Battaglin, Francesca

Abstract Endocytosis regulates receptor trafficking and signaling, yet its role in colorectal cancer (CRC) remains unclear. We analyzed transcriptomic data from 15,025 CRC tumors to evaluate gene expression in clathrin-mediated endocytosis (CME) and the endosomal sorting complexes required for transport (ESCRT) pathway. Pathway-level signatures were compared across consensus molecular subtypes (CMS) and examined in relation to oncogenic signaling programs, while individual endocytosis-related genes were evaluated for associations with clinical outcomes in an independent randomized trial cohort. Expression of CME and ESCRT pathways varied by CMS, with the highest expression in CMS4 and the lowest in CMS3. Endocytosis signatures correlated with multiple oncogenic signaling pathways, including MAPK, TGF-β, WNT, PI3K, NOTCH, and angiogenesis, suggesting broad links between endocytic activity and tumor biology. In the randomized phase III CALGB/SWOG 80405 trial, low expression of AP2M1 —a core adaptor in the CME complex—was significantly associated with longer overall survival and progression-free survival in patients treated with anti-EGFR agents, but not in those receiving anti-VEGF agents. These findings suggest that endocytic trafficking may be associated with oncogenic signaling and differential therapeutic benefit in patients with metastatic CRC. The endocytosis pathway reflects biologically relevant heterogeneity in CRC and may help guide therapeutic stratification.

198 Background: The Hedgehog (Hh) signaling pathway regulates tissue patterning, growth and differentiation, including within gastrointestinal tract. Mammalian homologs include Sonic (SHH), Indian (IHH) and Desert (DHH) Hedgehog, which signal through PTCH and SMO and the GLI transcription factors. In the digestive tract, both SHH and IHH are expressed, but the functional role of Hh signaling in mCRC remains incompletely defined. Methods: We analyzed 433 mCRC patients treated with either bevacizumab (bev = 226) or cetuximab (cet = 207) plus first line chemotherapy in CALGB/SWOG 80405 (NCT00265850). RNA expression (Illumina HiSeq 2500) of 9 Hh pathway genes (SHH, IHH, DHH, PTCH1, PTCH2, SMO, GLI1, GLI2, GLI3) was evaluated. Median overall survival (mOS) and progression free survival (mPFS) in months (mo) were compared across expression tertiles (low [L], medium [M], high [H]). Likelihood ratio tests, hazard ratios and 95% confidence intervals were computed from multivariable Cox proportional hazards models, adjusting for age, sex, ethnicity, ECOG PS, tumor location, number of metastatic sites, KRAS , microsatellites instability status and treatment. Prognostic effects were modeled as marginal terms; predictive effects were modeled as multiplicative interactions. Results: Overall, IHH and GLI2 demonstrated prognostic value for OS after adjusting for multiple testing (Benjamini-Hochberg False Discovery Rate (FDR) < 0.05). High IHH expression (H group, n = 143) correlated with improved mOS (H: 36.0 mo vs M: 32.8 mo vs L: 23.5 mo; p= 0.031), whereas low GLI2 expression (L group, n = 145) was associated with longer mOS (H: 25.6 mo vs M: 33.9 mo vs L: 33.7 mo; p= 0.0016). Moreover, IHH showed predictive value for cet benefit in both OS (mOS H: 38.1 mo vs M: 34.0 mo vs L: 18.4 mo; p= 0.0032) and PFS (mPFS H: 12.6 mo vs M: 12.9 mo vs L: 8.8 mo; p= 0.0025) with significant treatment interaction for OS and PFS (p= 0.0046 and p= 0.0049, respectively; FDR< 0.05). No significant associations were found in bev treated pts. No other Hh genes showed significant prognostic or predictive effects after FDR correction. Conclusions: These results highlight a dual role of Hh pathway in mCRC. Consistent with prior preclinical evidence, reduced IHH expression appears to mark poor prognosis, likely reflecting the loss of IHH-mediated restraint on Wnt signaling, which drives proliferation and dedifferentiation. Conversely, low GLI2, a downstream transcription factor, was linked with favorable outcomes, underscoring context-specific effects of Hh signaling. The strong predictive association of IHH with cet efficacy supports its potential as a biomarker in RAS wild type mCRC. These results suggest that Hh pathway modulation, particularly IHH signaling, may influence disease biology and treatment response. Validation in independent cohorts and mechanistic studies is warranted to clarify implications.

