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The association of antibiotic use and survival among patients receiving first line immunotherapy-based treatment for advanced gastroesophageal cancers.

349 Background: The advent of immune checkpoint inhibition (ICI) has improved the survival for patients with gastroesophageal cancer (GEC). It is vital to understand the relationship between the tumor microenvironment and the ability of the immune system to prevent and eliminate cancer cells. Antibiotics (abx), frequently used in patients on cancer-directed therapy, can alter gut microbiota leading to dysbiosis and altered immune responses. Some research shows its use is associated with decreased ICI efficacy in RCC, NSCLC, and melanoma. The goal of our study is to investigate the association of abx timing and survival with 1L ICI-based treatments for advanced GEC. Methods: The retrospective, multicenter analysis used the Flatiron Health deidentified electronic health record-derived database of real world (rw) patients with advanced esophageal, GEJ, and gastric cancers (EC/GEJC/GC) who received ICI +/- chemotherapy (chemo) as 1L therapy. Abx exposure was defined by antibiotic use from 42 days before to 42 days after starting ICI. The cox proportion hazards models were used to compare rw overall survival (OS) and progression-free survival (PFS) across exposure groups. Results: A total of 990 patients were included for the main group analysis with comparison of survival and abx usage and timing: 876 did not receive abx, 58 received abx within 42 days after starting ICI, and 56 received abx within 42 days prior to starting ICI. The median age was 66 with 44.4% EC, 33.5% GC, and 22% GEJC. The majority of patients had adenocarcinoma (87.9%). The unadjusted OS HR for abx (within 42 days) before ICI was 0.99 (0.68-1.46, p=0.971) and (within 42 days) after ICI was 1.56 (1.11-2.19, p=0.011), suggesting worse OS with abx use after ICI initiation. HR trended towards worse PFS for those receiving abx after 1L ICI [1.36 (0.97-1.90 p= 0.073)]. In subgroup analysis, the negative effect of starting abx after 1L ICI over abx before ICI was more prominent in those receiving ICI monotherapy compared to those receiving chemo/ICI. Conclusions: Our study identifies a poorer survival association of abx administration after 1L ICI-based therapy for advanced GEC, primarily driven by ICI monotherapy. Main group comparison between abx usage and timing: OS Abx Use/Timing n (%) HR No 876 (88.5) Yes, after 1L IO 58 (5.9) 1.56 (1.11-2.19, p=0.011) Yes, before 1L IO 56 (5.7) 0.99 (0.68-1.46, p=0.971) Subgroup comparison between abx usage and timing by treatment type Chemo + IO: OS Yes, after 1L IO 44 (6.9) 1.32 (0.88-1.98,p=0.177) Yes, before 1L IO 38 (6.0) 1.01 (0.62-1.65, p=0.964) IO monotherapy: OS Yes, after 1L IO 12 (4.9) 2.64 (1.38-5.06, p=0.003) Yes, before 1L IO 12 (4.9) 1.09 (0.53-2.23, p=0.810)

Conformational transitions of Streptococcus pyogenes Cas9 induced by salt and single-guide RNA binding

A phase I/II clinical trial of preoperative docetaxel/oxaliplatin/S-1 (DOS) combination therapy for esophagogastric junction adenocarcinoma.

429 Background: Esophagogastric junction (EGJ) cancer is difficult to cure with surgery alone, necessitating adjuvant chemotherapy. However, administering aggressive adjuvant chemotherapy after invasive surgery is difficult. Neoadjuvant chemotherapy, on the other hand, is expected to enhance compliance, increase the rate of curative resection, and reduce recurrence. Methods: We conducted a single center Phase I/II study to evaluate the safety and efficacy of neoadjuvant chemotherapy using docetaxel, oxaliplatin, and S-1 (DOS), followed by adjuvant chemotherapy with S-1 in patients with cT3-4aN0-3M0 adenocarcinoma of the EGJ. In Phase I, we estimated the maximum tolerated dose and dose-limiting toxicity of neoadjuvant DOS therapy and determined the recommended dose (RD). In Phase II, we assessed the safety and efficacy of the RD established in Phase I. The primary endpoint was the curative resection rate, with secondary endpoints including the 3-year overall survival rate, 3-year recurrence-free survival rate, treatment completion rate, response rate to neoadjuvant chemotherapy, pathological response, and adverse events. Neoadjuvant DOS chemotherapy was administered in three 3-week cycles. The starting dose of docetaxel was 50 mg/m², with plans to escalate it to 60 mg/m². Docetaxel and oxaliplatin (100 mg/m²) were administered on day 1, while S-1 (120 mg/body) was given orally on days 1-14. Postoperative adjuvant chemotherapy consisted of S-1 (120 mg/body), administered for 4 weeks followed by a 2-week rest period, repeated for 8 cycles. Results: Based on the 6 patients enrolled in Phase I, the RD of docetaxel was determined to be 60 mg/m². A total of 40 eligible patients, including 3 from Phase I, were enrolled in the study. Two patients discontinued protocol treatment during neoadjuvant chemotherapy due to adverse events and 1 patient discontinued due to positive peritoneal cytology. The R0 resection rate was 87.5% (35/40). Surgical procedures included esophagectomy in 18 patients, total gastrectomy in 15, and proximal gastrectomy in 4. Postoperative complications of Grade III or higher, as per the Clavien-Dindo classification, occurred in 15.0% of patients, with no surgery-related deaths. The response rates to neoadjuvant chemotherapy were 12.5% for PR, 2.5% for PD, and 85.0% for non-CR/non-PD. Pathological response rates were: Grade III in 8.1%, Grade II in 35.1% and Grade I in 56.8%. During neoadjuvant chemotherapy, Grade 3 or higher adverse events were observed, including neutropenia (82.5%), nausea (5%) and diarrhea (5%). The neoadjuvant chemotherapy completion rate was 92.5%, although 59.5% of patients required dose reductions. Conclusions: Neoadjuvant DOS therapy for esophagogastric junction cancer shows promise, achieving a high R0 resection rate and substantial pathological efficacy, with acceptable levels of adverse events. Clinical trial information: UMIN000022210.

