Citations

e13890 Background: Many oncology practices have reported continued use of telemedicine since onset of the COVID-19 pandemic. However, the future sustainability of telemedicine within oncology practices remains unclear, particularly because federal policies that enabled adoption in response to the public health emergency (PHE) have not been made permanent. Understanding similarities and differences in telemedicine utilization at high-volume oncology centers is crucial for shaping evidence-based policy that enables equitable access to oncology care across varying geographies. Methods: This is a cross-sectional, year-over-year, retrospective cohort analysis of trends in telemedicine utilization across all medical oncology clinical appointments conducted among adult patients (age >18) from January 2019 to December 2023 at Stanford Medicine Cancer Center (SM) – comprising multiple campuses in the California Bay Area – and the Mayo Clinic Comprehensive Cancer Center (MC) – a multiregional cancer practice with tertiary referral campuses in Minnesota, Florida, and Arizona, as well as community-based clinics throughout the Upper Midwest. Results: Both institutions exhibited a similar trend in telemedicine adoption over time. This was characterized by an initial surge in utilization following the PHE declaration in March 2020, followed by sustained utilization rates from 2021 to 2023. However, telemedicine use as a proportion of the overall practice differed significantly between institutions. At SM, the rate of telemedicine visits as a proportion of overall clinical practice was 60.3% (49,136/ 81,502) in 2021, 59.9% (52,247/ 87,215) in 2022, and 57.2% (55,007/ 96,163) in 2023. At MC, the proportion of telemedicine utilization was 12.8% in 2021 (23,873/186,086), 14.7% in 2022 (28,985/196,777), and 14.0% in 2023 (30,208/215,941). Deployment in the setting of new versus return visits also differed between institutions. In 2023, telemedicine accounted for 53.7% (6,440/11,998) of new and 57.7% (48,567/84,165) of return visits at SM, compared to 15.5% (3,359/21,728) and 13.8% (26,849/194,213) at MC. Additionally, while video visits were the predominant modality used to conduct telemedicine visits at both institutions from 2021 onward, in 2023 phone visits still made up 17.9% (5,394/30,208) of all telemedicine visits at MC, compared to just 5.4% (2,990/55,007) at SM. Conclusions: Stanford Medicine and Mayo Clinic exhibited a pattern of initial growth of telemedicine adoption in 2020, followed by sustained utilization from 2021-2023. We observed unique differences in the overall proportion, visit type deployment, and modality of telemedicine utilization between institutions. However, this study confirms telemedicine visits have remained a fixture of medical oncology care for many patients at these institutions since the COVID-19 pandemic.

5048 Background: Ra-223, an alpha-emitting radionuclide, is the first agent of its kind approved for the treatment of mCRPC. Although a pivotal phase 3 study evaluated its short-term safety, there is a need to investigate its long-term safety. The REASSURE study prospectively examined the long-term safety of Ra-223, including secondary primary malignancies (SPMs), in a large patient (pt) population enrolled across Europe, the United States, Israel, and Latin America. Methods: We report final analyses (data cut-off Oct 24, 2024) of REASSURE (NCT02141438), a global, noninterventional study (enrolment 2014–2017). Primary outcomes were the incidence of SPMs, short- (30 days) and long-term (7 years) safety events, and bone marrow suppression (BMS) management in pts who had ≥1 Ra-223 dose. Secondary outcomes included overall survival (OS). Results: Analyses included 1472 pts; median follow-up was 17 months (range 0.3–95.4). Median age was 73 years and 80% of pts had an ECOG PS of 0/1. In evaluable pts, median alkaline phosphatase, prostate-specific antigen, and lactate dehydrogenase levels were 133 U/L, 59 ng/mL, and 266 U/L, respectively. Overall, 81% of pts had bone-only metastases at baseline; 19% of pts had metastases in the bone plus other sites (mostly lymph nodes). Prior treatments included abiraterone (48% of pts), enzalutamide (39%), docetaxel (39%), and cabazitaxel (9%). Pts received a median of 6 Ra-223 doses; 