179 Background: Neuroligins are a family of postsynaptic cell adhesion molecules that play a crucial role in synapse formation and function. Recent studies suggest Neuroligin family genes (NLGN1,2,3,4X) may promote cancer cell growth and metastasis in various cancers, including colorectal cancer. Here, we investigated the association between neuroligin family gene expression and first-line treatment outcomes in mCRC. Methods: We evaluated the expression of 4 genes in the neuroligin family (NLGN1, NLGN2, NLGN3 and NLGN4X) on treatment outcomes of 433 pts with mCRC treated with either bevacizumab (Bev, n = 226) or cetuximab (Cet, n = 207) in combination with first-line chemotherapy within the CALGB/SWOG 80405 trial. mRNA was isolated from FFPE tumor samples and sequenced on the HiSeq 2500 (Illumina). Overall survival (OS) and progression-free survival (PFS) were compared between groups of pts categorized by low expression (Q1) (≤25 percentile), medium expression (Q2-3) (25th-75th percentile) and high expression (Q4)(>75th percentile) of NLGN family genes. The associations between gene expression and clinical outcomes were assessed via the multivariable Cox model and plotted with Kaplan-Meier curve. Treatment-gene interactions were evaluated using the likelihood ratio test. False discovery rate (FDR) was controlled through the Benjamini-Hochberg procedure. Results: High NLGN2 expression was associated with shorter PFS (median 10.0 mos, 95% CI (8.3, 11.3)) and OS (median 25.2mos, 95%CI (20.9, 30.0)) compared to low NLGN2 expression (PFS: median 11.2mos, 95% CI (9.8,14.3))(HR 1.41, 95% CI (1.06, 1.89)), P = 0.029). (OS: (median 31.8mos, 95%CI (26.8, 37.5)( HR 1.49, 95% CI (1.10, 2.01) P =0.0095) in multivariate analysis. Patients treated in the cetuximab arm(n=207), high HLGN2 expression significantly associated with shorter PFS (median 8.0 vs 13.4, HR 2.02, 95% CI (1.35, 3.03), P = 0.0021) and OS (median19.6 vs 36.3, HR 2.30, 95% CI (1.50, 3.53), P =8.3e-05). High NLGN3 expression was associated with shorter OS (23.9 vs 36.0 mos, P =0.0083) in cetuximab treatment arms, no significance found in PFS. We found significant treatment interaction for OS with NLGN2 and NLGN3 favoring cetuximab. In pts treated with cetuximab, High NLGN2 expression was significantly associated with shorter OS (median 29.1vs 36.3) (p=0.024) compared to pts treated with bevacizumab. For NLGN3, pts treated with cetuximab, high NLGN3 expression was significantly associated with shorter OS (median 25.0 vs 36.0) (p=0.018) compared to pts treated with bevacizumab. No significant association was found in NLGN1 and NLGN4X. Conclusions: Our results suggest NLGN2/3 gene expression may predict mCRC treatment outcomes. Potential therapeutic drug target NLGN in combination with anti-EGFR treatment in mCRC is warranted.