Correlation of mid-chemoradiation ctDNA results and clinical complete response to total neoadjuvant therapy (TNT) for locally advanced rectal adenocarcinoma.

263 Background: The total neoadjuvant therapy (TNT) paradigm for locally advanced rectal cancer (LARC) is evolving with intensification and de-escalation neoadjuvant therapies. Chemoradiation (CRT) followed by consolidation chemotherapy offers the highest rate of organ preservation. Circulating tumor DNA (ctDNA) response during TNT may serve as a biomarker that allows for therapy personalization to better select candidates for rectal organ preservation (Watch-and-Wait, WW). Methods: We enrolled patients with mismatch repair proficient LARC eligible for TNT on a prospective protocol (NCT05108428). Patients underwent CRT to 50.4 Gy with a mid-treatment evaluation (27 Gy) on a MRI-linac followed by 8 cycles of consolidation FOLFOX. A sequential MRI-guided adaptive radiotherapy boost to 59.4 Gy was delivered if rectal tumor volume reduced > 30% at 27 Gy. Standard restaging with diagnostic MRI and endoscopy occurred after TNT to evaluate organ preservation candidacy. ctDNA was obtained at diagnosis, mid-CRT (27 Gy), completion of TNT, and regular intervals in surveillance. ctDNA analysis was performed using a clinically validated, personalized, tumor-informed assay (Signatera, Natera, Inc.). Descriptive statistics for clinical response for mid-treatment assessment are reported. Additional clinical outcomes will be reported as follow up matures. Results: A total of 20 patients were enrolled (70% male, 70% cN+) with average age of 58 (range: 30-86) and 40% with threatened or involved radial margin. Average follow up is 12 months (range: 4-24 months) from date of completion of TNT. Average initial tumor volume was 26cc (range: 8.6cc- 66.8cc) with an average tumor reduction of 68.5% at 27 Gy. Volumetric change based on mid treatment MRI >30% did not predict WW eligibility (2 patients with <30% volumetric change maintains clinical complete responses). All patients demonstrated positive ctDNA at diagnosis (average 7.08 MTM/mL, range: 0.08 MTM/mL -77.96 MTM/mL). 25% of patients had elevated CEA at diagnosis. Conversion to negative ctDNA at mid-CRT occurred in 53% of patients. 57% of patients with a positive ctDNA at this timepoint underwent formal oncologic mesorectal excision with adenocarcinoma confirmed in the specimens. 25% of patients with negative ctDNA at this timepoint underwent a local excision, with no histologic invasive cancer in both specimens. We observed a 100% rectal organ preservation rate when early conversion to negative ctDNA at the 27 Gy of CRT timepoint. Conclusions: ctDNA clearance during CRT may be a good early predictor for patients that may be a candidate for a WW protocol. This biomarker may also guide consolidation therapy escalation (FOLFIRINOX) or de-escalation (chemotherapy omission) for select patients. Longer follow up is needed to correlate with clinical outcomes and future studies with more patients is needed. Clinical trial information: NCT05108428 .

MEK inhibitor-based therapy in metastatic pancreatic adenocarcinoma with <i>KRAS</i> G12D or <i>KRAS</i> G12V alteration.

