MSI-high Status Research Articles

Expression of PD-L1 in Microsatellite Instability High Tumours: A Retrospective Study

Introduction: Microsatellite Instability (MSI) is the hallmark of Lynch syndrome/Constitutional Mismatch Repair Deficiency (CMMRD) and is also found in many sporadic cancers like colorectal cancer, endometrial, gastric, small intestine, urothelial, central nervous system and sebaceous gland neoplasms. MSI is a predictive biomarker for immunotherapy and Immunohistochemistry (IHC) antibodies against four Mismatch Repair (MMR) proteins: MutL Homolog 1 (MLH1), MutS Homolog 2 (MSH2), MutS Homolog 6 (MSH6) and Postmeiotic Segregation increased 2 (PMS2) can identify the MSI status of the tumour. In addition to MSI, immune checkpoint programmed cell death protein 1 (PD-1) expression and its ligand PD-L1 are biomarkers that can predict response to immunotherapy. Considering this increasing interest to identify deficient MMR (dMMR) status in different cancers, authors have assessed the expression of PDL1 and status of MSI in various cancer types. Aim: To evaluate the expression of PD-L1 in MSI-high status tumours. Materials and Methods: This retrospective cross-sectional study was done in the Department of Pathology, Panimalar Medical College Hospital and Research Institute for a period of six months from July 2022 to December 2022. A total of 151 cases were identified for the period of three years from January 2020 to December 2022. The slides and blocks were retrieved from the archives. Tumour sections from the paraffin embedded tissues were deparaffinised and antigen retrieval was done. IHC using four antibodies (MLH1, MH2, MSH6 and PMS2) was performed on these slides to assess the MSI status. The slides were reviewed and were further subjected to PD-L1 IHC. PD-L1 expression on tumour cells was compared with the MSI status of different cancer types. The p-value was calculated using t-test and p<0.5 was considered statistically significant. Statistical analysis was done using International Business Machines (IBM) Statistical Package for the Social Sciences (SPSS) software version 21.0. Results: A total of 151 cases were included in the present study. A positive nuclear stain for the four MMR proteins denote expression of wild type MMR proteins, hence MSI low status. A loss of nuclear expression denotes mutation of MMR proteins and hence MSI high (MSI-H) status. The MSI was high in nine out of 48 cases (18.75%) of colon cancer, three out of 15 cases (20%) of endometrial cancers, three out of 20 cases (15%) of gastric cancers. Rest were one out of sixteen cases of ovarian cancer, one out of two malignant melanoma and one out of three glioblastoma. Out of these, PD-L1 was positive in seven of the 18 MSI-H cases (38.88% of MSI-H cases). The MSI was low/ stable in the remaining 133 cases. The p-value of significance was 0.03 (statistically significant). Conclusion: This study shows a significant association of MSI-H with PD-L1 expression in tumours. Further large scale studies can help in assessing the role of PD-L1 as an effective therapeutic biomarker in MSI-high status patients who can benefit from targeted therapy

Molecular Characteristics of Early-Onset Colorectal Cancer According to Detailed Anatomical Locations: Comparison With Later-Onset Cases.

Early-onset colorectal cancer diagnosed before the age of 50 years has been increasing. Likely reflecting the pathogenic role of the intestinal microbiome, which gradually changes across the entire colorectal length, the prevalence of certain tumor molecular characteristics gradually changes along colorectal subsites. Understanding how colorectal tumor molecular features differ by age and tumor location is important in personalized patient management. Using 14,004 cases with colorectal cancer including 3,089 early-onset cases, we examined microsatellite instability (MSI), CpG island methylator phenotype (CIMP), and KRAS and BRAF mutations in carcinomas of the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum and compared early-onset cases with later-onset cases. The proportions of MSI-high, CIMP-high, and BRAF -mutated early-onset tumors were lowest in the rectum (8.8%, 3.4%, and 3.5%, respectively) and highest in the ascending colon (46% MSI-high; 15% CIMP-high) or transverse colon (8.6% BRAF -mutated) (all Ptrend <0.001 across the rectum to ascending colon). Compared with later-onset tumors, early-onset tumors showed a higher prevalence of MSI-high status and a lower prevalence of CIMP-high status and BRAF mutations in most subsites. KRAS mutation prevalence was higher in the cecum compared with that in the other subsites in both early-onset and later-onset tumors ( P < 0.001). Notably, later-onset MSI-high tumors showed a continuous decrease in KRAS mutation prevalence from the rectum (36%) to ascending colon (9%; Ptrend <0.001), followed by an increase in the cecum (14%), while early-onset MSI-high cancers showed no such trend. Our findings support biogeographical and pathogenic heterogeneity of colorectal carcinomas in different colorectal subsites and age groups.

Distinct clinical pattern of colorectal cancer patients with POLE mutations: A retrospective study on real-world data.

Objective: Studies have demonstrated an association between somatic POLE exonuclease domain mutations (EDMs) and the prognosis of colorectal cancer (CRC). However, the prognostic value of POLE non-EDMs remains unclear. This retrospective study aimed to explore the possible relationships between POLE mutation subtypes and CRC prognosis. Methods: The 272 CRC patients from the First Affiliated Hospital of Zhengzhou University (ZZ cohort) and 499 CRC patients from The Cancer Genome Atlas database (TCGA cohort) were retrospectively collected. The cases were divided into subgroups based on POLE mutation sites and microsatellite instability (MSI) status. The continuous variables were compared among three subgroups with Kruskal-Wallis tests. Pairwise comparisons between three groups were performed by Bonferroni correction method, and adjusted p < 0.05 was considered statistically significant. The categorical variables were compared with Chi-square test and Fisher's exact test. The Kaplan-Meier curves and Cox regression models were conducted to evaluate prognostic values of POLE mutations. Results: In the ZZ cohort, POLE EDMs (2.6%) were significantly associated with younger age (p = 0.018) and localized in the left colon (p = 0.001). POLE non-EDMs were significantly associated with MSI-high status (p < 0.001) and localization in the right colon (p = 0.001). In the TCGA cohort, the tumor mutation burden (TMB) of both POLE EDM tumors (p < 0.001) and POLE non-EDM tumors (p < 0.001) was significantly higher than that of POLE wild-type (WT) tumors. A similar trend was observed in the ZZ cohort, although there were no significant differences. In the ZZ cohort, the POLE EDM group had higher progression-free survival (PFS) (p = 0.002) and overall survival (OS) (p = 0.042) than the POLE non-EDM group and POLE WT group. We also report one CRC patient harboring a germline POLE mutation who received camrelizumab and exhibited long-term stable disease. Conclusion: Both POLE-EDMs and POLE non-EDMs were associated with significantly increased TMB in CRC and may be biomarkers for CRC treatment and prognosis. Current evidence does not support an effect of POLE non-EDMs on PFS and OS. A significant association between POLE EDMs and improved PFS and OS may exist, but future studies with larger sample sizes are needed. Entire coding region of the POLE gene should be screened.