3145 Background: SnoRNAs are non-coding RNAs that primarily guide the chemical modification of ribosomal RNA. Emerging evidence suggests snoRNAs play critical roles in cancer, including CRC, by regulating cell proliferation, apoptosis and tumor progression. Aberrant snoRNA expression has been linked to CRC development and poor prognosis, offering potential as diagnostic biomarkers and therapeutic targets. We investigated whether the tumor expression levels of 3 types of snoRNAs (SCARNA, SNORA, SNORD) affect treatment response in pts enrolled in CALGB/SWOG 80405 (NCT00265850). Methods: 433 mCRC pts treated with bevacizumab (bev, n = 226) or cetuximab (cet, n = 207) in combination with first-line chemotherapy were analyzed. RNA was isolated from FFPE tumor samples and sequenced on the HiSeq 2500 (Illumina). 422 snoRNAs were evaluated (23 SCARNA, 140 SNORA, 259 SNORD). Overall survival (OS) and progression-free survival (PFS) were compared across tertiles of gene expression (high [H], medium [M], low [L]) by multivariable Cox proportional hazards models adjusted for age, sex, ECOG performance status, tumor side, number of metastatic sites, KRAS , CMS subtypes, and treatment. Interaction tests for the predictive effect (bev vs cet) were performed. P -values were corrected for multiple testing using the Benjamini-Hochberg approach ( q < 0.05). Results: Only SCARNA21 achieved statistical significance for OS after false discovery rate (FDR) adjustment. Tumors with H levels of SCARNA21 had shorter survival compared to tumors with M or L expression (median OS 24.4 vs 32.4 vs 33.9 months, respectively; P = 0.0015, q = 0.033), independent of treatment. No snoRNAs achieved FDR significance for PFS. However, several snoRNAs showed significant treatment interactions with biologic agents. SCARNA6-H and SCARNA5-H tumors had longer PFS and OS when treated with cet, but shorter PFS and OS when treated with bev, compared to the M and L expression groups (PFS interaction q = 0.0067 and 0.045, respectively; OS interaction q = 0.022 and 0.034, respectively). SCARNA7 also showed significant treatment interaction for OS, favoring cet in the H expression group ( q = 0.018); the opposite was observed for SNORA63B, SNORA63D, SNORA35B, and SNORA36C ( q = 0.027, 0.027, 0.027 and 0.047, respectively). No significant results were observed for any of the tested SNORDs. Conclusions: SnoRNAs dysregulation affects key pathways such as cell cycle control and immune evasion, making them promising players in CRC biology. Our study highlights the prognostic and predictive potential of specific snoRNAs in mCRC. Notably, high SCARNA21 expression was linked to shorter OS, while SCARNA5 and 6 showed predictive value for treatment response, indicating their potential for guiding treatment decisions. Further validation is needed to confirm these findings, and mechanistic studies are warranted.

3128 Background: LncRNAs have emerged as key regulators of cancer progression and therapeutic responses. In CRC, several lncRNAs have been implicated in modulating tumor growth, metastasis and treatment resistance by interacting with critical tumorigenic pathways. Here, we investigate the potential prognostic and predictive value of lncRNA expression in patients (pts) with mCRC enrolled in CALGB/SWOG 80405 (NCT00265850) trial. Methods: We analyzed 433 mCRC pts treated with either bevacizumab (bev, n = 226) or cetuximab (cet, n = 207) plus first-line chemotherapy. Tumor RNA expression (Illumina HiSeq 2500) of 13 candidate lncRNAs (SNHG11, HOTAIR, FGF14-AS2, H19, YWHAE, NEAT1, MIR100HG, UCA1, LINC00973, SLCO4A1-AS1, POU5F1P4, MALAT1, HCG18) was explored. Median overall survival (mOS) and progression-free survival (mPFS) in months (mo) were compared between pts grouped by tertiles (low [L] vs medium [M] vs high [H]) of gene expression. Likelihood ratio tests, hazard ratios and 95% confidence intervals were computed from multivariable Cox proportional hazards models, adjusting for age, sex, ECOG PS, tumor location, number of metastatic sites, KRAS , Consensus Molecular Subtypes (CMS), and treatment. Results: Overall, SNHG11 was strongly associated with OS and PFS after adjusting for multiple tests (Benjamini-Hochberg False Discovery Rate < 0.05). High SNHG11 expression (H group, n = 144) was associated with improved mPFS (H: 14.3 vs M: 11.2 vs L: 8.3 mo; p = 0.038) and mOS (H: 39.6 vs M: 31.1 vs L: 20.5 mo; p = 0.033) in the combined treatment analysis. Among cet-treated pts, SNHG11-H showed a numerically longer mPFS (H: 14.2 vs M: 11.1 vs L: 