67% received ≥5 doses. SPMs occurred in 2% of pts (25 SPMs in 24 pts). Of these pts, 16 (67%) and 1 (4%) had received prior or concomitant radiotherapy, respectively. Overall, 3% of pts had drug-related serious adverse events >30 days after completing Ra-223. Fractures were reported in 10% of pts and were less common in pts with (7% of 605) than without (12% of 867) concomitant BHA use. During Ra-223 and up to 30 days after the last dose, there was no notable difference in the incidence of abnormal platelet counts between pts with (3%) or without (2%) prior chemotherapy; similar findings were seen for abnormal neutrophil counts (5% and 5%, respectively). BMS treatments, assessed from the start of Ra-223, were more common in pts who had received prior taxanes (38%) than in those who had not (26%). The most common life-prolonging therapies received after Ra-223 were docetaxel (18%), enzalutamide (15%), abiraterone (11%), and cabazitaxel (11%). Median OS was 15.6 months (95% CI, 14.6, 16.4); pt subgroups that survived the longest will be characterized and presented. Conclusions: This real-world safety analysis of pts with mCRPC is the longest follow-up of a radiopharmaceutical reported to date and supports the well-established favorable safety profile of Ra-223. The incidence of SPMs was low. The rate of fracture was low, especially in the presence of BHAs. Prior taxane chemotherapy use had no impact on hematological toxicity. Clinical trial information: NCT02141438 .

e18590 Background: TP53 mutations ( TP53 MUT ) are known to be associated with adverse prognosis in acute myeloid leukemia (AML) and multihit TP53 MUT in myelodysplastic syndromes (MDS). The prognostic relevance of multihit TP53 MUT in myeloproliferative neoplasms (MPN) was recently highlighted. The current study illustrates survival comparisons in multihit TP53- mutated MPN vs. AML and analysis of associated risk factors. Methods: A Mayo Clinic enterprise-wide database search identified 61 MPN and 81 AML cases with multihit TP53 MUT . Conventional statistical methods were used for analyses. Results: 142 patients with multihit TP53 MUT were included: i) chronic phase MPN (MPN-CP; N=19), ii) accelerated phase MPN (MPN-AP; N=14), iii) blast phase MPN (MPN-BP; N=28) and iv) AML, not including MPN-BP (N=81). Concomitant ASXL1 MUT , EZH2 MUT , IDH1 MUT and IDH2 MUT were more common in MPN-BP, compared to AML. At a median follow up of 0.6 years, 124 (87%) deaths and 19 (13%) allogeneic stem cell transplantations (ASCT) were documented. Overall survival (OS), calculated from time of TP53 MUT detection was similar between MPN-BP (median 4.6 months) and MPN-AP (5.6 months; p=0.5). OS in MPN-BP/AP (median 4.8 months) was inferior to that of AML (median 7.4 months; p=0.04) while that of MPN-CP (median 11.6 months) was similar to AML (0.07) but superior to that of MPN-BP/AP (p<0.01). Age-adjusted multivariable analysis (MVA) confirmed the independent prognostic significance of undergoing ASCT (HR 0.4, p=0.03), MPN-CP or achieving response to pre-transplant therapy (HR 0.2, p<0.01), and concurrent TET2 MUT or DNMT3A MUT (HR 2.7, p<0.01) on OS. Based on these risk factors, a 3-tiered risk model was constructed: low (no risk factors; N=18; median OS 23.8 months); intermediate (1 risk factor; N=44; median 11.1 months); and high (2 or more risk factors; N=80; median 4 months; p<0.01). Comparative analysis of risk factors among distinct diseases confirmed the prognostic significance of ASCT (HR 0.3, p=0.03), achieving response to pre-transplant therapy (0.4, p<0.01) and concurrent TET2 MUT or DNMT3A MUT (HR 5.0, p<0.01) in AML. In MPN AP/BP, OS was influenced by having received chemotherapy vs. supportive care (HR 0.1; p<0.01) and achieving response to pre-transplant therapy (0.2, p<0.01). No significant risk factors for OS were identified in MPN-CP. In MVA, ASCT did not appear to influence OS in MPN AP/BP (p=0.7) and MPN-CP (p=0.4) but the number of informative cases was too low to make definitive conclusions. Conclusions: The current study highlights the equally detrimental impact of multihit TP53 MUT in securing long-term survival in MPN and AML. Short-term survival was positively influenced by ASCT, at least in AML, and disease stage or remission status at time of mutation detection and ASCT, respectively.