726 Background: Up to 95% of pancreatic ductal adenocarcinomas (PDAC) are driven by oncogenic alterations in the KRAS gene, with KRAS G12D (40%) and KRAS G12V (30%) mutations being the most common. However, in most cases, KRAS alterations are accompanied by alterations in other tumor suppressors such as TP53 , CDKN2A/B , and SMAD4 . Therefore, targeting KRAS alone may not be sufficient for effective treatment of PDAC . As part of the MCW-Master-PREDICT (NCT05802069) observational study, we evaluated the effectiveness of MEK inhibitor (MEK-inh)-based therapy, tailored to the unique molecular alterations of each patient’s tumor, in treating metastatic PDAC (mPDAC) with KRAS G12D or KRAS G12V alterations. Methods: From April 2022 to December 2023, 19 patients ( KRAS G12D=10 (53%), KRAS G12V=9 (47%)) were treated with MEK-inh-based therapy. Comprehensive genomic profiling was performed using Tempus xT (648 genes) in 15 patients (79%), FoundationOne (324 genes) in 4 patients (21%), and STRATA (429 genes) in 1 patient. The genomic characteristics, matched therapies, and treatment outcomes are provided (Table). Results: Of the 19 patients, 11 (58%) were female. The median age at the initiation of MEK-inh-based therapy was 67 years. Six (32%) patients received MEK-inh-based therapy as first or second-line treatment, while 13 (68%) patients were treated in the third to fifth-line. Among the 19 patients, the median overall survival (mOS) and median progression-free survival (mPFS) from the initiation of MEK-inh-based therapy were 5 and 2 months, respectively. The mOS from the time of MEK-inh-based therapy was 5.1 months for KRAS G12D, and 4.7 months for KRAS G12V (P=0.87). The mPFS from the time of MEK-inh-based therapy was 2.3 months for KRAS G12D and 1.4 months for KRAS G12V (P=0.12). Among all 19 patients, 4 (21%) patients had mPFS above 4 months ( KRAS G12V=1, KRAS G12D=3; 4.1, 4.3, 4.7, 9.9 months). Conclusions: The efficacy of MEK-inh-based therapy was limited in the late-line treatment of mPDAC for patients with KRAS G12D and KRAS G12V mutations. The potential role of MEK inhibitors in earlier lines of therapy, and their combination with KRAS inhibitors, requires further prospective evaluation. Tumor alterations and matched therapies. Altered gene KRAS G12V(N=9) KRAS G12D(N=10) Patients matched(N=19) Type of matched therapy KRAS G12D/V 9 (100%) 10 (100%) 19 (100%) MEK inhibitor TP53 7 (78%) 8 (80%) 8 (42%) VEGF/VEGR inhibitor* CDKN2A/B 8 (89%) 5 (50%) 9 (47%) CDK4/6 inhibitor** SMAD4 3 (33%) 4 (40%) 4 (21%) MEK inhibitor + (EGFR or pan-HER inhibitor) *** *PMID: 27466356; **PMID: 33472910; ***PMID: 36127339, PMID: 24625091. N= number of patients.

Modified Frailty Index (mFI-5) as a prognostic tool of mortality, complications, and readmissions in patients undergoing hepatic ablation for hepatocellular carcinoma.

610 Background: Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths, often diagnosed late, limiting curative options. Transarterial chemoembolization, Y-90 radioablation, radiofrequency ablation, and thermoablation are commonly used for downstaging, transplant bridging, and palliation in unresectable HCC. Frailty, linked to postoperative complications, has not been studied in hepatic ablation patients. This study evaluates the predictive value of the modified frailty index (mFI-5) for mortality, readmissions, complications, redo procedures, and discharges. Methods: We utilized the National Surgical Quality Improvement Program (NSQIP) database from 2015 to 2019, querying cases of hepatic ablation for CPT codes: 47370 (closed hepatic ablation, single site) and 47380 (open hepatic ablation, single site). Selected cases were analyzed for frailty using the mFI-5 criteria. A multivariate analysis was performed using mFI-5 frailty scores, stratified into non-frail (0), pre-frail (1), frail (2), and severely frail (3+). The outcomes analyzed included mortality, discharge to a destination other than home, major complications, minor complications, readmission, and reoperation. Results: We identified 1921 patients as: 737 non-frail, 701 pre-frail, 442 frail and 41 severely frail. The rates of readmission (5.4%), reoperation (1.4%), major (5.3%) and minor (3.5%) complications were low. Eight patients died following hepatic ablation, and 79 patients were discharged to a destination other than home. In multivariate analysis, most outcomes were not significantly associated with increasing frailty. However, discharge to a destination other than home was significantly more likely in patients with higher frailty scores. In frail patients, the odds ratio (OR) was 2.325 (95% CI 1.228–4.402), and in severely frail patients, this increased to 8.720 (95% CI 3.389–22.435). Conclusions: Hepatic ablation is generally well tolerated with low complication rates; however, frailty significantly influences postoperative outcomes. Frail and severely frail patients are more likely to be discharged to care facilities rather than returning home, suggesting that even in the absence of major complications, these patients require a higher level of post-procedural care. This underscores the need for tailored discharge planning and resource allocation based on patient frailty.

P300/RNA polymerase II mediates induction of the teleost viral RNA sensor MDA5 through the interferon regulatory factor IRF11

Vascular endothelial growth factor receptor (VEGFR) -tyrosine kinase inhibitors combined with programmed death receptor-1 (PD-1) inhibitors as third- or later-line treatment in patients with microsatellite-stable (MSS) metastatic colorectal cancer (mCRC): A retrospective study.