7.6 mo; p = 0.19) and significantly longer mOS (H: 41.1 vs M: 32.4 vs L: 14.3 mo; p = 0.012). In contrast, no statistically significant OS or PFS differences were observed in bev-treated pts. SNHG11-H tumors had a significant OS benefit from cet compared to bev (mOS 41.1 vs 36.5 mo, respectively; p = 0.016), with a nominally significant treatment interaction observed for OS (p = 0.030). No significant differences were observed in the L or M expression groups. Additional analyses showed that SNHG11 expression was high in the CMS2 (canonical) subtype and substantially lower in CMS1 (immune). Conclusions: LncRNA SNHG11 plays a significant role in CRC progression and metastasis via tumorigenic pathways, including c-Myc and HIF-1α. Moreover, elevated circulating SNHG11 levels show promise as a non-invasive biomarker for early CRC detection. In CALGB/SWOG 80405, high SNHG11 expression correlated with improved PFS and OS, particularly in cet-treated pts, supporting its role as a prognostic and predictive biomarker. Its strong association with CMS2 aligns with its reported involvement in c-Myc-driven pathways. Further validation is needed to confirm the clinical utility of this biomarker and elucidate underlying mechanisms.

Background. MicroRNAs are small, single-stranded non-coding RNA molecules that play major role in gene regulation. miRNAs have been reported as both tumor suppressive and oncogenic and are promising candidates for cancer prognosis and treatment. miR-494 is known to promote cell migration and invasion in CRC. Our study aimed to further explore the role of miR-494 modulation (inhibition and overexpression) in CRC. Methods. We evaluated the impact of tumor gene expression of MIR494 on outcomes (overall survival: OS; progression-free survival: PFS) in data for 433 metastatic CRC (mCRC) patients (pts) (bevacizumab [bev] (N = 226) vs cetuximab [cet] (N = 207)) enrolled in randomized phase III CALGB/SWOG 80405 trial obtained from Alliance for Clinical Trials in Oncology. RNA extracted from FFPE tumor samples was sequenced using the HiSeq 2500 (Illumina). Gene expression was divided into high, medium and low. Associations were assessed by log-rank test and multivariable Cox proportional hazards regression model. Treatment-gene interactions were analyzed using the likelihood ratio test. CRC cell lines HCT116 and HT29 were transfected with miR-494 inhibitors and mimics for 48 hours and total RNA was collected, followed by RT-qPCR (miR-494 and target genes BMAL1, PAK1, CDH1, CDH2, SNAI1, TWIST) and clonogenic assays. Results. High miR-494 was significantly associated with worse PFS in overall (median survival: high vs low: 9.3 vs 11.3 months, P&lt;0.025) and cet-treated (median survival high vs low: 9.2 vs 9.6 months, P&lt;0.025) mCRC cohorts, while no significance was observed in bev-treated mCRC. Multivariable Cox model showed significant association between high miR-494 and worse PFS and OS in the cet-treated cohort; however, treatment-gene interaction was not statistically significant. Expression analysis revealed miR-494 was significantly reduced and increased following inhibitor and mimic transfection, respectively. Differential gene expression of the target genes analyzed was observed between the miR-494 inhibitor and mimic-treated HCT116 and HT29 samples. In HCT116 cells, inhibition of miR-494 significantly (P &lt; 0.01) reduced expression of PAK1, while increased the expression of CDH1. The number of colonies formed relatively increased after transfection with miR-494 inhibitor compared to miR-494 mimic. Conclusion. Our findings showed that high miR-494 expression correlated with worse PFS overall and in cet-treated mCRC pts. It would be interesting to check for potential associations with EGFR signaling (direct or indirect). Further studies are warranted for efficient targeting and to gain better understanding of the associated signaling involved in miR-494 modulation in CRC. Support: U10CA180821, U10CA180882; U10CA180888 (SWOG): Genentech. https://acknowledgments.alliancefound.org; P30CA014089, UG1CA180830 [HJL]. Clinicaltrials.gov Identifier: NCT00265850 Citation Format: Pooja Mittal, Joshua Millstein, Shivani Soni, Francesca Battaglin, Karam Ashouri, Sandra Algaze, Priya Jayachandran, Yan Yang, Lesly T. Gonzalez, Unnati H. Shah, Wu Zhang, Fang-Shu Ou, Alan P. Venook, Indrakant K. Singh, Heinz J. Lenz. Effect of miR-494 modulation in colorectal cancer (CRC): Clinical outcome, target expression and cell characteristics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2787.