SWI/SNF complex gene variations are associated with a higher tumor mutational burden and a better response to immune checkpoint inhibitor treatment: a pan-cancer analysis of next-generation sequencing data corresponding to 4591 cases

BackgroundGenes related to the SWItch/sucrose nonfermentable (SWI/SNF) chromatin remodeling complex are frequently mutated across cancers. SWI/SNF-mutant tumors are vulnerable to synthetic lethal inhibitors. However, the landscape of SWI/SNF mutations and their associations with tumor mutational burden (TMB), microsatellite instability (MSI) status, and response to immune checkpoint inhibitors (ICIs) have not been elucidated in large real-world Chinese patient cohorts.MethodsThe mutational rates and variation types of six SWI/SNF complex genes (ARID1A, ARID1B, ARID2, SMARCA4, SMARCB1, and PBRM1) were analyzed retrospectively by integrating next-generation sequencing data of 4591 cases covering 18 cancer types. Thereafter, characteristics of SWI/SNF mutations were depicted and the TMB and MSI status and therapeutic effects of ICIs in the SWI/SNF-mutant and SWI/SNF-non-mutant groups were compared.ResultsSWI/SNF mutations were observed in 21.8% of tumors. Endometrial (54.1%), gallbladder and biliary tract (43.4%), and gastric (33.9%) cancers exhibited remarkably higher SWI/SNF mutational rates than other malignancies. Further, ARID1A was the most frequently mutated SWI/SNF gene, and ARID1A D1850fs was identified as relatively crucial. The TMB value, TMB-high (TMB-H), and MSI-high (MSI-H) proportions corresponding to SWI/SNF-mutant cancers were significantly higher than those corresponding to SWI/SNF-non-mutant cancers (25.8 vs. 5.6 mutations/Mb, 44.3% vs. 10.3%, and 16.0% vs. 0.9%, respectively; all p < 0.0001). Furthermore, these indices were even higher for tumors with co-mutations of SWI/SNF genes and MLL2/3. Regarding immunotherapeutic effects, patients with SWI/SNF variations showed significantly longer progression-free survival (PFS) rates than their SWI/SNF-non-mutant counterparts (hazard ratio [HR], 0.56 [95% confidence interval {CI} 0.44–0.72]; p < 0.0001), and PBRM1 mutations were associated with relatively better ICI treatment outcomes than the other SWI/SNF gene mutations (HR, 0.21 [95% CI 0.12–0.37]; p = 0.0007). Additionally, patients in the SWI/SNF-mutant + TMB-H (HR, 0.48 [95% CI 0.37–0.54]; p < 0.0001) cohorts had longer PFS rates than those in the SWI/SNF-non-mutant + TMB-low cohort.ConclusionsSWI/SNF complex genes are frequently mutated and are closely associated with TMB-H status, MSI-H status, and superior ICI treatment response in several cancers, such as colorectal cancer, gastric cancer, and non-small cell lung cancer. These findings emphasize the necessity and importance of molecular-level detection and interpretation of SWI/SNF complex mutations.

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

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

19P Deciphering the role of precision oncology in the treatment of biliary tract cancer in daily routine practice: Retrospective analysis from the cancer center Upper Austria