e15045 Background: Increased cancer cell mitosis in tumor tissue is widely regarded as an indicator of aggressive disease, a predictor of shorter survival, and an indicator of response to specific anthracycline based chemotherapies. Circulating tumor cells (CTCs) are cancer cells that detach from primary tumors, enter the bloodstream, and seed metastatic sites, which in patients (pts) with metastatic breast cancer (mBC) are also predictors of poor prognosis and reduced therapy response. Furthermore, small preliminary studies have identified a specific subtype of mitotic CTCs that appears to correlate with poor survival rates compared to CTC detection alone. However, larger studies have yet to be conducted to validate the clinical utility of mitotic CTCs. In this large multi-institutional prospective study, we isolated CTCs from the blood of n = 155 mBC pts to subtype mitotic CTCs to assess progression-free survival (PFS) and overall survival (OS) over 2 years. Methods: Peripheral blood samples (7.5ml) were prospectively collected from n = 155 mBC pts progressing on systemic therapies and prior to new systemic therapy induction (i.e., chemotherapy n = 90, hormone therapy n = 13, immunotherapy n = 51, targeted therapy n = 62). Samples were processed using CellSieve microfilters to isolate CTCs via size exclusion and fluorescently stained for CD45, Cytokeratin, and DAPI. CTCs were imaged, enumerated, and subtyped based on the presence of ≥1 mitotic event, using established visual indicators. PFS and OS were assessed over 2 years by censored univariate and multivariate analyses. Results: CTCs were detected in ~45% (n = 70/155) of pts, while mitotic CTCs were identified in a subset of this group, ~23% (n = 35/155). The presence of any CTC was associated with poor outcomes (PFS HR = 2.16, 95%CI = 1.4-3.2, p = 0.0002 and OS: HR = 2.51, 95%CI = 1.5-4.0, p = 0.0002). The presence of mitotic CTCs correlated with significantly poorer outcomes (PFS: HR = 5.6, 95%CI = 3.1-10.2, p < 0.0001 and OS: HR = 7.3, 95%CI = 3.7-14.5, p < 0.0001). Overall, pts with no CTCs had a median PFS (mPFS) of 7 months and median OS (mOS) of 24 months, pts with non-mitotic CTCs had a mPFS of 6 months and mOS of 15 months; pts with both CTCs and mitotic CTCs had a mPFS of 3 months and mOS of 5 months. Notably, 97% of pts with a mitotic CTC progressed within 6 months, regardless of systemic therapy type. Interestingly at 2 years, a sole non-progressive pt with a mitotic CTC was receiving alpelisib (a specialized PI3KCA inhibitor). Conclusions: Overall, the detection of CTCs indicated poor outcomes in pts, with mitotic CTCs correlating with significantly more aggressive disease and further reduced survival rates regardless of systemic therapy type. This study highlights the need for larger, more comprehensive studies to expand upon and validate these findings.

