may indicate the different target-therapy choices for MPLC patients.

Abstract PO5-06-14: Genomic Landscape and Clinical Outcomes of Triple-Negative Invasive Lobular Carcinoma

Abstract Background: Triple-negative (TN) invasive lobular carcinoma (ILC) of the breast is a rare entity, comprising roughly 2% of primary ILC. Clinicopathologic studies have shown that TN ILC is associated with more pleomorphism, higher nuclear grade, older patient age, and worse disease-related outcomes compared to estrogen receptor-positive (ER+) ILC. Intrinsic subtyping indicates that TN ILC less frequently expresses basal markers than TN invasive ductal carcinoma (IDC). This prompted investigation of the genomic landscape and clinical management of TN ILC to provide insight into potential therapeutic approaches. Methods: Twenty patients with TN ILC were included in this study. Three patients were treated at a single academic center and underwent comprehensive genomic profiling (CGP) of breast or metastatic tissue; clinicopathologic details were obtained from their electronic health records. Seventeen patients with TN ILC who underwent CGP of breast or metastatic biopsies were included from the Foundation Medicine, Inc. database. PD-L1 testing for all patients was determined by immunohistochemistry (IHC) using the VENTANA SP142 or Dako 22C3 commercial assays. HER2 expression was determined by IHC. Negative HER2 expression was defined as an IHC score of 0, or IHC 1+ or 2+ with non-amplified fluorescence in situ hybridization (FISH). Results: In the Foundation Medicine database of patients with TN ILC, the most frequent genomic alterations were in CDH1 (15/17 patients [88.2%]), TP53 (10/17 patients [58.8%]), and PIK3CA (10/17 patients [58.8%]). Short variant mutations in ERBB2 were found in 3/17 patients (17.6%). Fourteen patients were HER2-low (HER2 IHC 1+ or 2+ with non-amplified FISH). No cases were MSI high or expressed PD-L1 (8 of 17 cases underwent PD-L1 assessment by SP142). Median tumor mutational burden (TMB) was 5 muts/Mb. Among the three patients with TN ILC treated at a single center, the most common somatic mutations were in CDH1 and TP53, and no cases were MSI high or expressed PD-L1 (by SP142 or 22C3). All three patients had pleomorphic ILC, histologic grade 2 or 3, and HER2 IHC 0. One patient with mpT1cN1a(sn) ER+/HER2- ILC of the right breast in 2011 received adjuvant TAC (docetaxel, doxorubicin, cyclophosphamide), breast/axillary radiation, and ten years of adjuvant endocrine therapy. She was diagnosed with TN ILC of the left supraclavicular nodes in 2022; she did not exhibit a response to docetaxel and carboplatin with pembrolizumab, and she subsequently received palliative radiation followed by capecitabine. Another patient with locally advanced TN ILC progressed on the KEYNOTE-522 regimen, immediately developed metastases, and is currently receiving palliative sacituzumab govitecan. The third patient with cT3N1 TN ILC progressed on neoadjuvant therapy (through the I-SPY 2 trial) with oral paclitaxel, encequidar, and dostarlimab, followed by dostarlimab with dose-dense doxorubicin and cyclophosphamide. Her surgical pathology demonstrated ypT3N3a disease with 10 × 7 cm of tumor, and she developed skin metastases on the chest wall within weeks post-operatively. She received comprehensive chest wall and nodal radiation and is currently receiving palliative capecitabine with neratinib given a high variant allele frequency driver somatic ERBB2 mutation. Conclusions: The most common somatic mutations among TN ILC patients included in this study were in CDH1, TP53, and PIK3CA. Currently the management of TN ILC is extrapolated from that of TN IDC, however our patients did not respond to chemoimmunotherapy. The presence of HER2-low status or somatic ERBB2 mutations may provide opportunities for treatment with an anti-HER2 antibody-drug conjugate or tyrosine kinase inhibitor. Studies with larger sample sizes of TN ILC are needed for molecular profiling and assessment of outcomes with specific therapeutic approaches. Citation Format: Hemali Batra-Sharma, Smruthy Sivakumar, Prashanth Ashok Kumar, Ethan Sokol, Rebecca Shatsky, Jeffrey Ross. Genomic Landscape and Clinical Outcomes of Triple-Negative Invasive Lobular Carcinoma [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-06-14.