68 Background: Microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) shows a low response to programmed death receptor-1 (PD-1) inhibitors. Recent studies suggest that combining vascular endothelial growth factor receptor (VEGFR)-tyrosine kinase inhibitors (TKIs) with PD-1 inhibitors may enhance the anti-cancer activity for mCRC patients. Multiple antiangiogenic drugs have been approved by the FDA and NMPA for the treatment of later-line mCRC. Nevertheless, the effects of various anti-angiogenic drugs when used in combination with immunotherapy for mCRC treatment is not yet fully established. Methods: We conducted a non-interventional, retrospective study. Data were compiled from patients with mCRC at Shandong Cancer Hospital. Eligible patients must have received a combination of anti-angiogenic drugs and PD-1 inhibitors following at least two lines of standard treatment. The treatment period spanned from August 2019 to April 2024. The primary endpoint was overall survival (OS), and the secondary endpoint was progression-free survival (PFS). Results: At the cut-off date (April 29th, 2024), 79 eligible patients were available for analysis. Of these, 49 patients received fruquintinib in combination with PD-1 inhibitors (F group), 30 patients received investigator-selected other anti-angiogenic agents in combination with PD-1 inhibitors (NF group). The baseline characteristics of the two groups were well balanced. The median overall survival (OS) was significantly longer in the F group compared to the NF group (hazard ratio [HR]: 0.36, 95% CI 0.14-0.96, P=0.042). The median OS was not reached (95% CI 21.1-NA) in the F group, whereas it was 19.1 months (95% CI 12.6-NA) in the NF group. Subgroup analyses of OS were generally consistent with benefit in the whole population across nearly all subgroups. In contrast to NF group, individuals in F group demonstrated a significant enhancement in overall survival (OS) when patients had received prior bevacizumab (HR: 0.26, 95% CI 0.07-0.75, P=0.015), had no prior treatment with cetuximab (HR: 0.23, 95% CI 0.26-0.97, P=0.045), or had experienced surgical resection at baseline (HR: 0.34, 95% CI 0.12-0.95, P=0.041). The median PFS between two groups showed no statistically significant difference (HR: 0.65, 95% CI 0.38-1.13, P=0.127), F group 6.1 months (95% CI 4.6-10.3) versus NF group 4.4 months (95% CI, 3.0-7.5). Conclusions: Fruquintinib demonstrated improved OS over other anti-angiogenic agents when combined with immunotherapy for third or later-line MSS mCRC treatment.

Short-course radiotherapy (SCRT) followed by fruquintinib plus adebrelimab and CAPOX in the total neoadjuvant therapy of locally advanced rectal cancer (LARC): A multicenter, single-arm, open-label, phase II study (UNION TNT).

192 Background: We have demonstrated that neoadjuvant SCRT followed by PD-1 inhibitor plus CAPOX for LARC patients (pts) showed a higher pCR rate and a well-tolerated safety profile in phase III UNION study. Fruquintinib is a potent and highly selective VEGFR inhibitor, which had been approved for previously treated mCRC pts. This study aimed to investigate the efficacy and safety of SCRT followed by fruquintinib plus adebrelimab and CAPOX as a total neoadjuvant therapy for high-risk LARC pts. Methods: In this prospective, open-label, multi-centers, single-arm phase 2 study (NCT06234007), pts diagnosed with newly diagnosed and high risk LARC were recruited. Pts received SCRT (25Gy/5f) followed by six cycles of fruquintinib (4mg, qd, po, q3w,for the initial 6 pts in the safety run-in period, dosage would be adjusted based on dose-limited toxicities in the 1st cycle) combined with adebrelimab (1200mg, iv, d1, q3w) and CAPOX (q3w). Primary endpoint was CR rate (including clinical CR &amp; pathologic CR). Secondary endpoints included 3-year EFS rate, OS, R0 resection rate and safety. Results: As of 30 Aug 2024, 45 pts were enrolled (median age 59 years [range: 24-75], 26 males, 23 clinical T4 stage and 20 clinical N2 stage, 36 with EMVI positive, 31 with MRF positive, 22 tumor located ≤5cm from the anal verge). Up to 20 Sep 2024, all pts completed SCRT, 73.33% (33/45), 57.78% (26/45) and 31.11% (14/45) pts completed two, four and six cycles of combination therapy, respectively. At data cut-off, of 33 pts included in the efficacy analysis, 28 pts underwent MRI examination and mrTRG results were available, the remaining 5 pts had early surgery due to AEs/serious AEs. 35.7% (10/28) and 46.43% (13/28) pts were classified as mrTRG1 and mrTRG2, respectively. Of 19 pts who underwent surgery, R0 rate was achieved in all 19 pts (100%) and pCR was achieved in 12 pts (63.16%). Moreover, 1 pt achieved cCR during neoadjuvant therapy, thus the treatment strategy provided a CR rate of 65% (1 cCR plus 12 pCR divided by 20). Grade 3/4 adverse effects (AEs) occurred in 16 pts (47.06%), and most commonly were lymphocyte count decreased (n=6, 18.18%), diarrhea (n=5, 15.15%) and AST increased (n=2, 6.06%). 4 serious AEs reported with intestinal perforation and all achieved pCR after surgery therapy. No treatment related death was reported. Conclusions: SCRT followed by fruquintinib combined with adebrelimab and CAPOX as a total neoadjuvant therapy showed promising CR rate and favorable pCR for high-risk LARC pts, and the safety profile was generally manageable. This treatment strategy might be a potential option as neoadjuvant therapy for high-risk LARC pts. Updated data will be presented in the future. Clinical trial information: NCT06234007 .

Incidence trends, demographic disparities, and survival outcomes of gastrointestinal malignancies in young adults: A focus on stomach and pancreatic cancers.