BackgroundThe routine therapeutic landscape of metastatic CCC is still largely based on cytotoxic chemotherapy. This standard gets increasingly challenged with the advent of next generation sequencing (NGS) in routine practice and evolving trials of targeted therapies in CCC. However the value of comprehensive genetic profiling of CCC in actual routine clinical practice remains poorly characterized.MethodsWe performed a retrospective study at the clinical cancer center of Upper Austria (Tumorzentrum Oberösterreich) in 2018-2021. Tumor samples from 56 patients with advanced CCC underwent comprehensive genetic profiling. TruSight Tumor 170 Assay (Illumina), Archer FusionPlex Panel (ArcherDX), Oncomine Focus Assay (Thermo Fisher Scientific) were used for NGS analysis. Furthermore MSI status was determined by custom made Multiplex PCR-Based Methods. Immunhistochemistry (IHC) collected data on Her2neu and PDL-1expression.ResultsA potentially actionable pathogenic variant was identified in 32 patients (57%). Pathogenic variants were ranked according ESMO Scale for Clinical Actionability of molecular Targets (ESCAT). In 15 patients with ESCAT I-III criteria a molecular informed therapy was established targeting 8 FGFR alterations, 2 MSI high status, 1 Pi3kinase mutation, 2 BRCA1/2 mutations, 2 BRAF V600Emutations. In 13 of the 15 treated patients we could observe a favorable PFS2 (targeted therapy)/PFS1 (previous standard therapy) ratio >1,3, suggesting clinical benefit. Overall survival in patients receiving molecular matched therapy showed a positive trend compared to patients remaining on standard treatment protocol.ConclusionsWe could show that comprehensive molecular characterization of advanced CCC during routine clinical care leads to favorable PFS2/PFS1 ratios and probable positive overall survival. This underscores the recent ESMO recommendations for NGS reflex testing in advanced CCC.Legal entity responsible for the studyThe authors.FundingHas not received any funding.DisclosureAll authors have declared no conflicts of interest. BackgroundThe routine therapeutic landscape of metastatic CCC is still largely based on cytotoxic chemotherapy. This standard gets increasingly challenged with the advent of next generation sequencing (NGS) in routine practice and evolving trials of targeted therapies in CCC. However the value of comprehensive genetic profiling of CCC in actual routine clinical practice remains poorly characterized. The routine therapeutic landscape of metastatic CCC is still largely based on cytotoxic chemotherapy. This standard gets increasingly challenged with the advent of next generation sequencing (NGS) in routine practice and evolving trials of targeted therapies in CCC. However the value of comprehensive genetic profiling of CCC in actual routine clinical practice remains poorly characterized. MethodsWe performed a retrospective study at the clinical cancer center of Upper Austria (Tumorzentrum Oberösterreich) in 2018-2021. Tumor samples from 56 patients with advanced CCC underwent comprehensive genetic profiling. TruSight Tumor 170 Assay (Illumina), Archer FusionPlex Panel (ArcherDX), Oncomine Focus Assay (Thermo Fisher Scientific) were used for NGS analysis. Furthermore MSI status was determined by custom made Multiplex PCR-Based Methods. Immunhistochemistry (IHC) collected data on Her2neu and PDL-1expression. We performed a retrospective study at the clinical cancer center of Upper Austria (Tumorzentrum Oberösterreich) in 2018-2021. Tumor samples from 56 patients with advanced CCC underwent comprehensive genetic profiling. TruSight Tumor 170 Assay (Illumina), Archer FusionPlex Panel (ArcherDX), Oncomine Focus Assay (Thermo Fisher Scientific) were used for NGS analysis. Furthermore MSI status was determined by custom made Multiplex PCR-Based Methods. Immunhistochemistry (IHC) collected data on Her2neu and PDL-1expression. ResultsA potentially actionable pathogenic variant was identified in 32 patients (57%). Pathogenic variants were ranked according ESMO Scale for Clinical Actionability of molecular Targets (ESCAT). In 15 patients with ESCAT I-III criteria a molecular informed therapy was established targeting 8 FGFR alterations, 2 MSI high status, 1 Pi3kinase mutation, 2 BRCA1/2 mutations, 2 BRAF V600Emutations. In 13 of the 15 treated patients we could observe a favorable PFS2 (targeted therapy)/PFS1 (previous standard therapy) ratio >1,3, suggesting clinical benefit. Overall survival in patients receiving molecular matched therapy showed a positive trend compared to patients remaining on standard treatment protocol. A potentially actionable pathogenic variant was identified in 32 patients (57%). Pathogenic variants were ranked according ESMO Scale for Clinical Actionability of molecular Targets (ESCAT). In 15 patients with ESCAT I-III criteria a molecular informed therapy was established targeting 8 FGFR alterations, 2 MSI high status, 1 Pi3kinase mutation, 2 BRCA1/2 mutations, 2 BRAF V600Emutations. In 13 of the 15 treated patients we could observe a favorable PFS2 (targeted therapy)/PFS1 (previous standard therapy) ratio >1,3, suggesting clinical benefit. Overall survival in patients receiving molecular matched therapy showed a positive trend compared to patients remaining on standard treatment protocol. ConclusionsWe could show that comprehensive molecular characterization of advanced CCC during routine clinical care leads to favorable PFS2/PFS1 ratios and probable positive overall survival. This underscores the recent ESMO recommendations for NGS reflex testing in advanced CCC. We could show that comprehensive molecular characterization of advanced CCC during routine clinical care leads to favorable PFS2/PFS1 ratios and probable positive overall survival. This underscores the recent ESMO recommendations for NGS reflex testing in advanced CCC.

Surgical Resection for Local and Lateral Lymph Node Recurrence of MSI-high Cecal Cancer with the BRAF V600E Mutation.

An 84-year-old female underwent open right hemicolectomy with D3 lymph node dissection for cecal cancer, pathologically identified as pT4aN2M0 Stage IIIc and BRAF mutation-positive. Due to early recurrence of abdominal wall and right lateral lymph nodes, the patient was treated with FOLFOXIRI+Bevacizumab. Imaging after 5 courses of chemotherapy found tumor shrinkage and no new metastases. The patient did not tolerate chemotherapy well, and tumor resection was performed. Microsatellite instability (MSI) testing using multiplex polymerase chain reaction (PCR) fragment analysis revealed MSI-high status. The patient is currently recurrence-free without chemotherapy at 1 year postoperatively. BRAF-mutated colorectal cancer has a poor prognosis, and may require resection of the metastatic or recurrent tumor after comprehensive evaluation.

Abstract 1263: Comprehensive genomic profiling to identify biomarkers predictive of response to immunotherapy

Abstract Background: Immune-oncology (I-O) drugs show promise across multiple tumor types, and several biomarkers (BM) predict responsiveness to I-O therapy. In this descriptive study of clinical lab experience (2018-2021), we investigated the prevalence of genomic BMs associated with sensitivity and resistance to I-O drugs across solid tumors. Methods: The GEM ExTra® assay was used to exome-sequence 2,359 paired samples at 180X and 400X coverage for germline and tumor DNA respectively. Reportable alterations were single base substitutions, indels, copy number alterations, fusions, alternate transcripts, as well as tumor mutational burden (TMB) and microsatellite instability (MSI) status. For I-O sensitive BMs we recorded MSI-High status, TMB-High (&amp;gt; 10 mut/Mb) status, and mutations in POLE/POLD1, MLH1, MSH2/3/6, PMS1/2, PD-L1/-L2, CTLA4, CD28, ARID2, and PBRM1. For I-O resistance BMs, IDO1 amplification and mutations in B2M, JAK1/2, IDO1, KRAS and STK11 were tallied. Results: I-O sensitive BMs varied from 0% to 58% (results in Table 1 for selected tumor types). Overall, TMB-High was in 6% of samples and MSI-High in 3%; all MSI-High were also TMB-High. In the 46% of renal cell carcinoma samples with I-O-sensitive BMs, PBRM1 mutation was common (94%). In 3 TMB-High endometrial samples, POLE/POLD1 was mutated, indicative of an ultra-mutated phenotype. Of note, 35% of colorectal cancer and 8% of melanoma samples with I-O sensitive mutations also had loss-of-function mutations in JAK1/2 and B2M, suggestive of I-O resistance. In non-small cell lung cancer, co-mutation of STK11 and KRAS, suggesting inferior response to I-O therapy, was present in 4% of samples with I-O BMs. IDO1 amplification was present in less than 1% of entire cohort. Conclusions: Our study found I-O sensitive BMs in common and in rare aggressive cancers. The GEM ExTra assay can stratify cancer patients for likely responsiveness to immunotherapy. Table 1. Immune-oncology sensitive biomarkers observed across select tumors Solid tumor type % of samples with signature All (n = 2,360) 13% Melanoma (n = 50) 54% Other skin cancers (n = 13) 62% Renal cell carcinoma (n = 200) 46% Urothelial (n = 86) 22% Endometrial (n = 88) 20% Gastro-intestinal (n = 360) 12% Sarcoma (n = 90) 11% Prostate (n = 151) 6% Lung (n = 100) 4% Breast (n = 297) 2% Central nervous system (n = 60) 0% Citation Format: Pawan Noel, David W. Hall, Sameer S. Udhane, Min Wang, Fadel S. Alyaqoub, Szabolcs Szelinger, Audrey A. Ozols, Janine R. LoBello, Frederick L. Baehner, Gargi D. Basu. Comprehensive genomic profiling to identify biomarkers predictive of response to immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1263.