224 Background: Metabolic pathways are reprogrammed during CRC development, leading to increased glycolysis, glutaminolysis, and fatty acid synthesis. Understanding the impact of metabolic reprogramming on treatment outcomes is paramount. Hence, we investigated whether the tumor gene expression of 4 selected major metabolic genes ( PKM, SLC2A1 , SLC16A1 , and CAV1 ) could affect treatment response in pts enrolled in the CALGB/SWOG 80405 trial. Methods: 433 mCRC pts treated with either bevacizumab (bev, n = 226) or cetuximab (cet, n = 207) in combination with first-line chemotherapy were analyzed. RNA was isolated from FFPE tumor samples and sequenced on the HiSeq 2500 (Illumina). Overall survival (OS) and progression-free survival (PFS) were compared between groups of pts categorized by tertiles of gene expression (high [H], medium [M] and low [L]). Logrank P -values provide a non-parametric unadjusted assessment of differences. Likelihood ratio tests (LRT) were computed from multivariate Cox proportional hazards models, adjusting for age, sex, ECOG, tumor side, number of metastatic sites, KRAS , CMS, and treatment. Results: PKM gene expression was associated with cet treatment outcomes with PKM- low tumors showing significantly longer PFS and OS (median PFS: 14.3 vs 9.8 vs 8.1 months, L vs M vs H, P < 0.0001, LRT P = 0.011; median OS: 45.9 vs 31.2 vs 20.9 months, P < 0.0001, LRT P = 0.12). Low SLC2A1 was also associated with longer OS in cet-treated pts (32.4 vs 35.8 vs 25.2 months, P = 0.02, LRT P < 0.0001). Similar results were observed in bev-treated pts where low SLC2A1 expressing tumors had longer OS (37.4 vs 26.1 vs 29 months, P = 0.037, LRT P = 0.069) and a non-significant trend for longer PFS (13.1 vs 11 vs 9.5 months, P = 0.076). CAV1 low gene expression was associated with longer OS in cet-treated pts (37.4 vs 34 vs 21.5 months, P = 0.0048, LRT P = 0.013), while no significant associations were found in bev-treated (interaction LRT P = 0.0009). No significant results were observed for SLC16A1 . Conclusions: The intratumoral expression of metabolic genes was prognostic and predictive in mCRC pts treated with first-line therapy. GLUT1 (encoded by SLC2A1 ) and PKM2 (encoded by PKM ) promote aerobic glycolysis of cancer cells, known as Warburg effect, supporting rapid cell proliferation and survival. CAV1 has been shown to be involved in mitochondrial bioenergetics and fatty acid metabolism and to play either a tumor suppressor or oncogenic role depending on the cancer type and stage. Lower expression of SLC2A1 and PKM was associated with improved survival and increased benefit from cet treatment in our cohort. Low CAV1 expression was also associated with increase survival suggesting a cancer-promoting role in mCRC. Our results suggest that targeting cancer cell metabolism through novel inhibitors of the aforementioned pathways may be a promising therapeutic strategy.