339 Background: The incidence of gastrointestinal (GI) cancers has been rising among younger populations. While prior research has highlighted the increasing incidence of colorectal cancer (CRC) in adolescents and young adults (AYA), defined as individuals aged 15-39, there is less focus on non-CRC GI malignancies, such as stomach and pancreatic cancers, within this age group. This study aims to further elucidate the incidence, mortality, and demographic disparities in the AYA population for stomach and pancreatic cancers compared to older populations (&gt;50 years old). Methods: Data was extracted from the SEER database spanning from 2000 to 2020. Demographic, clinical, and secondary cancer characteristics were summarized across the sample, stratified by cancer type. Overall survival (OS) and disease-specific survival (DSS) were analyzed using the Kaplan-Meier method, with comparisons performed via the log-rank test. Univariate and multivariate analyses were conducted to identify predictors of survival outcomes. Results: We identified 19,983 AYA patients diagnosed with non-CRC GI malignancies (including esophageal, stomach, small intestine, anal, hepatobiliary, and pancreatic cancers) between 2000 and 2020. Among these patients, the majority were male (58%), White (47%), and resided in metropolitan areas (90%). The median age at diagnosis was 38 years. Pancreatic cancer was 20% more common in the AYA group compared to those over 50 years old (12%), while stomach cancer was also more prevalent in the AYA group (27% vs. 17%). Survival outcomes were significantly better in the AYA group, with a median OS of 24 months compared to 9 months in the older population, and a median DSS of 52 months versus 13 months (p&lt;0.001). Predictors of worse OS and DSS included male sex, African American race, income below $45,000/year, lack of surgical intervention, and delayed initiation of treatment. Conclusions: The incidence of stomach and pancreatic cancers is notably higher in the AYA population compared to older adults, with AYA patients demonstrating better overall and disease-specific survival outcomes. However, certain demographic factors, such as male sex, African American race, and lower income, are associated with worse survival, underscoring the need for targeted interventions to address these disparities. Early diagnosis and timely treatment are critical to improving outcomes in this younger population.

Tumour-free ctDNA detection as a decision tool to support organ preservation in node-negative rectal cancer undergoing neoadjuvant chemotherapy, excision, and observation in the phase II NEO trial (CCTG CO.28).

20 Background: In the NEO trial (CCTG CO.28, NCT03259035) patients with node negative (N0) T1-T3 rectal cancer were treated with neoadjuvant CAPOX/FOLFOX and transanal excision surgery (TES) with the goal of organ preservation. Patients without documented response following neoadjuvant chemotherapy were recommended total mesorectal excision (TME). We present a post-hoc assessment of ctDNA detection in this early-stage population and correlate kinetics with response and outcomes. Methods: Fifty-eight patients enrolled in CO.28. Whole blood was collected in EDTA tubes and processed for future ctDNA analysis at up to six timepoints: pre-chemotherapy, after neoadjuvant chemotherapy (and pre-TES), yearly during surveillance for 3 years and upon progression. A total of 195 samples were analyzed with the Guardant Reveal™ assay: a tissue-free epigenomic assay leveraging &gt;20,000 epigenomic regions for ctDNA detection. Results: Of 48 available pre-treatment samples, ctDNA was detected in 22 (46%). Sensitivity by T-stage was 14% (1/7) for T1, 53% (17/32) for T2, 44% (4/9) for T3 cancers. ctDNA detection was lower following neoadjuvant chemotherapy (4/46, 9%, p&lt;0.001 vs pre-chemotherapy). Of 41 patients with paired pre- and post-chemo samples, 49% (20/41) had undetectable ctDNA at both timepoints, 44% (18/41) had reduced tumour fraction following chemotherapy, the majority of which completely cleared ctDNA (94%; 17/18) and 7% (3/41) had an increased tumour fraction following chemotherapy (67%, 2/3 changing from negative to positive), all three of whom failed to respond to neoadjuvant chemotherapy and had TME recommended (100%). In contrast, of those that cleared ctDNA following chemotherapy, 35% had TME recommended (6/17, p=0.074). Of five recurrences (3 distant, 2 local), all had negative or reduced ctDNA tumour fraction during neoadjuvant therapy before surgical intervention. Among patients with local relapse who were managed with TES, 1/2 (50%) had detectable ctDNA at the time of local progression. No samples were available for those with distant recurrences (3/5) at time of relapse. Conclusions: The Guardant Reveal tissue-free assay was able to detect ctDNA even in this extremely early-stage cohort and identified cancers with inadequate response to therapy and in whom TME was recommended. A tissue-free approach may support timeliness of ctDNA results that would support ctDNA as an additional decision tool with endoscopic and MRI assessments to increase physician and patient comfort with organ preservation. Clinical trial information: 03259035.

Diet-induced obesity mediated through estrogen-related receptor α is independent of intestinal function

Biomarkers associated with recurrence after salvage surgery for localized anal cancer (AC).