Comprehensive genomic profiling of pulmonary spindle cell carcinoma using tissue and plasma samples: insights from a real-world cohort analysis.

Pulmonary spindle cell carcinoma (PSCC) is a rare and aggressive non-small cell lung cancer (NSCLC) subtype with a dismal prognosis. The molecular characteristics of PSCC are largely unknown due to its rarity, which limits the diagnosis and treatment of this historically poorly characterized malignancy. We present comprehensive genomic profiling results of baseline tumor samples from 22 patients histologically diagnosed with PSCC, representing the largest cohort to date. Somatic genetic variant detection was compared between paired plasma samples and primary tumors from 13 patients within our cohort. The associations among genomic features, treatment, and prognosis were also analyzed in representative patient cases. TP53 (54.5%), TERT (36.4%), CDKN2A (27.3%), and MET (22.7%) were most frequently mutated. Notably, 81.8% of patients had actionable targets in their baseline tumors, including MET (22.7%), ERBB2 (13.6%), EGFR (9.1%), KRAS (9.1%), ALK (9.1%), and ROS1 (4.5%). The median tumor mutation burden (TMB) for PSCC tumors was 5.5 mutations per megabase (muts/Mb). TMB-high tumors (>10 muts/Mb) exhibited a significantly higher mutation frequency in genes such as KRAS, ARID2, FOXL2, and LRP1B, as well as within the DNA mismatch repair pathway. The detection rates for single nucleotide variants and structural variants were comparable between matched tumor and plasma samples, with 48.6% of genetic variants being mutually identified in both sample types. Additionally, a patient with a high mutation load and positive PD-L1 expression demonstrated a 7-month survival benefit from chemoimmunotherapy. Furthermore, a patient with an ALK-rearranged tumor achieved a remarkable 3-year progression-free survival following crizotinib treatment. Overall, our findings deepen the understanding of the complex genomic landscape of PSCC, revealing actionable targets amenable to tailored treatment of this poorly characterized malignancy.

Development and validation of an interpretable radiomic signature for preoperative estimation of tumor mutational burden in lung adenocarcinoma.

Tumor mutational burden (TMB) is a promising biomarker for immunotherapy. The challenge of spatial and temporal heterogeneity and high costs weaken its power in clinical routine. The aim of this study is to estimate TMB preoperatively using a volumetric CT-based radiomic signature (rMB). Seventy-one patients with resectable lung adenocarcinoma (LUAD) who underwent whole-exome sequencing (WXS) from 2011 to 2014 were enrolled from the institutional biobank of Tianjin Medical University Cancer Institute and Hospital (TMUCIH). Forty-nine LUAD patients with WXS from the Cancer Genome Atlas Program (TCGA) served as the external validation cohort. Computed tomography (CT) volumes were resampled to 1-mm isotropic, semi-automatically segmented, and manually adjusted by two radiologists. A total of 3,108 radiomic features were extracted via PyRadiomics and then harmonized across cohorts by ComBat. Features with inter-segmentation intra-class correlation coefficient (ICC) > 0.8, low collinearity, and significant univariate power were passed to the least absolute shrinkage and selection operator (LASSO)-logistic classifier to discriminate TMB-high/TMB-low at a threshold of 10mut/Mb. The receiver operating characteristic (ROC) curve analysis and calibration curve were used to determine its efficiency. Shapley values (SHAP) attributed individual predictions to feature contributions. Clinical variables and circulating biomarkers were collected to find potential associations with TMB and rMB. The top frequently mutated genes significantly differed between the Chinese and TCGA cohorts, with a median TMB of 2.20 and 3.46mut/Mb and 15 (21.12%) and 9 (18.37%) cases of TMB-high, respectively. After dimensionality reduction, rMB comprised 21 features, which reached an AUC of 0.895 (sensitivity = 0.867, specificity = 0.875, and accuracy = 0.873) in the discovery cohort and 0.878 (sensitivity = 1.0, specificity = 0.825, and accuracy = 0.857 in a consist cutoff) in the validation cohort. rMB of TMB-high patients was significantly higher than rMB of TMB-low patients in both cohorts (p < 0.01). rMB was well-calibrated in the discovery cohort and validation cohort (p = 0.27 and 0.74, respectively). The square-filtered gray-level concurrence matrix (GLCM) correlation was of significant importance in prediction. The proportion of circulating monocytes and the monocyte-to-lymphocyte ratio were associated with TMB, whereas the circulating neutrophils and lymphocyte percentage, original and derived neutrophil-to-lymphocyte ratio, and platelet-to-lymphocyte ratio were associated with rMB. rMB, an intra-tumor radiomic signature, could predict lung adenocarcinoma patients with higher TMB. Insights from the Shapley values may enhance persuasiveness of the purposed signature for further clinical application. rMB could become a promising tool to triage patients who might benefit from a next-generation sequencing test.