269 Background: Sirtuins (SIRT1-7) are class III histone deacetylases with different roles in CRC as tumor suppressive and oncogenic, mainly influencing proliferation, migration, invasion, DNA damage and chemoresistance. In the present study, we explored the association between tumor gene expression of sirtuins and first-line treatment outcomes in mCRC pts. Methods: We evaluated the impact of the tumor gene expression of sirtuin genes ( SIRT1 -7) on treatment outcomes (overall survival: OS; progression free survival: PFS) in 433 pts enrolled in the randomized, phase III CALGB/SWOG 80405 (NCT00265850) trial. RNA extracted from FFPE tumor samples was sequenced using the HiSeq 2500 (Illumina). Subgroup analyses were based on treatment (bevacizumab [bev] (N = 226) vs. cetuximab [cet] (N = 207)). For each gene, expression was divided into tertiles of high, medium and low. The associations between tumor gene expression and outcomes (PFS and OS) were assessed using log-rank test in univariate analysis. Multivariable Cox proportional hazards regression model was used to compute hazard ratios (HR) and 95% confidence intervals while adjusting for baseline characteristics. Treatment-gene interactions were analyzed using the likelihood ratio test. Results: Of the seven genes analyzed, SIRT3 high was associated with both longer PFS (HR: 0.59 [95% CI: 0.46-0.74], P < 0.001) and OS (HR:0.64 [95% CI: 0.50-0.83], P = 0.002) overall. Treatment-gene interaction testing found significant interactions for SIRT1 and SIRT5 with PFS ( P values: 0.021 and 0.016, respectively) and OS ( P values: 0.038 and 0.014, respectively) with targeted therapies (bev vs. cet). Multivariate analysis showed SIRT1 high associated with longer PFS (HR: 0.62 [95% CI: 0.42-0.89], P = 0.014) and OS (HR: 0.59 [95% CI: 0.40-0.89], P = 0.036) in cet-treated pts; in contrast with shorter observed PFS (HR: 1.38 [95% CI: 0.96-1.99], P = 0.22) and OS (HR: 1.31 [95% CI: 0.90-1.93], P = 0.23) in bev-treated pts. SIRT5 high showed similar results and associated with longer PFS (HR: 0.64 [95% CI: 0.45-0.91], P = 0.039) and OS (HR: 0.57 [95% CI: 0.39-0.83], P = 0.013) in cet-treated pts, with no similar associations in bev-treated pts. Conclusions: Our results highlight a potential role for SIRT3 as prognostic and, SIRT1 and SIRT5 as predictive biomarkers for first-line treatment in mCRC, with differential effects based on targeted agents. Significant interaction favored cet treatment in SIRT1 high and SIRT5 high tumors. However, previous reports suggest an opposite role of SIRT5 that has been linked to chemotherapy and/or cet resistance in CRC via the inactivation of succinate dehydrogenase complex subunit A. Therefore, further studies are warranted to dissect the mechanism behind the interaction of SIRT5 with cetuximab activity and establish the potential of targeting SIRT1/5 in CRC.

254 Background: SLFN11 was recently identified as a dominant determinant of response to DNA-damaging anticancer agents. Several studies showed SLFN11 expression led to better sensitivity to topoisomerase inhibitors and PARP inhibitors. However, clinical evidence in mCRC has been lacking. Methods: Two independent cohorts (CALGB/SWOG 80405 trial and a real-world patient [Caris CODEai] cohort) were included in this study. Patients were stratified into SLFN11 -high and -low groups based on the median SLFN11 gene expression levels. Survival outcomes were compared between SLFN11 -high and SLFN11 -low in irinotecan-treated and oxaliplatin-treated patients. Median time was estimated using Kaplan-Meier method and Cox models were used for covariate adjustment. Endpoints of interest were progression-free survival (PFS) and overall survival (OS). Results: In the CALGB/SWOG 80405 trial cohort, 433 patients were included (110 treated with FOLFIRI-based chemotherapy and 323 treated with FOLFOX-based chemotherapy). In patients treated with FOLFIRI-based chemotherapy, SLFN11 -low patients exhibited numerically better PFS (median PFS, 