9 Background: While most patients with localized AC are cured by chemoradiation (cRT), some recur and require salvage surgery (SS). No adjuvant therapies are effective after SS. We profiled cRT-refractory AC tumors from SS to identify biomarkers linked to recurrence. Methods: Using an IRB-approved protocol, patients with localized, cRT-refractory AC were classified as recurrent (R; N=19) or non-recurrent (NR; N=10) according to outcome after SS. Digital spatial profiling whole transcriptome analysis (GeoMx) on FFPE AC evaluated expression of 18000+ genes on 40 regions of interest (ROI) for R vs 25 ROIs for NR AC cores, separated into “tumor” (panCK+) and “tumor microenvironment” (TME; panCK-). log2 transformed RNA counts were compared for expression between ROIs of R and NR AC (limma). For GSEA hallmark pathway analysis, normalized enrichment scores (NES) were calculated using genes with differential gene expression. Expression of immune biomarkers using multiplex immunofluorescence (mIF) were quantified (N/mm2) and compared with a student’s t-test. Results: With a median follow up of 26.6 months, median OS (29.1 months vs NR; p&lt; .001) was shorter for R AC. For NR AC, higher expression of genes associated with immune activation (p-adj&lt; .0001 for all) - B2M (fold change (FC) 33.0), HLA-DPA1 (FC 30.1), and HLA-DPB1 (FC 15.0) – and higher NES for “interferon alpha response” (NES 3.2) and “interferon gamma response” (NES 3.1) (FDR &lt; .05 for both) were observed. R AC had higher expression of genes (p-adj &lt; .0001 for all) regulating TGF-beta signaling – LY6K (FC 10.3) and BCAR3 (FC 3.6), and higher “EMT” (NES 2.1) and “TGF-beta” (NES 1.6) GSEA signatures (FDR&lt; .05 for both). On mIF, greater CD3+CD8+ T cells were observed in tumor (148 vs 42 N/mm2; p=.02) and TME (8.2 vs 2.8 N/mm2; p=.008) for NR AC. Increased Thy1+ cancer-associated fibroblasts were noted in tumor (4.2 vs 1.2 N/mm2; p=.04) and in TME (149 vs 69 N/mm2; p=.04) for R AC. Conclusions: Signatures of immune activation were observed with gene expression and mIF in AC patients cured by SS. R AC had higher immune suppressing profiles. These data support developing novel therapeutics that promote immune activation in trials of patients with cRT-refractory AC at high risk for recurrence after SS.

Adverse events (AEs) –derived biomarker in predicting clinical outcomes in patients with colorectal cancer (CRC) treated with immunotherapy (IC).

132 Background: There are insufficient studies evaluating the role of AEs in CRC patients treated with IC. This study aims to transform AEs from traditional toxicity evaluation tools to informative biomarkers for assessing treatment efficacy by utilizing modern analytical strategies. Methods: We analyzed a single arm study of 51 mismatch repair proficient, refractory CRC patients (NCT03712943) treated with regorafenib and nivolumab. Data for analysis included CTCAE version 5 AE data, RECIST treatment response, progression-free survival (PFS), and overall survival (OS). Analytic approach leveraged multiple AE parameters to develop a set of innovative AE biomarkers. One AE biomarker of interest was treatment related low-grade early AEs (TR-LG-AE) which was defined as frequency of all TR-LG-AEs occurring between the 1st day and day 30 after the 1st treatment. Results: TR-LG-AE was associated with treatment response (p&lt;0.001 by ANOVA trend test). Patients with higher AE events tended to be a responder, compared to PD patients with a lower frequency of AE events. The TR-LG-AE also correlated with improved PFS and OS with hazard ratio of 0.83 (p=0.01) and 0.89 (p=0.03), respectively. Accordingly, patients were grouped into high versus low TR-LG-AE based on optimal cutoff of 6 events for further analysis. The dichotomized TR-LG-AE (high vs low) showed significant association with survival outcomes (median PFS: 15.3 vs 3.7 months; p&lt;0.001; median OS: 21.9 vs 9 months; p=0.02). Further interaction analysis showed patients with high TR-LG-AE had improved PFS regardless of occurrence of high-grade AE (HG-AE) (p=0.01), suggesting its independence of HG-AE. Individual AE analysis identified patients experienced with early low-grade rash maculo-papular, lipase increased, or hypertension had improved PFS (p&lt;0.001). In biomarker analysis, one key mutation biomarker, RAS, did not show significant association with survival outcomes (PFS: p=0.66; OS: p=0.81). In contrast, integration with TR-LG-AE led to remarkable improvement. Specifically, the TR-LG-AE was able to help improve RAS classification by identifying patients with better treatment benefit. Specifically, patients with RAS mutation and high TR-LG-AE experiences had a median PFS of 15.3 months compared to others (median PFS of 3.7 months; p=0.007), and a median OS of 21.9 months compared to others (median OS of 9.4 months; p=0.04). Conclusions: The study demonstrated utility of AE in predicting clinical outcomes in CRC, similar to our previous findings in lung cancer. Moreover, it discovered that integration of AE-derived biomarkers with molecular biomarkers could produce a more robust classifier than when considered individually. This analysis is the first of its kind to identify subgroups of CRC patients that benefit from IC treatment.

Dose-escalated radiation for locally advanced unresectable pancreatic cancer.