Evaluation of circulating tumor cells in stage III colorectal cancer patients under three or six months of adjuvant therapy.

e15601 Background: The duration of adjuvant oxaliplatin-combination treatment in stage III colorectal cancer (CRC) patients is still debatable. Circulating Tumor Cells (CTCs) have been proposed as a potential markers for detection of micrometastatic disease. The aim was to compare the elimination rate of CTCs in patients treated with three- and six-months treatment with FOLFOX or CAPOX, in stage III CRC patients. Methods: Peripheral blood samples were collected from 132 patients at baseline, after three (for all patients) and after six months (for those under six months treatment). Surgical specimens were collected from all patients for the evaluation of their genetic profiling using Sanger sequencing (Ras/Raf) and fragment analysis (microsatellite instability status). The detection and number of circulating tumor cells (CTCs) were evaluated using double immunofluorescence and a real time-polymerase chain reaction assay, at all three time points. Results: Median age of the patients was 62 years, 59.8% were males, 92.7% had a colon/sigmoid tumor location, 24.4% had tumor on the right colon and 99.2% had a good performance status (PS). Of all patients, 44.3% and 55.7% were treated with FOLFOX and CAPOX, respectively; patients received treatment for three and six months, were equally distributed. KRAS, NRAS and BRAFmutations were detected in 41.5%, 2.1% and 12.8%, respectively; whereas MSI-High status was detected in 9.8% of the patients. CTCs were detected in 43.2%, 42.4% and 54.2% of the patients, at baseline, after three and six months of treatment, respectively. Both positivity rate ( p&lt; 0.001) and absolute number of CTCs ( p= 0.022) were decreased between baseline and three months of treatment. Moreover, a significant increase was observed both on the positivity rate ( p= 0.053) and absolute number of CTCs ( p&lt; 0.001) between three and six months of treatment. Following Cox regression analysis, BRAF status and the detection of CTCs are significantly correlated with decreased time to progression. Conclusions: To conclude, the current study indicates that 3 months of adjuvant treatment is at least as efficacious as 6 months in eliminating CTCs. However, the increase of both the rate and number of positive CTCs after three months of treatment might highlight the emergence of resistant cancer cell clones.

Association of RB1 mutational status with overall genomic landscape in neuroendocrine prostate cancer (NEPC).

5063 Background: NEPC is a high-grade aggressive form of prostate cancer. We queried whether RB1 mutation status would impact the genomic features of NEPC in RB1 mutated vs non-mutated cases. Methods: From a series of 13,496 cases of clinically advanced PC, we identified 415 cases (3.1%) with a diagnosis of small cell PC or NEPC as determined by the submitting physician. They were sequenced using a hybrid capture-based FDA-approved clinical genomic profiling (CGP) assay to detect all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on 0.8 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 95 loci. PD-L1 expression was determined by IHC (Dako 22C3) with low tumor cell positive staining 1-49% and high staining ≥50% expression. Results: 253 (61%) of NEPC feature GA in RB1 (RB1 mut+). This contrasts with a 5.8% frequency of RB1 GA in the non-NEPC (P &lt;.0001). The RB1 mut+ NEPC featured a slightly greater number of pathogenic GA/tumor than the RB1 mut- NEPC (5.1 vs 4.2). Age and TMPRSS2-ERG fusion frequency were similar between the groups. RB1 Mut- NEPC was associated with significantly higher amplifications (amp) and total GA in AR compared to RB1 mut+ NEPC. RB1 mut+ NEPC featured significantly greater frequency of PTEN GA. GA frequencies in targetable kinases and DNA repair GA including BRCA1/2 and ATM linked to PARP inhibitor (PARPi) response were similar in both groups. For potential immune-oncology (IO) biomarkers, RB1 Mut+ NEPC featured significantly greater frequency of positive PD-L1 expression and lower frequencies of MDM2 and CDK12 GA. CD274 ( PD-L1) amplification, MSI-high status and cases with TMB ≥10 mut/Mb were uncommon in both groups. gLOH was higher in RB1 mut+ than RB1 mut- (P =.005). There were more cases of non-European ancestry in the RB1 mut- group. APC I1307K mut were found in 3/162 (1.9%) RB1 mut- NEPC only. Conclusions: In NEPC, the presence of RB1 mutation is associated with various GA that may have clinical relevance. Further study of RB1 status as a guide in trial designs on therapy selection for men with NEPC appears warranted. [Table: see text]

Concordance Study of a 520-Gene Next-Generation Sequencing-Based Genomic Profiling Assay of Tissue and Plasma Samples.

