Torres‐Gonzalez, Lesly

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 .

3588 Background: The brain-gut axis, a bidirectional network between the central and enteric nervous systems, plays a critical role in modulating the gastrointestinal tract function. Increasing evidence suggests that neuronal signaling molecules can promote gastrointestinal cancers; however, the mechanisms remain unclear. Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter and dysregulated GABA signaling has been found in CRC, affecting both tumor and tumor microenvironment. Here, we investigated the association between tumor GABA pathway gene expression and first-line treatment outcomes in mCRC. Methods: We evaluated the impact of the expression of 25 genes in the GABA pathway ( GABBR1, GABBR2, GABRA1, GABRA2, GABRA4, GABRA5, GABRA6, GABRB1, GABRB3, GABRD, GABRE, GABRG1, GABRG2, GABRG3, GABRQ, GABRR1, GABRR2, ABAT, ALDH5A1, GAD1, GAD2, SLC6A1, SLC6A13, SLC6A11, SLC6A12) on treatment outcomes (overall survival: OS; progression free survival: PFS) of 433 pts enrolled in the randomized, phase III CALGB/SWOG 80405 trial. RNA extracted from FFPE tumor samples was sequenced using the HiSeq 2500 (Illumina). The associations between gene expression (continuous, per standard deviation increase) and outcomes were assessed via the multivariable Cox proportional framework, with hazard ratios (HR) and 95% confidence intervals (CI) computed. The likelihood ratio test was used for interaction tests. False discovery rate (FDR) was controlled at 5% with the Benjamini-Hochberg method. Results: Overall, low GAD1 (encoding for glutamate decarboxylase 1, the enzyme responsible for catalyzing the production of GABA from L-glutamic acid) was associated with longer PFS (HR: 1.26, 95% CI [1.13, 1.41], P = 3.2E-05) and OS (HR 1.27 [1.13, 1.43], P = 5.9E-05) across all treatment arms. High ABAT (encoding for the aminotransferase responsible for GABA catabolism) was also associated with longer OS (HR 0.81 [0.72, 0.91], P = 6E-04). To evaluate the predictive value, interactions with targeted therapies bevacizumab (n = 226) vs cetuximab (n = 207) were tested. We found significant interactions for PFS with ABAT ( P= 0.0017) and OS with SLC6A13 ( P= 0.0014 ).In pts treated with cetuximab, high ABAT expression was significantly associated with longer PFS (HR 0.73 [0.61, 0.87], P = 2.8E-04), and high SLC6A13 was marginally associated with worse OS (HR 1.18 [1.00, 1.39], P = 0.052). We did not observe similar associations in pts treated with bevacizumab. Conclusions: Our results highlight a potential role for GABA signaling in affecting mCRC treatment outcomes, suggesting that GABA pathway genes may be promising novel predictive and prognostic biomarkers and supporting the rationale to investigate GABA as a target for drug development. ClinicalTrials.gov Identifier: NCT00265850