750 Background: Patients with unresectable locally advanced pancreatic cancer have limited therapeutic options. Historical treatments have included systemic chemotherapy or palliative radiation. New advanced radiotherapy treatment techniques have allowed dose escalated ablative radiotherapy to be delivered for patients with cancer limited to the pancreas. This study retrospectively reviews the long term outcomes of patients receiving dose escalated radiation for unresectable localized pancreatic cancer. Methods: Patients with locally advanced unresectable pancreatic underwent neoadjuvant chemotherapy with either gemcitabine or FOLFIRINOX based regimens. When maximum response was achieved with chemotherapy or this was no longer tolerated, patients were reassessed with imaging. Patients with localized unresectable disease then proceeded to definitive dose escalated radiation with either SBRT radiosurgery (40Gy in 5 fractions) or IMRT radiation (65-70Gy in 30-35 fractions) with concurrent 5FU. Surveillance of disease was performed with CT imaging and Ca19-9 biomarker assessment. Results: A total of 38 patients (21 male, 17 female) underwent definitive radiation. Radiation technique was determined by treating physician based on patient anatomy, with 7 patients having SBRT and 31 IMRT/5FU. Average patient age at diagnosis was 71. All patients underwent at least 6 months of follow up and mean follow up was 14 months. At time of latest follow up, 30 patients had no evidence of local progression and 12 patients had no evidence of progression at any site. The most common side effect at last follow up was grade 2/3 duodenal ulcer experienced by 7 patients. Conclusions: Advances in systemic chemotherapy have increased the population of patients with locally advanced unresectable pancreatic cancer who have persistent pancreatic disease after induction chemotherapy. Definitive dose escalated radiation is a new and effective technique to provide local control in this setting. This approach is well tolerated with manageable toxicity and effective durable local control. Patients continue to experience distant disease failure despite improving local control rates, though at a lower rate than historical controls. Control of primary pancreatic malignancy with dose escalated radiation can potentially improve quality of life and function for these patients for whom additional chemotherapy or surgery is not indicated.

Disparities in Allograft Access in the Era of Post-Transplant Cyclophosphamide-Based Mismatched Unrelated Donor Transplantation

Substrate adaptors are flexible tethering modules that enhance substrate methylation by the arginine methyltransferase PRMT5

Disparities and barriers in germline testing among patients with early-onset gastrointestinal cancers.

35 Background: Early-onset gastrointestinal cancers (EOGIC) are strongly associated with hereditary predisposition, making germline testing essential for treatment and familial risk management. Disparities in germline testing persist. This study investigates disparities and barriers to germline testing in EOGIC. Methods: This IRB-approved retrospective analysis included 864 patients aged 18-49 with GI cancers at the University of Chicago (2018-2023). Data collected included race, gender, age, insurance, family cancer history, and subtype. Outcomes were physician referrals for germline testing and completion. Chi-square tests and logistic regression models assessed predictors of recommendations and completion. Results: Of 864 patients, 473 (54.7%) received germline testing recommendations, and 323 (37.4%) completed testing. Completion rates: 30.2% for no insurance, 29.1% for Medicare/Medicaid, and 40.3% for private insurance (p=0.032). Patients with family history of cancer were more likely to be recommended for testing (62.9% vs. 39.5%, p&lt;0.001) and complete it (44.0% vs. 23.7%, p&lt;0.001). In our cohort, no significant racial disparities were observed (p=0.712 and p=0.358). Females were more likely to receive recommendations (59.1%) and complete testing (41.2%) than males (50.9% referral, 34.0% completion, p=0.016 and p=0.029). Patients under 30 had the highest rates of testing recommendation (66.1%) and completion (46.4%), followed by 30-39 (61.7%, 44.4%) and 40-49 (51.2%, 34.0%), p=0.006 and p=0.009. By cancer subtype, colorectal cancer (CRC) patients had the highest referral (66.1%) and completion (45.9%) rates, while anal cancer had the lowest (13.2% referral, 5.3% completion, OR 0.08, p&lt;0.0001). Gastric cancer (52.3% referral, 29.2% completion, OR 0.49, p=0.005) and esophageal cancer (36.9% referral, 20.0% completion, OR 0.31, p&lt;0.0001) also had lower testing rates. Liver cancer (35.4% referral, 27.1% completion, OR 0.38, p&lt;0.0001) and cholangiocarcinoma (45.5% referral, 22.7% completion, OR 0.28, p=0.016) showed similarly low rates. Conclusions: Disparities in germline testing were seen among uninsured patients, males, and those with public insurance. CRC had the highest testing rates, while anal, esophageal, liver, and cholangiocarcinoma had lower rates, likely due to lower suspicion of hereditary predisposition. Targeted interventions are needed to improve testing uptake and completion, especially among uninsured and underrepresented populations.

Clinical validation of the Northstar Response: A novel quantitative methylation ctDNA monitoring assay for advanced GI cancer treatment response.