Next-generation sequencing (NGS) enables simultaneous detection of actionable somatic variants and estimation of genomic signatures such as tumor mutational burden (TMB) or microsatellite instability (MSI) status, which empowers therapeutic decisions in clinical oncology. Our retrospective study investigated the clinical performance of somatic variant detection in paired tissue and blood samples using a large targeted gene panel, the OncoScreen Plus, which interrogates 520 cancer-related genes. We analyzed sequencing data derived from paired tissue and blood samples of 3005 patients spanning 20 solid tumor types, including lung (n = 1971), gastrointestinal (n = 625), breast (n = 120) and gynecological (n = 110), genitourinary (n = 38), and other cancers (n = 141). Across tumor types, the OncoScreen Plus panel achieved a high tissue detection rate, with an average of 97.9%. The average plasma detection rate was 72.2%, with an average tissue concordance rate of 36.6%. Considering all variant types, the plasma assay yielded an average sensitivity/true positive rate of 45.7%, with a positive predictive value of 64.7% relative to tissue assay. Pearson correlation analysis revealed a strong correlation in TMB estimated from blood and tissue samples (correlation coefficient 0.845, R2 = 0.756). MSI-high status was identified in five tumor types, including endometrial cancer (28.6%), colorectal cancer (2.5%), ovarian cancer (2.0%), gastric cancer (1.5%), and lung adenocarcinoma (0.2%). Paired tumor and blood samples from a large cohort of patients spanning 20 tumor types demonstrated that the OncoScreen Plus is a reliable pan-cancer panel for the accurate detection of somatic variants and genomic signatures that could guide individualized treatment strategies to improve the care of patients with advanced cancer.

Genomic classification of clinically advanced major genito-urinary cancers (GUca) based on methylthioadenosine phosphorylase (MTAP) genomic loss.

164 Background: Novel treatments for clinically advanced GUca including castrate resistant prostate ca (PC), bladder urothelial ca (BUC) and clear cell renal ca (ccRCC) are widely needed. Recently, the targeting of cancer cells with arginine accumulation caused by MTAP loss has emerged as a new synthetic lethality-based anti-cancer program. Methods: 8,436 mCRPC, 2,683 BUC and 841 ccRCC underwent hybrid-capture based comprehensive genomic profiling (CGP) to evaluate all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on up to 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on up to 114 loci. PD-L1 tumor cell expression was determined by IHC (Dako 22C3). Results: 1.3% of PC, 24.2% of BUC and 5.5% of ccRCC featured MTAP loss. There were no significant age or gender differences associated with MTAP loss. CDKN2A/B loss ranged from 94% in ccRCC to &gt; 99% in PC and BUC. The GA/tumor frequencies were similar when CDKN2A/B GA are excluded. In PC, GA in TP53, PTEN and BRCA1 were more frequent, while GA in AR, CDK12, RB1 and BRCA2 were less frequent in cases with MTAP loss. In BUC, GA in TSC1 and FGFR3 were more frequent and GA in RB1and TP53 were less frequent in cases with MTAP loss. In ccRCC, GA in NF2 were more frequent in cases with MTAP loss, while GA in VHL and PBRM1 were less frequent in cases with MTAP loss. “Targetable” kinase GA were rare in all groups, except for FGFR3 GA in MTAP loss BUC. Immunotherapy (IO) putative biomarkers varied among tumors, with MSI-high status less frequent and TMB ≥ 10 mut/Mb more frequent in BUC MTAP-intact than BUC with MTAP loss. PD-L1 expression was similar except for high PD-L1 expression more frequent in MTAP-intact BUC. Conclusions: When compared with PC and ccRCC, the clinical development of novel drugs, such as PRMT5 and MTA2 inhibitors in GUca will likely be focused on BUC given the 24% frequency of MTAP loss in that tumor type. CGP of PC, BUC and ccRCC reveal significant differences in GA in MTAP-intact and tumors with MTAP loss, which may impact future combinatorial clinical trial designs.[Table: see text]

Association of RB1 mutational status with overall genomic landscape in neuroendocrine prostate cancer (NEPC).

156 Background: NEPC is a high-grade aggressive form of prostate cancer. We queried whether RB1 mutation status would impact the genomic features of NEPC. We hypothesized that there would be differences in GA frequencies in RB1 mutated vs non mutated cases. Methods: From a series of 13,496 cases of clinically advanced PC, 415 (3.1%) histologically defined NEPC were sequenced using a hybrid capture-based FDA-approved clinical genomic profiling (CGP) assay to detect all classes of genomic alterations (GA). Tumor mutational burden (TMB) was determined on 0.8 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 95 loci. PD-L1 expression was determined by IHC (Dako 22C3) with low tumor cell positive staining 1-49% and high staining ≥50% expression. Results: 253 (61%) of NEPC feature GA in RB1 (RB1 mut+). This contrasts with a 5.8% frequency of RB1 GA in the non-NEPC (P &lt;.0001). The RB1 mut+ NEPC featured a slightly greater number of driver GA/tumor than the RB1 mut- NEPC (5.1 vs 4.2). Age and TMPRSS2-ERG fusion frequency were similar between the groups. RB1 Mut- NEPC was associated with significantly higher amplifications (amp) and total GA in AR compared to RB1 mut+ NEPC. RB1 mut+ NEPC featured significantly greater frequency of PTEN GA. GA frequencies in targetable kinases and DNA repair GA including BRCA1/2 and ATM linked to PARP inhibitor (PARPi) response were similar in both groups. For potential immune-oncology (IO) biomarkers, RB1 Mut+ NEPC featured significantly greater frequency of low positive PD-L1 expression and lower frequencies of MDM2 and CDK12 GA. CD274 ( PD-L1) amplification, MSI-high status and cases with TMB ≥10 mut/Mb were very uncommon in both groups. Conclusions: In NEPC, the presence of RB1 mutation is associated with various GA that may have clinical relevance. Limitations include possible selection and confounding biases, and lack of clinical annotation. Further study of RB1 status as a guide of trial designs on therapy selection for men with NEPC is warranted.[Table: see text]

Abstract P3-08-04: The genomic and transcriptomic landscape of PIK3R1 mutated breast cancers