e16265 Background: The pivotal TOPAZ-1 trial established durvalumab plus gemcitabine and cisplatin (GC) as a new first-line standard of care for advanced biliary tract cancer (ABTC). However, weekly administration of GC can lead to significant toxicity limiting its tolerability in clinical practice. Based on previous studies, we implemented biweekly regimen of GC on days 1 and 15 together with durvalumab on day 1 of each 28-day cycle to optimize the treatment delivery and improve tolerability. Here, we report the Mayo Clinic experience with biweekly GC with monthly durvalumab in patients with ABTC. Methods: At our three-site institution, we retrospectively identified patients with ABTC between January 2021 and August 2024, who received biweekly GC with monthly durvalumab. Patient demographics, tumor characteristics, treatment details - treatment related adverse events (trAEs) graded according to the NCTCAE V5.0 were collected. Outcomes included median progression-free survival (mPFS), median overall survival (mOS) and clinically assessed overall response rate (ORR) and disease control rate (DCR). Results: 57 patients were included in our analysis, median age was 68 years (range 35-90), and 57.9% were females. 91.2% of patients had ECOG performance status of 0-1. 71.9% had intrahepatic cholangiocarcinoma, 19.3% extrahepatic cholangiocarcinoma and 8.7% gallbladder carcinoma. 70.2% had metastatic disease, 21 % locally advanced unresectable disease and 8.7% recurrent metastatic disease. Patients were followed for a median of 9.1 months (2.3-28.5). 91.2% of the patients received biweekly GC plus monthly durvalumab while 8.8% switched from weekly to biweekly GC plus monthly durvalumab due to treatment toxicities. Median number of treatment cycles was 5. Maintenance regimens included durvalumab (19.3%), gemcitabine/durvalumab (8.8%) and GC/durvalumab (8.8%). Median duration of follow up was 9.1 months (range 2.3 – 28.5). ORR was 36.9% and DCR was 72% (complete response 5.3%, partial response 31.6% and stable disease 35.1%). mPFS was 7.2 months, while mOS was 16 months. Grade(G) 3 or 4 trAEs included abnormal liver function tests (15.7%), infections (11.5%), anemia (8.7%), thrombocytopenia (5.2%), peripheral neuropathy (1.7%), acute kidney injury (1.7%). Immune-related AEs were noted in 6 patients (10.5%) including colitis, gastritis, hepatitis, myocarditis and hypothyroidism. There was no patient with severe neutropenia or febrile neutropenia. Only 5 patients (8.8%) stopped treatment due to trAEs. Conclusions: Biweekly GC on days 1 and 15 plus durvalumab on day 1 of each 28-day cycle is associated with a more favorable toxicity profile while maintaining efficacy similar to that observed in the TOPAZ-1 trial indicating that a de-escalation strategy is feasible with improvement in patient centered outcomes.

5555 Background: Platinum-resistant/refractory ovarian cancer presents a significant therapeutic challenge and despite several attempts, immunotherapies have not delivered satisfactory results to be approved. Identifying biomarkers of response to novel therapies is crucial for personalizing treatments and improving patient outcomes, especially since certain patients do experience long term benefit after the treatment with pembrolizumab and igrelimogene litadenorepvec (TILT-123; an oncolytic adenovirus coding for TNF and IL-2). Methods: Tumor biopsies (n=62), ascites (n=8) and blood (n=234) were collected from 15 patients treated in the PROTA trial (Phase I, NCT05271318). These patients received pembrolizumab intravenously plus igrelimogene litadenorepvec intravenously, followed by local administration intratumorally or intraperitoneally. Sampling took place prior to therapy, during therapy and after it. Tumor proteome (IHC, mIF) and transcriptome was analyzed to assess immune changes and virus presence. Ascites and blood samples were assayed to measure cell counts, phenotypes, cytokine and protein counts, as well as for the presence of antiviral neutralizing antibodies (NAbs). Biological parameters were correlated with overall survival (OS), RECIST 1.1 evaluations and tumor size changes. For analysis of OS, logrank test was used. For group comparisons two-tailed Mann-Whitney U-test was used. Pearson or Spearman tests were used for correlations. Results: Patients experiencing a drop in circulating lymphocytes 8-24 hours after treatment were more likely to experience longer OS (p=0.044). Additionally, patients with a higher lymphocyte count at baseline experienced similar OS benefit (p=0.018) plus a positive correlation with disease control (p=0.023). Most patients (11/15) showed antiviral immunity at baseline but eventually all patients developed neutralizing activity, and the same was observed in ascites. The presence of NAbs at baseline as well as development of highest titers were positively correlated with longer OS (p=0.004) and disease control (p=0.003). Conclusions: Igrelimogene litadenorepvec and pembrolizumab are therapies designed to attract, activate and/or protect lymphocyte-mediated antitumor activity. These findings suggest that having a fit immune system able to mobilize effector immune cells as well as responding to immunostimulant agents increases therapeutic success. As a disease with few therapeutic options, ovarian cancer patients often receive multiple lines of chemotherapy that might decrease the efficacy of immediate immunotherapies. The potential use of these biomarkers will be studied in larger studies to validate their utility in guiding the use of immunotherapy in this challenging patient population. Clinical trial information: NCT05271318 .