839 Background: Circulating tumor DNA (ctDNA) is a promising tool for monitoring treatment response but is challenged by pan-cancer quantification and consistent outcome correlations. Northstar Response (NSR) quantifies &gt;500 cancer specific methylated loci, offering a reflection of disease burden and clinical response. Methods: We present a prospective observational study to evaluate the clinical utility of NSR. Patients with advanced GI cancers had serial ctDNA assessed at baseline and during systemic treatment with correlations to radiographic or clinical response. Tumor methylation scores (TMS) were expressed as Log10 values and a mixed-effects model evaluated clinical assessment correlations. Results: 73 patients with locally advanced or metastatic GI cancers were analyzed. Among these, 35 (47.9%) had at least four ctDNA assays and all had radiographic or clinical response assessments. The median age was 66 years (± 8.5), with most being male (67.1%) and White (74.0%). Table 1 shows the case distribution. Baseline TMS had significant variation (p=0.023), but was measurable across all tumor types. CRC exhibited the highest mean TMS-log10 while biliary and pancreatic cancers had the lowest. Cases with both primary and metastatic lesions had a higher mean TMS-log10 than cases with either primary tumors alone or metastatic lesions alone (3.4 vs. 3.0). Compared to stable and responsive disease, TMS changes correlated with progressive disease, with a coefficient of 0.48 at the third collection time point (p=0.05). However, 23/73 (32%) cases were without an on-treatment TMS timepoint (OTT) due to rapid progression (average time to death of 24 vs. 103 days for patients with OTT). In exploratory modeling of TMS relative to RECIST-like treatment response for those with OTT, NSR evaluations were associated with response assessments (p&lt;0.04, Fisher’s Exact Test). Conclusions: TMS was consistently measurable but varied across tumor types and correlated with disease burden. TMS changes appeared associated with response assessments when accounting for rapid progressors. Additional analyses are ongoing and will be presented. Baseline study cohort characteristics. Characteristic HCCN = 25 (34%) BTC N = 12 (16%) EGAN = 12 (16%) CRCN = 11 (15%) PDACN = 8 (11%) Other GI N = 5 (7%) p-value Age Median (25% to 75%) 67 (63 - 76) 68.5 (62.3 – 75.5) 73.5 (62.5 – 75.3) 54 (39.5 – 60) 67.5 (55.5 – 76.3) 60 (57 – 63) 0.008 Baseline TMS Log10 Median (25% - 75%) 3.2 (2.3 – 3.9) 2.5 (2.1 – 3.4) 3.2 (2.2 – 3.8) 4.4 (3.5 – 5) 2.5 (1.9 – 3.3) 4 (3.4 – 5.2) 0.023 Primary tumor present 12 (48%) 8 (66.7%) 12 (100%) 6 (54.5%) 7 (87.5%) 4 (80%) 0.015 First line therapy vs. not 23 (92%) 5 (41.7%) 5 (41.7%) 6 (54.5%) 3 (37.5%) 5 (100%) 0.001 Progressive disease 16 (64%) 4 (33.3%) 9 (75%) 5 (45.5%) 3 (37.5%) 4 (80%) 0.2 Death 13 (52%) 3 (25%) 9 (75%) 7 (63.6%) 3 (37.5%) 2 (40%) 0.2 Kruskal-Wallis rank sum test; Fisher’s exact test.

Challenges in patient selection for surgical options in V600E BRAF–mutated metastatic colorectal cancer.

280 Background: V600E BRAF mutated metastatic colorectal cancer (mCRC), which represents almost 10% of mCRC, is associated with a decreased disease-free interval and increased risk of recurrence compared to other mCRC molecular subtypes; however, data show wide outcome heterogeneity within this subgroup. Surgery is known to be associated with improved outcomes in patients with mCRC, particularly in those with liver-only disease. While many patients with V600E BRAF have very aggressive disease and never have the chance to undergo surgery, it is not clear how to navigate the clinical heterogeneity and choose patients that might benefit the most from loco-regional treatment. Methods: We retrospectively evaluated V600E BRAF mutated mCRC patients from two independent high-volume institutions (MDACC and IOV IRCCS) who underwent metastectomy from Oct 2009 to Oct 2023. Patients with MSI-H disease and those who had R2 surgery were excluded. Clinicopathological features, such as sex, age, histology, radicality and site of surgery, were collected from institutional datasets. Relapse free survival (RFS) was defined as the time from surgery to first relapse or progression. Overall survival (OS) was defined as the time from surgery to the date of death or last follow up. Survival was estimated with the Kaplan Meier method, and the Cox proportional Hazard model was adopted for survival comparison. Results: We collected data from 71 V600E BRAF mutated mCRC patients (N=37 MDACC, N=34 IOV IRCCS); 49% were female, 61% had right-sided primary tumor and 62% had synchronous metastatic disease. Median age at metastatic disease diagnosis was 62 years old (IQR: 61-28). For 52% of patients, surgery was performed on liver-only disease; 35% involved the peritoneum. There were no emergency interventions. Median RFS was 7.9 months (95% CI: 5.4 – 10.5) and median OS was 39 months (95% CI: 28.8 – 51.7). No clinicopathological features, including sex, sidedness, histology, differentiation, presentation (synchronous, oligometastatic), or site of intervention, were associated with RFS. However, radicality (R1) was associated with worse RFS (HR=3.5 [95% CI: 1.8 – 6.5], p=0.0003) and OS (HR=2.7 [95%CI: 1.3 – 5.6], p=0.0122). Conclusions: In this retrospective evaluation of patients with V600E BRAF mutated mCRC who underwent metastectomy, only surgical radicality, observed in the post-operative setting, was associated with recurrence and survival outcomes. Therefore, while surgery should be evaluated whenever radical resection is feasible, the identification of patients with V600E BRAF mutated mCRC who might benefit the most from metastasectomy during pre-operative prognosis evaluation remains challenging.