13.4 vs 11.2 months, log-rank p = 0.03, adjusted hazard ratio [HR] = 0.86, 95% confidence interval [CI] 0.55-1.39, p = 0.50) and OS (median OS, 39.6 vs 30.3 months, log-rank p = 0.02, adjusted HR = 0.73, 95% CI 0.46-1.16, p = 0.19) compared to SLFN11 -high patients. In patients treated with FOLFOX-based chemotherapy, SLFN11 -low patients exhibited numerically better PFS (median PFS 11.2 vs 9.8 months, log-rank p = 0.03, adjusted HR = 0.83, 95% CI 0.65-1.05, p = 0.12) and OS (31.1 vs 26.1 months, log-rank p = 0.07, adjusted HR = 0.84, 95% CI 0.65-1.08, p = 0.16) compared to SLFN11 -high patients. No significant interaction was observed between treatment and SLFN11 expression in terms of PFS ( p = 0.69) and OS ( p = 0.44). In the Caris CODEai cohort, a better OS in SLFN11 -low patients than in SLFN11 -high patients was observed in irinotecan-treated patients ( N = 2906) (median OS, 25.5 vs 21.7 months, HR = 0.90, 95% CI 0.82-1.00, p = 0.048). However, no significant difference in OS between SLFN11 -low and SLFN11-high was observed in oxaliplatin-treated patients ( N = 4428) (median OS, 39.5 vs 35.8 months, HR = 0.98, 95% CI 0.90-1.06, p = 0.56). Conclusions: Low SLFN11 expression showed a potential for better prognosis in mCRC patients receiving irinotecan- and oxaliplatin-containing chemotherapies. These findings are not consistently aligned with preclinical data and clinical evidence in other cancer types previously reported. Further investigation is warranted to better understand the biological role and clinical implication of SLFN11 in mCRC.

285 Background: Immune checkpoint inhibitors (ICIs) have shown limited efficacy in colorectal cancer (CRC) outside of mismatch repair (MMR) deficient/microsatellite instability-high (MSI-H) tumors. Most CRC cases are MMR proficient /microsatellite stable and demonstrate resistance to ICIs, attributed to the tumor microenvironment. Colony Stimulating Factor 1 Receptor (CSF1R), a regulator of tumor-associated macrophages, has emerged as a potential target due to its association with poor prognosis in CRC. Methods: Data from 433 metastatic CRC (mCRC) patients in the CALGB/SWOG 80405 trial were analyzed. CSF1R RNA was extracted from formalin-fixed, paraffin-embedded tumor samples and sequenced. Patients were divided into tertiles of CSF1R expression (high, medium, low). Progression-free survival (PFS) and overall survival (OS) were compared using Kaplan-Meier curves, log-rank tests, and Cox proportional hazards models. Subgroup analyses were conducted based on liver metastases, treatment type (Bevacizumab, Cetuximab, FOLFOX, FOLFIRI), and MSI status. Results: Low CSF1R expression (CSF1R-L) was associated with significantly better survival outcomes. Median PFS was 12.9 months for CSF1R-L, compared to 11.2 and 9.2 months for CSF1R-M and CSF1R-H (p = 0.003). Median OS was 35.8 months for CSF1R-L versus 32.5 and 24.4 months for CSF1R-M and CSF1R-H (p = 0.00086). Stratification by liver metastases showed that CSF1R-L remained a strong prognostic factor only in patients with liver metastases. There were no significant survival differences based on CSF1R expression in bevacizumab-treated patients. However, in cetuximab-treated patients, CSF1R-L tumors had significantly longer PFS (12.9 vs 8.8 months, p = 0.037) and OS (35.8 vs 21.4 months, p = 0.002) than CSF1R-H tumors. Similarly, in FOLFOX-treated patients, CSF1R-L tumors showed longer PFS and OS (p = 0.018 and p = 0.013, respectively), and in FOLFIRI-treated patients, OS was significantly longer for CSF1R-L tumors (42.2 vs 24.7 months, p = 0.022) than CSF1R-H tumors. Conclusions: Our data suggests that CSF1R expression may serve as a prognostic biomarker in CRC, with lower expression potentially linked to improved survival, particularly in patients with liver metastases. These findings warrant further investigation of CSF1R as a possible prognostic and predictive biomarker, as well as a potential therapeutic target in CRC. Clinical trial information: NCT00265850 .