Targeted DNA Sequencing Reveals Molecular Factors Associated with Clinical Outcomes in Recurrent Glioblastoma

INTRODUCTION: The prognostic significance of molecular alterations in recurrent glioblastoma (rGBM) remains unclear. METHODS: 121 consecutive glioblastoma (GBM) patients who underwent re-resection at a single institution from 2016-2021 were retrospectively reviewed. All patients underwent maximal safe resection followed by radiotherapy with concurrent and adjuvant temozolomide (TMZ) at time of initial diagnosis. DNA mutations from re-resection samples were assessed with a CLIA certified next-generation targeted DNA sequencing assay. Overall (OS) and progression-free survival (PFS) from re-resection were analyzed with the Kaplan-Meier method and Cox regression analyses. RESULTS: Median age at first recurrence was 57 years (range, 27-78), and median follow up from re-resection was 11 months. Salvage therapy comprised re-irradiation (n = 52, 43%), temozolomide (TMZ) (n = 39, 32%), lomustine (n = 47, 39%), and/or bevacizumab (n = 22, 18%). Median OS and PFS times were 12.1 and 4.4 months, respectively. Median tumor mutation burden (TMB) was 4 mut/Mb (range, 1-650), microsatellite instability (MSI) was 1.16% (range, 0-20), and MGMT methylation was present in 71 (59%) patients. Longer OS was found after postoperative TMZ (19.1 vs. 9.1), KPS &gt;70 (13.6 vs. 11.1), and/or re-irradiation (12.6 vs. 8.4) (p &lt; .05 for each). On multivariate analysis, TMZ (HR 0.2, 0.079-0.48), re-irradiation (HR 0.27, 0.12-0.58), and mutations in the PDGFRA (HR 0.24, 0.067-0.83) or PTEN (HR 2.3, 1.1-4.8) genes on targeted sequencing were associated with longer OS after re-resection (p &lt; .05). Multivariate predictors of re-irradiation response included MSI &gt; 1.16 (HR 0.25, 0.084-0.75), and mutations in PDGFRA (HR 0.04, 0.005-0.33), TERT (HR 0.16, 0.033-0.78), or PIK3R1 (HR 0.18, 0.041-0.8) genes. In the 46 matched primary/recurrent tumors, 40 (46%) had a longitudinal change in a mutation and 9 (24%) demonstrated hypermutation, of which 4 (57%) had simultaneous mismatch repair deficiencies. CONCLUSIONS: Our study identifies molecular factors associated with survival and response to re-irradiation in rGBM.

Abstract 6469: The association of mismatch repair gene alterations with elevated tumor mutational burden in microsatellite stable gastrointestinal cancers