Abstract Background: Human breast cancers may harbor pathogenic somatic alterations in PIK3R1, which encodes the regulatory subunit—p85a—of the PI3K signaling complex. Prior studies developed an isogenic cellular system lacking p85a and investigated therapeutic approaches for breast cancers that lack functional p85a. For instance, somatic loss of PIK3R1 may sensitize breast cancer cells to MEK inhibition; work in patient-derived xenograft models confirmed this observation. Here, we wanted to investigate the significance of PIK3R1 mutations (PIK3R1MUT) in human breast cancer by using real-world data to characterize the genomic landscape of breast cancer patients with PIK3R1MUT. Additionally, our methodology allows us to assess the effect of PIK3R1MUT on corresponding mRNA expression-levels, tumor mutational burden (TMB), and microsatellite instability (MSI) to better understand the molecular-level effects of this important gene. Methods: We used the Tempus LENS platform to retrospectively analyze next-generation sequencing (NGS) data from 3400 HER2-negative (HER2-) advanced or metastatic breast cancer patients with confirmed hormone receptor status (HR+/-). Our cohort consisted of molecularly profiled, deidentified breast cancer cases using the Tempus xT solid tumor assay (DNA-seq of 595-648 genes at 500x coverage, and full transcriptome RNA-seq). This assay assesses mutations in both germline and somatic tissue, and characterizes nucleotide variants, insertions/deletions, and copy number variations. Results: The prevalence of PIK3R1MUT in HER2- breast cancer was 2.3% (77/3400). PIK3R1MUT occurred more frequently than expected in HR- breast cancer relative to the proportion we observed for wild-type PIK3R1 (Chi-squared test, p&amp;lt;0.001). In the HR+ subtype, high TMB (defined as 10 mutations/MB) occurred more frequently in PIK3R1MUT tumors than in samples with wild-type PIK3R1 (PIK3R1WT) status (Fisher’s exact test, p=0.039). Further, MSI-high status was absent in PIK3R1MUT tumors but was observed in PIK3R1WT samples. We assessed co-mutational patterns and found that pathogenic or likely pathogenic mutations in PTEN, TP53. and NF1 were more frequent in PIK3R1MUT samples, whereas mutations in PIK3CA were more frequent in the PIK3R1WT cohort (Table 1). At the transcriptional-level, PIK3R1 expression was similar in HR+ samples regardless of PIK3R1 mutational status but PIK3R1 transcript expression was significantly higher among PIK3R1MUT samples (Wilcoxon rank-sum test, p&amp;lt;0.001). Conclusions: Our study used real-world evidence to build on previous pre-clinical studies, and illustrates the importance of PIK3R1MUT in breast cancer. We found that certain mutations associated with poor outcomes and endocrine therapy resistance (e.g., PTEN, and NF1) were more frequent in PIK3R1MUT tumor samples. Interestingly, we did not find evidence that PIK3R1MUT results in decreased PIK3R1 mRNA expression but instead observed that in the HR- subtype PIK3R1MUT gene expression was significantly higher. Overall, this study shows that PIK3R1 may be an important therapeutic target in breast cancer. Table 1.- Co-mutations and PIK3R1 transcript abundance in PIK3R1MUT vs PIK3R1WT samples.Correlation of Gene Co-mutations with PIK3R1MUTGenesPIK3R1MUT (n=77)n (%)PIK3R1WT (n=3323)n (%)p-valuePositively correlatedPTEN21 (27%)176 (5.3%)&amp;lt;0.001NF113 (17%)134 (4.0%)&amp;lt;0.001TP5344 (57%)1289 (39)0.001Negatively CorrelatedPIK3CA9 (12%)861 (26%)0.005PIK3R1 gene expressionSub-typeNormalized expressionNormalized expressionp-valueHR+3.34 (n=30)3.28 (n=1720)0.2HR-3.45 (n=33)3.23 (n=678)&amp;lt;0.001 Citation Format: Melody Cobleigh, Emmanuel Okeke, Brett Mahon, Elizabeth Mauer, Alex Barrett, Abde Abukhdeir. The genomic and transcriptomic landscape of PIK3R1 mutated breast cancers [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-08-04.

Abstract P086: Identification of pharmacodynamic and sensitivity biomarkers for TACH101, a pan-inhibitor of KDM4 histone lysine demethylase

Abstract Background: TACH101 is a novel, selective and potent inhibitor of KDM4 in development for advanced cancers. KDM4 plays a key role in epigenetic regulation by removing methyl marks on histone H3K9 and H3K36. Overexpression of KDM4 leads to dysregulation of transcription, cell cycle, and DNA replication/repair processes and has been associated with many cancer types. Methods: Candidate pharmacodynamic (PD) and sensitivity biomarkers for TACH101 were evaluated in vitro and in vivo using cancer cell lines, mouse xenograft models, gene microarrays, ChIP-seq, and ChIP-qPCR. Results: Evaluation of differential gene expression from tumor tissue identified several candidates as potential PD markers for TACH101 activity. In particular, direct binding of KDM4 to Protein Phosphatase 1 Regulatory subunit 10 (PPP1R10 or PNUTS) was confirmed by ChIP-seq in cell lines from esophageal (KYSE-150), breast (MDA-MB-231) and lymphoma (OCI-Ly19) cancers. TACH101 treatment caused 86% repression of PNUTS mRNA, as well as a 51% increase in H3K9me3, a mark of repressed transcription. A 78% decrease in H3K36me3 at the PNUTS gene was also observed. PNUTS as a target of KDM4 was validated via ChIP-qPCR in xenograft tumors of KYSE-150, OCI-Ly19 and SU-60 (colorectal). In vivo, maximum inhibition of PNUTS was reached at 8 hours post TACH101 administration, when TACH101 concentration was 100-200 nM in tumors. In addition, extensive bioinformatics analysis using &amp;gt;300 cancer cell lines showed that cell lines with MSI-high (MSI-H) status tended to be more sensitive to TACH101 in vitro. This association was found with other markers of MSI-H status such as MMR gene mutations, MLH1 methylation status, and overall mutation frequency. To further test this association, TACH101 was evaluated in a panel of patient-derived xenograft (PDX) and organoid models. The results showed a strong correlation of TACH101 sensitivity with MSI-H status (IC50 ranges 1-150 nM). Conclusions: Candidate PD biomarkers of TACH101 activity for clinical evaluation have been identified and further studies are ongoing to explore current and additional markers. In addition, MSI-H status was associated with increased sensitivity to TACH101, which may be useful for enriching for select patient populations in clinical studies. Citation Format: Frank Perabo, Sanghee Yoo, Chandtip Chandhasin, Joselyn Del Rosario, Young K. Chen, Ellen Filvaroff, Jeffrey A. Stafford, Stephen Quake, Michael F. Clarke. Identification of pharmacodynamic and sensitivity biomarkers for TACH101, a pan-inhibitor of KDM4 histone lysine demethylase [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P086.