e16157 Background: The optimal treatment for resectable gastric/GEJ AC is unclear due to limited direct comparisons among chemotherapy and chemoradiation regimens. Addressing this gap is critical to improve patient outcomes. We performed this network meta-analysis (NMA) to determine the relative efficacy of multimodality regimens for resectable gastric/GEJ AC. Methods: MEDLINE, EMBASE, Scopus, and CENTRAL were searched from inception till September 20, 2024, to identify phase III trials evaluating perioperative/neoadjuvant systemic therapy ± radiation in resectable gastric/GEJ AC. Primary outcomes were disease-free survival (DFS) and overall survival (OS). A frequentist NMA was conducted to compare hazard ratios (HR) and 95% CI for each outcome. Relative treatment rankings were assessed using P-scores. Results: Fifteen trials (8,072 patients) were analyzed. pFLOT (perioperative fluorouracil, leucovorin, oxaliplatin, and docetaxel) ranked highest for DFS in the overall population (P score 91%) (Table), significantly outperforming surgery alone (HR 0.48, 95% CI 0.38-0.60) and nCROSS (neoadjuvant paclitaxel, carboplatin and radiotherapy) (0.67, 0.56-0.81). For OS, nPLF+nCRT(EP) (neoadjuvant cisplatin, leucovorin and fluorouracil for induction, followed by etoposide, cisplatin, and radiotherapy) (P score 90%) and pFLOT (P score 87%) were the top regimens, with pFLOT significantly outperforming surgery alone (0.57, 0.45-0.72), and nCROSS (0.73, 0.60-0.89). Adding neoadjuvant chemoradiation to pFLOT provided no additional OS (1.14, 0.76-1.72) or DFS (1.22, 0.83-1.82) benefit. Similarly, adding pembrolizumab to perioperative chemotherapy (CF/CX) (cisplatin and fluorouracil/capecitabine) was not superior to pFLOT in terms of DFS (1.10, 0.71-1.69) or OS (1.09, 0.69-1.72). Conclusions: pFLOT demonstrated superior efficacy in resectable gastric/GEJ AC, surpassing surgery alone, nCROSS, and other perioperative regimens. The additive role of immunotherapy to pFLOT requires further investigation to refine patient selection and optimize outcomes. Regimen Overall Population GEJ cohort OS DFS OS DFS nPLF+nCRT(EP) 1 (90) 2 (84) 1 (85) NA pFLOT 2 (87) 1 (91) 2 (79) 2 (88) pPembrolizumab+CF/CX 3 (75) 3 (81) 5 (41) - nECX 4 (61) 5 (55) - - pCF 5 (59) 8 (51) 3 (72) - pECF/ECX 6 (47) 6 (55) 7 (40) 3 (57) nECX+aCRT(CX) 7 (45) 7 (52) 9 (31) - nCF 8 (42) 10 (28) 6 (40) - nCROSS 9 (41) 9 (35) 8 (34) 4 (43) pECF/ECX/FLOT+nCRT(F/X) 10 (38) 4 (57) 4 (72) 1 (90) nCRT(CF) 11 (9) 11 (6) - 5 (14) Surgery 12 (7) 12 (5) 10 (5) 6 (9) Data reported as rank (P-score). Abbreviations: n: neoadjuvant; p: perioperative; ECX: epirubicin + cisplatin + capecitabine; CF: cisplatin + fluorouracil; ECF: epirubicin + cisplatin + fluorouracil; aCRT(CX): adjuvant radiotherapy + cisplatin + capecitabine; CRT(F/X): fluorouracil/capecitabine + radiotherapy; CRT(CF): cisplatin + fluorouracil + radiotherapy.