Abstract Background: Benefit from single-agent immune checkpoint inhibitor has been observed in 5-10% of the patients with microsatellite stable (MSS) gastrointestinal (GI) cancers. However, a reliable predictive marker to immune checkpoint inhibitor has not been discovered in this patient population. We sought to assess the incidence of mismatch repair (MMR) gene alterations and their association with tumor mutational burden (TMB) in MSS GI cancers. Methods: This is a retrospective cohort study of patients with advanced GI cancer who had molecular profiling of the tumor using either Guardant360 blood-based or Tempus tissue next generation sequencing (NGS) platforms between 2020 and 2023. We assessed four MMR genes including MLH1, MSH2, MSH6 and PMS2 for alterations. Continuous variables were summarized as median and interquartile range (IQR) and compared using Mann-Whitney test. Categorical variables were summarized as counts and proportions and compared using Fisher’s exact test. Results: A total of 2920 patients with Guardant360 were included with a median age of 65 (IQR: 56-73) years. 870 (30%) patients had pancreas cancer; 846 (29%) patients had colorectal cancer; 688 (24%) patients had biliary tract cancers; and the rest had other GI cancers. Among patients evaluable for microsatellite instability (MSI) status, 58 patients (2%) had MSI-high GI cancers, 31 (53%) of whom had MMR gene alterations. 2445 (98%) patients had MSS GI cancers, 130 (5.3%) of whom had MMR gene alterations. Patients with MSS GI cancers bearing MMR gene alterations had a median age of 70 (IQR: 62-75) years, significantly older than those without MMR gene alterations (p&amp;lt;0.001). In addition, patients with MMR gene alterations had significantly higher median blood TMB of 11 (IQR: 7.4-16) mut/Mb compared to 7.7 (IQR: 4.8-11) mut/Mb in patients without MMR gene alterations. In MSS GI cancers, MMR gene alterations are more commonly associated with the presence of alterations in APC (p=0.03), TP53 (p=0.01), CTNNB1 (p&amp;lt;0.001) and SMAD4 (p=0.01). 1453 patients with GI cancer and Tempus tissue NGS data were included as a validation cohort. They had comparable demographics with the Guardant360 cohort. 14 (1.6%) of 896 patients with MSS GI cancers had MMR gene alterations, significantly fewer (p&amp;lt;0.001) than those found in the Guardant360 cohort. Patients with MMR gene alterations and wild type POLE had significantly higher (p=0.001) median TMB of 9.8 (IQR: 4.8-14) mut/Mb compared to 4.7 (IQR: 3.2-6.3) mut/Mb in patients without MMR gene alterations. Conclusions: MMR gene alterations can be identified by clinical NGS platforms in a small proportion of patients with MSS GI cancers. They are associated with elevated TMB, which may suggest a hypermutated profile serving as a basis for potential role of immune checkpoint inhibitor in MSS GI cancers. Citation Format: Conor D. O'Donnell, Mojun Zhu, Hao Xie. The association of mismatch repair gene alterations with elevated tumor mutational burden in microsatellite stable gastrointestinal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6469.

Abstract 2522: Predictive value of tumor mutational burden (TMB) in patients with metastatic microsatellite-stable (MSS) colorectal cancer (CRC) given first-line oxaliplatin-based chemotherapy and immune checkpoint blockade (ICB)

Abstract Purpose: Most CRC patients harbor primarily non-immunogenic MSS tumor. The randomized METIMMOX trial (NCT03388190) examined if patients with previously untreated, unresectable abdominal metastases from MSS-CRC may achieve therapeutic efficacy from short-course oxaliplatin-based chemotherapy (FLOX) and sequential ICB (nivolumab) repeatedly. Half of study patients assigned to this experimental treatment had significantly extended progression-free survival (PFS) while the other half had shortened PFS, compared to the control-group patients given standard FLOX chemotherapy with median PFS 9.3 months. Here we explored if somatic mutations (mut) unveiled by next-generation sequencing might provide insights into responsiveness to the METIMMOX regimen. Procedures: Patients had MSS-CRC with infradiaphragmatic metastases deemed unresectable and were eligible for first-line oxaliplatin-based therapy. They were randomly assigned to the control group of FLOX (oxaliplatin, 5-fluorouracil, folinic acid) Q2W or the experimental group of alternating 2 cycles each of FLOX Q2W and nivolumab Q2W, with prespecified break periods. Radiologic response assessment was done every 8 weeks with PFS as the primary endpoint. Diagnostic tumor biopsies and baseline metastasis biopsies were sequenced with the TruSight Oncology 500 assay. TMB was calculated using only coding, non-synonymous single-nucleotide variants and insertions/deletions with variant allele frequency ≥5% and sequencing depth ≥50 ×, applying the effective panel size as the megabases (Mb) denominator. Results: Sequencing data were acquired from 20 experimental-group patients with median PFS 7.9 months (minimum 2.0, maximum 41.6). Median TMB was 5.1 mut/Mb (minimum 0.8, maximum 11.8), concordant in patient-paired primary tumor and metastasis specimens. The TMB was associated with treatment outcome; the higher TMB, the better PFS with hazard ratio 0.83 (95% confidence interval (CI) 0.70-0.98; p = 0.026, Cox regression) for a PFS event with increasing TMB. TMB cut-off as low as 5.0 mut/Mb distinguished between patient groups (p = 0.007, log-rank test) with median PFS 34.9 months (95% CI 10.6-59.2; TMB&amp;gt;5, n = 10) and median PFS 4.6 months (95% CI 2.7-6.5; TMB≤5, n = 10). In the TMB&amp;gt;5 group, 8/10 were KRAS- or BRAF-mutant cases. In the TMB≤5 group, 9/10 metastasis specimens were RAS/BRAF-wildtype cases. Conclusions: TMB &amp;gt;5 mut/Mb was associated with tumor KRAS or BRAF driver mutation and remarkably long PFS in first-line treatment of patients with abdominal metastases from MSS-CRC with alternating short-course oxaliplatin-based chemotherapy and ICB. Citation Format: Anne Hansen Ree, Paula A. Bousquet, Hilde L. Nilsen, Torben Lüders, Shixiong Wang, Tina Visnovska, Diana L. Bordin, Eirik Høye, Hanne M. Hamre, Christian Kersten, Eva Hofsli, Marianne G. Guren, Halfdan Sorbye, Kjersti Flatmark, Sebastian Meltzer. Predictive value of tumor mutational burden (TMB) in patients with metastatic microsatellite-stable (MSS) colorectal cancer (CRC) given first-line oxaliplatin-based chemotherapy and immune checkpoint blockade (ICB) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2522.