Radiogenomic and Deep Learning Network Approaches to Predict KRAS Mutation and Microsatellite Instability Status From Radiotherapy Plan

<h3>Purpose/Objective(s)</h3> We aimed to investigate the role of radiogenomic and deep learning approaches in predicting the KRAS mutation and microsatellite instability (MSI) status of a tumor using the radiotherapy planning computed tomography (CT) images of 110 patients who received neoadjuvant concurrent chemoradiation for locally advanced rectal cancer. <h3>Materials/Methods</h3> After surgical resection, 30 (27.3%) tumors were found to have KRAS mutation and 2 (1.8%) had MSI-high status. We adopted both the radiogenomic and deep learning approaches to predict KRAS mutation and MSI. A total of 378 texture features were extracted from the boost clinical target volume (CTV) in the radiotherapy planning CT images. The least absolute shrinkage and selection operator method was performed to select the features associated with KRAS and MSI status. Tuning parameter (λ) was determined by 10-fold cross validation. The radiogenomic score was calculated by combining the coefficients of the selected features. Meanwhile, we developed a deep learning network based on the three-dimensional input of the CTV. Performance of models was internally validated. <h3>Results</h3> The predictive ability of the radiogenomic score model revealed AUCs of 0.73 for KRAS mutation and 0.99 for MSI status, whereas that for the deep learning model demonstrated worse performance, with AUCs of 0.63 for KRAS and 0.58 for MSI. <h3>Conclusion</h3> Compared with the deep learning network model, the radiogenomic score model was a more feasible approach to predict KRAS and MSI status. These results should be externally validated on a larger dataset

TremelImumab and Durvalumab Combination for the Non-OperatIve Management (NOM) of Microsatellite InstabiliTY (MSI)-High Resectable Gastric or Gastroesophageal Junction Cancer: The Multicentre, Single-Arm, Multi-Cohort, Phase II INFINITY Study.

Simple SummaryThe status of microsatellite instability (MSI-H) in gastric or gastroesophageal junction cancer (GC/GEJC) patients eligible for radical surgery proved to be prognostic for an improved survival outcome and predictive for poor/no benefit from the combination of adjuvant/peri-operative chemotherapy. MSI-H tumors display a high sensitivity to immunotherapy and exploratory studies showed that a pre-operative treatment with immune-checkpoint inhibitors may achieve elevated rates of pathological complete responses. The ongoing proof-of-concept INFINITY study is aimed at investigating the role of the combo-immunotherapy durvalumab plus tremelimumab as a neoadjuvant or potentially definitive treatment (avoiding surgery in case of complete clinical response) for MSI-H resectable GC/GEJC patients.In resectable gastric or gastroesophageal junction cancer (GC/GEJC), the powerful positive prognostic effect and the potential predictive value for a lack of benefit from the combination of adjuvant/peri-operative chemotherapy for the MSI-high status was demonstrated. Given the high sensitivity of MSI-high tumors for immunotherapy, exploratory trials showed that combination immunotherapy induces a high rate of complete pathological response (pCR), potentially achieving cancer cure without surgery. INFINITY is an ongoing phase II, multicentre, single-arm, multi-cohort trial investigating the activity and safety of tremelimumab and durvalumab as neoadjuvant (Cohort 1) or potentially definitive (Cohort 2) treatment for MSI-high/dMMR/EBV-negative, resectable GC/GEJC. About 310 patients will be pre-screened, to enroll a total of 31 patients, 18 and 13 in Cohort 1 and 2, at 25 Italian Centres. The primary endpoint of Cohort 1 is rate of pCR (ypT0N0) and negative ctDNA after neoadjuvant immunotherapy, of Cohort 2 is 2-year complete response rate, defined as absence of macroscopic or microscopic residual disease (locally/regionally/distantly) at radiological examinations, tissue and liquid biopsy, during non-operative management without salvage gastrectomy. The ongoing INFINITY proof-of-concept study may provide evidence on immunotherapy and the potential omission of surgery in localized/locally advanced GC/GEJC patients selected for dMMR/MSI-high status eligible for radical resection.

Success rate of microsatellite instability examination and complete response with pembrolizumab in biliary tract cancer.

Background and AimThe success rate of microsatellite instability (MSI) examination in biliary tract cancer (BTC) and the treatment outcomes of pembrolizumab in patients with MSI‐high (MSI‐H) BTC have not been fully investigated. We examined the success rate of MSI examination and the rate of MSI‐H status in patients with BTC as well as the treatment outcomes of patients with MSI‐H status who underwent pembrolizumab treatment.MethodsWe retrospectively reviewed 60 consecutive patients with unresectable or postoperative recurrent BTC who underwent MSI examination in a Japanese cancer referral center between January 2019 and September 2020.ResultsThe study included 24 intrahepatic cholangiocarcinomas, 12 hilar cholangiocarcinomas, 4 distal cholangiocarcinomas, 16 gallbladder carcinomas, and 4 ampullary carcinomas. The methods of cancer tissue sampling were percutaneous liver tumor biopsy in 26 cases, surgery in 15 cases, endoscopic ultrasound fine‐needle aspiration in 12 cases, transpapillary bile duct biopsy in 5 cases, and others in 2 cases. The success rate of MSI examination was 98.3% (59 of 60). MSI examination failed in only one case using a surgical specimen due to time‐dependent degradation of DNA. The frequency of MSI‐H BTC was 3.3% (2 of 60 cases). One patient with MSI‐H intrahepatic cholangiocarcinoma achieved a complete response with pembrolizumab treatment.ConclusionsMSI examinations in BTC were successful in almost all cases, regardless of tissue sampling methods. We experienced a case in which pembrolizumab resulted in a complete response to MSI‐H BTC. Since pembrolizumab for MSI‐H BTC could prolong survival time, MSI examination should be performed proactively to increase treatment options.