e23317 Background: mCRC poses significant challenges, particularly in patients (pts) who progress after multiple lines of therapy. Limited effective treatment options are available in the advanced chemotherapy-refractory setting. The FRESCO-2 trial demonstrated that Fruq, a selective VEGFR inhibitor, provides meaningful overall survival (OS) benefit in pts with refractory mCRC. However, there is limited real-world evidence regarding Fruq's efficacy in patients treated after approved third-line therapies. Methods: This retrospective, multi-site cohort study evaluated outcomes in 33 mCRC pts who received Fruq following treatment with Rego and/or TAS-102 with or without bevacizumab. Patients were stratified into two groups: Fruq as a second late-line therapy, after either Rego or TAS-102, (27 patients) and as a third late-line therapy, after both Rego and TAS-102, (6 patients). Overall survival (OS) was calculated from Fruq initiation to death, while time to treatment discontinuation (TTD) was defined as the duration from Fruq initiation to cessation for any reason, including death. Survival analysis was performed using the Kaplan-Meier method to estimate median survival, and the comparison between groups were done using the log-rank test. Results: Among the 33 pts, the median age was 58 years (range: 35–84), with 57.6% being male. Hepatic metastases were present in 78.8%, and 60.6% had left-sided primary tumors. RAS mutations were observed in 63.6%, and 97% were BRAF wild-type. Median OS was significantly longer in pts who received Fruq as a second late-line therapy (7.2 months) compared to those receiving it as a third late-line therapy (4.0 months) (p = 0.039). Median TTD was similar between groups (2.4 vs. 2.8 months, p = 0.916). Conclusions: This real-world analysis highlights the clinical benefit of Fruquintinib in mCRC patients following treatment with Regorafenib and/or TAS-102. The data suggest flexibility in treatment choices, with Fruquintinib showing improved OS when used earlier in the treatment sequence. These findings underscore the importance of exploring optimal sequencing strategies and evaluating Fruquintinib as a potential option before other approved agents in the refractory setting. Clinical outcomes with fruquintinib as second vs. third late-line therapy. Fruq as Second Late-Line Fruq as Third Late-Line p-value Median OS 7.2 months 4 months 0.039 Median TTD 2.4 months 2.8 months 0.916 OS: Overall Survival; TTD: Time to Treatment discontinuation.

4166 Background: GN is a front-line therapy for aPDAC. A Phase I/II study demonstrated that GCN has a higher overall response rate and median overall survival (mOS). Our previous study found no difference in outcomes among patients with DNA damage repair gene mutations; however, stromal gene expression correlated with mOS in patients receiving GCN. Here, we further evaluate differences in the outcomes with GCN and GN by site of biopsy. Methods: PDAC samples (n = 4,463) were analyzed by NGS (NextSeq/NovaSeq) or RNA (NovaSeq) (Caris Life Sciences, Phx, AZ). Expression of stromal and related genes ( ACTA2, ADIRF, HAS2, IL-6, MMP-2, MMP-9, SPARC, STAT3, TBGB1, TGFB2, TGFBR3, IDO1, HLA-DRB4, VEGFB) from different biopsy sites [high expression (H) >50% of RNA transcripts per million] was correlated with outcomes to GCN or GN. mOS was obtained from insurance claims and calculated from first treatment to last contact. The hazard ratio (HR) was calculated by the Cox proportional hazards model, and p-values were calculated using the log-rank test. Results: 4325 patients [primary biopsy (PT), n = 1,878; non-liver metastatic biopsy (N-LM), n = 818; Liver biopsy (LM), n = 1,629] received GN while 138 patients (PT, n = 45; N-LM, n = 28; LM, n = 65) received GCN. GCN was associated with longer mOS than GN [∆: 5.2 months (m), HR: 0.76, 95% CI 0.63-0.92, p = 0.01]. GCN was associated with longer mOS compared to GN in LM (∆: 5.6 m, HR: 0.66, 95% CI 0.50-0.87, p = 0.003), but it was not significant in PT (∆: 4.6 m, p = 