Abstract 7612: Genetic predictors of anti-PD(L)-1 therapy response in hepatocellular carcinoma

Abstract Introduction: Immunotherapy targeting PD-1/PD-L1 shows promise in treating hepatocellular carcinoma (HCC), but standard predictors like PD-L1 expression are unreliable for gauging treatment response. RNA sequencing has identified a BMS 4-gene inflammatory signature that could more accurately forecast clinical outcomes. However, genomic alterations and tumor mutational burden (TMB) haven't consistently predicted anti-PD(L)-1 therapy response in HCC. Therefore, the aim of this research is to identify potential genetic alternation that could serve as predictive marker for anti-PD(L)-1 therapy responses in advanced HCC. Methods: Formalin-fixed paraffin-embedded (FFPE) tumor tissues from 38 HCC patients were analyzed using targeted next-generation sequencing with the ACTOncoTM panel before anti-PD(L)-1 therapy. This analysis identified somatic variants across 440 genes and calculated TMB. In silico tools like NetMHC and IEDB predicted neo-peptide-HLA class I binding affinity. Additionally, peripheral blood mononuclear cells provided germline data for paired TMB calculations, with tumor responses assessed by RECIST criteria. Results: Within a cohort of 167 patients with HCC undergoing ICI therapy, 35 (20.9%) responded to treatment, while 132 (79.1%) did not. Available formalin-fixed paraffin-embedded (FFPE) samples from this population included those from 14 responders and 30 non-responders. After conducting quality control measures, which assessed tumor purity, DNA quantity and integrity, as well as sequencing quality, 13 samples from responders and 25 from non-responders qualified for further analysis. Gene alteration analysis identified mutations in TP53 (47%), MUC16 (34%), CTNNB1 (32%), USH2A (16%), ARID1A (13%), NOTCH3 (13%), and ADAMTS16 (11%) of the cases. A TP53 mutation was linked to poor overall survival, whereas mutations in CTNNB1 and the RTK/RAS/RAF pathway did not correlate with clinical outcomes. The median TMB, predicted at 3.2 ± 4.3 mutations per megabase (muts/Mb), was nominally higher in patients who achieved disease control compared to non-responders (4.6 vs. 3.7 muts/Mb, p=0.53). Utilizing paired TMB analysis, those with disease control exhibited a higher TMB trend than non-responders (6.0 vs. 2.2 muts/Mb, p=0.06). Notably, the 13 cases with MUC16 mutations were associated with a significantly higher predicted TMB (10.0 vs. 3.3 muts/Mb, p=0.0015). Conclusions: This study suggests that certain genetic alterations, especially TP53 mutations, may have predictive value for the response to anti-PD(L)-1 therapy in HCC. Moreover, an elevated TMB, particularly when associated with MUC16 mutations, seems to be correlated with improved disease control. Citation Format: San-Chi Chen, Nai-Jung Chiang, MingHuang Chen, Muh-Hwa Yang. Genetic predictors of anti-PD(L)-1 therapy response in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7612.