3144 Background: Longitudinal brain structure changes across the lifespan are associated with neurodegenerative disorders. We previously showed that genetic variants in dopamine and Parkinson’s disease genes are predictive and prognostic in mCRC. Indeed, the brain-gut axis is emerging as a critical player in CRC biology. Hence, we investigated whether the tumor gene expression of 3 metabolic genes involved in brain development and aging could affect treatment response in patients 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 included in the analysis. 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 expression of 3 genes: APOE, DACH1, and GPR139. Likelihood ratio tests, hazard ratios and 95% confidence intervals were computed from multivariate Cox proportional hazards models, adjusting for age, sex, ethnicity, ECOG PS, tumor location, number of metastatic sites, KRAS, MSI status, and treatment. Logrank P-values describe differences without adjustment for patient characteristics. Results: Both APOE and DACH1 (but not GPR139) met the 0.05 false discovery rate threshold for association with both PFS ( P = .00085, P = .015) and OS ( P = .021, P = .021, respectively) in the full Cox models. In cet-treated pts, APOE-high (H) showed significantly shorter PFS (median 9.2 vs 11.8 vs 13.0 months (mo), high vs low (as reference) logrank P = .0021) and OS (median 21.9 vs 35.8 vs 34.6 mo; logrank P = .0017) compared to APOE-median and -low, respectively. Opposite results were observed for DACH1, where DACH1-H tumors had longer PFS (median 14.5 vs 10.6 vs 8.07 mo; logrank P = .0011) and OS (median 39.4 vs 30.9 vs 21.5 mo; logrank P = .0021) when treated with cet. In bev-treated pts, similar results were observed with APOE-H showing shorter OS (median 25.8 vs 26.3 vs 37.5 mo; logrank P = .0016) and DACH1-H longer OS (median 36.5 vs 28.3 vs 22.4 mo; logrank P = .0017). No significant gene-treatment interaction was observed for either gene for PFS and OS. Conclusions: The tumor expression of metabolic genes associated with changes in the brain structure was prognostic in mCRC pts treated with first-line therapy. Notably, APOE and DACH1 have been recently reported to play a role in CRC where APOE overexpression has been associated with aggressive biological behavior whereas DACH1 has been shown to suppress CRC cell growth and invasion. Our results support this evidence and suggest that further investigation into the role of APOE and DACH1 in CRC biology and into their potential as targets for drug development is warranted. Trial Identifier: NCT00265850.

3523 Background: Evidence suggests neurotransmitter signaling may play a crucial role in tumorigenesis of gastrointestinal (GI) cancers, including migration, proliferation, and apoptosis, as well as angiogenesis and the microenvironment. We developed and applied a strategy to identify upstream regulators of neurotransmitters and their associations with patient outcomes. Methods: Prior literature yielded 85 neurotransmitter signaling genes mapped to RNA-seq gene expression in tumor tissue from 545 patients with mCRC enrolled in the phase III CALGB/SWOG 80405 trial. These samples were also sequenced by FoundationOne CDx for DNA damage. Using Cox proportional hazards regression, we identified a subset of CDx genes associated with overall survival (OS) or progression-free survival (PFS). We extended the Causal Inference Test (CIT) for time-to-event data and identified a subset of the 85 signaling genes consistent with mediation of DNA mutation effects on OS and PFS. Another CIT analysis identified potential upstream neurotransmitter regulators, gene expression mediators of mutation effects on the signaling genes. Top genes were then assessed in whole-transcriptome sequencing (WTS) expression data with Caris MI profile collected from 398 patients with advanced CRC enrolled in the MONSTAR-SCREEN-2 trial. Results: At the 0.05 alpha level, we identified 20 signaling genes with gene expression associated with PFS and/or OS, and 68 genes with evidence of DNA mutations associated with PFS and/or OS. False discovery rate (FDR) < 0.05 was applied to filter the 56,674 expression features on PFS and OS associations, yielding 173 unique genes as possible mediators. The CIT yielded 53 putative mediators at FDR < 0.05, suggesting upstream regulation of neurotransmitter signaling. Five genes were identified as targeting at least 8 signaling genes each, PIGU, ANO9, LY6G6D, and GPR160, and FSCN1, where the first 4 are favorable and only FSCN1 is a poorer prognostic. Following up on these 5 genes in MONSTAR-SCREEN-2 by dichotomizing at the median value of WTS expression, 3 were nominally associated with OS, PIGU ( P = 0.050; HR, 0.59; 95%CI, 0.34-1.00), ANO9( P = 0.029; HR, 0.55; 95%CI, 0.32-0.95), LY6G6D( P = 0.0024; HR, 0.44; 95%CI, 0.25-0.76), and FSCN1 was suggestive ( P = 0.079; HR, 1.62; 95%CI, 0.94-2.77), with direction of effects in agreement with 80405 results for all four. Conclusions: Our novel approach identified previously unknown upstream regulators of neurotransmitter signaling associated with treatment outcomes in mCRC. PIGU, FSCN1, and LY6G6D have been suggested in prior literature as targets for CRC and ANO9 has been suggested as a target for GI cancer. These results bolster the strategy of using mediation analysis with large-scale molecular data to identify new therapeutic targets in CRC. NCT00265850.