The genomic landscape of Chinese patients with upper tract urothelial carcinoma.

e16583 Background: Upper tract urothelial carcinoma (UTUC) is known to have a distinct aggressive clinical phenotype and its genomic characterization is poorly understood, especially in Asian population. In this study, we aimed to characterize the genomic landscape of Chinese UTUC patients and explore the clinical relevance, which is the largest cohort of UTUC to date. Methods: Overall, 122 Chinese patients with UTUC were enrolled. Tumor and germline DNA from patients were analyzed using a targeted next-generation sequencing assay to identify somatic mutations in 520 cancer associated genes. Mutations like deletion, amplification and gene fusion were included. Tumor mutational burden (TMB) and microsatellite instability (MSI) status were also evaluated. The frequency of genomic alterations in patients with UTUC was compared with that of the Western counterpart from previous studies. Results: In total, 13 low-grade and 109 high-grade UTUC patients were included in this study. The most frequent genomic alterations were identified in genes like TERT (50.0%; 61.5% low-grade vs 48.6% high-grade), KMT2D (48.4%; 61.5% vs 46.8%), FGFR3 (41.0%; 69.2% vs 37.6%), TP53 (37.7%; 7.7% vs 41.3%), CDKN2A (22.1%; 23.1% vs 22.0%), KDM6A (20.5%; 15.4% vs 21.1%) with different mutation frequencies in the two subgroups of patients. Despite the overall similarity (including FGFR3, ARID1A and CDKN2A), the comparison between our cohort and the two Western UTUC cohorts (n = 119, 24 low-grade and 95 high-grade) revealed significant differences in mutation frequencies of KMT2D (48.4% vs 36.1%), TERT (50.0% vs 26.9%), TP53 (37.7% vs 21.9%) and KDM6A (20.5% vs 32.8%) . Chi-square analysis revealed that patients with history of other cancers (4/17 vs. 3/105, P = 0.001) were more likely to have a MSI-high status. In addition, females (9/44 vs. 6/78, P = 0.039) and patients with cancer history (6/17 vs. 9/105, P = 0.002) were more likely to have high TMB (≥20 mutations/Mb; median: 6.48 mutations/Mb). At last, the frequency of germline P/LP variants were also similar but different in the spectrum between our cohort and the Western UTUC population. Differences in mutation frequency of APC (0 vs 2.6%), BRAC2 (2.6% vs 0.9%), CHEK2 (0.3% vs 1.8%), MSH2 (2.6% vs 5.3%) and MSH6 (0 vs 1.8%) were significant. Conclusions: This study revealed that Chinese UTUC patients had a similar frequency of genomic alterations with western patients. However, there were significant differences in the prevalence of several mutated genes including KMT2D, TERT, TP53 and KDM6A, suggesting the ethnicity differences between the two populations. Our findings laid the foundation of a deeper understanding of UTUC biology and will provide potential targets for the development of precision therapies in UTUC.

Clinical relevance of clonal hematopoiesis in metastatic gastrointestinal malignancies.

e16082 Background: Clonal hematopoiesis (CH) represents non-random clonal selection of bone marrow-derived cells marked by somatic mutations in certain genes. The presence of CH is associated with development of atherosclerosis and leukemia, and accelerated by toxic exposures (chemotherapy, radiation, smoking) and aging (Jaiswal et al. NEJM 2017; Abelson et al. Nature 2018). The impact of these genetic alterations on cellular function is unknown, especially in the broader context of immunity and in response to cancer therapy. To determine the contribution of CH to therapeutic response and hematologic toxicity in cancer patients, we examined the outcomes of patients treated with cytotoxic and immunotherapy in relationship to CH status. Methods: We evaluated patients with metastatic colorectal cancer (CRC) or esophagogastric cancer (EGC). DNA extracted from whole blood and tumor tissue were sequenced in tandem as part of the MSK-IMPACT hybridization capture-based sequencing assay. CH was defined as any mutation with a VAF of at least 2%, present in at least 10 reads, with at least 2:1 blood:tumor reads, or 1.5:1 blood:lymph node that was not found in gnomAD with a frequency &gt; 0.005. Additional filtering and putative driver definitions (CH-PD) were described by Bolton et al. Nature Genetics 2020. Multivariate survival analyses were performed using a Cox Proportional Hazard model correcting for CH, CH-PD, prior smoking, prior chemotherapy, prior radiation, MSI status, and age at cancer diagnosis. Results: 654 patients with EGC (n = 348) and CRC (n = 306) who began treatment between 2006 and 2020 were included in the analysis. CH was present in 34.5% and 24.4% of each group, and 17.2% and 12.9% harbored CH-PD, respectively. CH and CH-PD were both associated with older age and smoking history, and CH was also associated with prior radiation and MSI-high status (p &lt; 0.05). Patients with CH or CH-PD receiving first-line (1L) therapy for CRC or EGC demonstrated no difference in mPFS after multivariate analysis, though 1L EGC patients with CH-PD had inferior mOS (p = 9e-5). There was no difference in pre-1L WBC, ANC, or ALC, nor in G-CSF or PEG-G-CSF doses administered during 1L therapy between patients with CH or CH-PD versus those without. Similarly, presence of CH or CH-PD had no impact on mPFS or mOS in patients receiving immune checkpoint blockade (ICB) without concurrent chemotherapy after multivariate survival analysis. Conclusions: We confirmed that the mere presence of CH is not prognostic for overall survival, but that EGC patients with CH-PD mutations have inferior overall survival, which is consistent with previous findings. Presence of CH or CH-PD was not associated with differences in baseline leukocyte counts nor need for G-CSF support, nor did it impact PFS in either tumor type, suggesting limited utility of CH in solid tumor clinical decision-making.