0.13) and N-LM (∆: 4.4 m, p = 0.35). Median MMP2 (38.5 vs. 163.1 vs. 162.2), VEGFB (14.4 vs. 16.9 vs. 16.2) and TGFBR3 (11.4 vs. 15 vs. 16.4) expression were lower in LM compared to PT and N-LM while TGFB1 (41.6 vs. 34.5 vs. 39.8) and IL6 (1.61 vs. 1.19 vs. 1.41) expression were highest in LM (p < 0.05). In LM, IL6 -H (∆: -11 m, p = 0.037) and TGFB1 -H (∆: -5.9 m, p = 0.10) were associated with worse post-GCN survival compared to GN (p = 0.82 and p = 0.57). Whereas, in N-LM, TGFBR3 -H trended towards longer post-GCN survival (∆: 12 m, p = 0.18), while ADIRF -H trended towards shorter post-GCN survival (∆: -12 m, p = 0.056) compared to GN (p = 0.42 and p = 0.10). While in PT, MMP2 -H (∆: 11.3m, HR: 0.46, p = 0.16), TGFB1 -H (∆: 11.3 m, HR: 0.33, p = 0.09), HLA-DRB4 -H (∆: 12.9 m, HR: 0.44, p = 0.11) and VEGFB -H (∆: 10.7, HR: 0.34, p = 0.09) trended towards longer post-GCN survival compared to GN ( MMP2 -H, ∆: 3.4 m, p = 0.03, TGFB1 -H, p = 0.661, HLA-DRB4 -H, p = 0.67, VEGFB-H , ∆: 1.3 m, p = 0.03). Conclusions: GCN is associated with improved mOS compared to GN, especially in LM.Stromal gene expression in the liver differs from that in N-LM and the pancreas. While high stromal gene expression trends towards worse post-GCN survival in LM, it is associated with improved survival in N-LM and PT. Further validation is needed to understand the impact of stromal gene expression in different tumor sites on survival outcomes and signature development.

e16457 Background: Patients with inoperable stage II-III pancreatic cancer commonly undergo sequential stereotactic body radiation therapy (SBRT) and chemotherapy. However, there is variability in clinical outcomes, and the predictors of high-risk patients with rapid tumor progression (within 3 months) and poor overall survival (OS) despite treatment are not well characterized. We developed a radiomic (imaging-derived features) signature (RS) that predicts rapid progression. We then investigated clinical characteristics, including pathologic features and treatments received, and RS in a combined analysis to develop and validate the highest-performing model to predict OS from the time of SBRT initiation. We identified the most predictive feature from the combined model that best predicts OS. Methods: In our retrospective study, we examined a cohort of 124 stage II-III pancreatic cancer patients who underwent sequential SBRT and systemic chemotherapy and had pre-treatment pancreatic protocol computed tomography (CT) imaging. We examined 10 clinical features and extracted 900 radiomic features from each segmented tumor per patient using PyRadiomics. Dividing our cohort into training and test sets (60:40), we built a prediction model for rapid tumor progression using radiomic data on the training set (n = 74), applying a LASSO-based algorithm for feature selection and 5-fold cross-validation for parameter optimization. We validated the model performance on the held-out test set (n = 50) and generated the RS for predicting rapid progression. We examined the performance of clinical features and RS in predicting OS in univariate and multivariate Cox regression models. Results: Analysis on our cohort (57 men, 67 women; mean age 67 ± 11 years) generated a 43-feature RS that predicted rapid tumor progression (AUC 0.83, 95% CI: 0.70–0.94) in the test set. High RS was a significant predictor of mortality with hazard ratio (HR) 2.22 (95% CI: 1.32–3.73, p = 0.003) within the first year and 2.85 (95% CI: 1.35–6.03, p = 0.006) thereafter. Non-intensive chemotherapy increased only early mortality risk (HR 1.95, 95% CI: 1.08–3.53, p = 0.03), while older age was significant in later years (HR 1.80, 95% CI: 1.02–3.15, p = 0.04). Conclusions: CT-derived RS accurately predicted rapid tumor progression in stage II-III pancreatic cancer patients undergoing SBRT sequentially with chemotherapy. High RS was the strongest prognostic indicator for increased mortality risk, suggesting its utility for guiding treatment or selection for clinical trials.