Use of gene expression profiling to examine association between MUC1 and claudin 18 in gastrointestinal cancers: Implications for targeted therapies.

838 Background: Gastrointestinal tract cancers exhibit considerable molecular heterogeneity, which requires a detailed understanding of their distinct genetic profiles. Understanding the gene expression of other genes along with Claudin 18 (CLDN18) could provide insights into their interactions. Methods: We conducted a retrospective analysis of NGS profiling on 1,043 GI cancer tissue samples from three cohorts: Upper and Lower Gastrointestinal Cancer Cohort (GICC; n=651), Pancreaticobiliary Cancer Cohort (PBCC; n=316), and Hepatocellular Carcinoma Cohort (HCC; n=76). Immunohistochemistry data for PD-L1, Her2 and MMR proteins, NGS based Tumor mutation burden (TMB) and gene expression profiling (GEP) of 20,802 genes including CLDN18 was examined in a subset by targeted transcriptome profiling. We explored associations of these biomarkers with expression of CLDN18. Results: In GICC, frequent mutations were seen in TP53 (68%; 442), APC (33.5%; 218) and KRAS (33.3%; 217). PBCC, showed mutations in TP53 (62%; 197), KRAS (47%; 149) and CDKN2A (16%; 51). HCC showed mutations in TP53 (42%; 32), ARID1A (18%; 14) and KRAS (9%; 7). Amplifications were predominantly observed in MYC (13%; 120), ERBB2 (5%; 49) and CCND1 (5%; 44). Fusions were infrequent. All MSI-H cases (11/462; 2.4%) were observed in GICC. High TMB (≥10 muts/mb) was seen in 23% (111/481), stratified as 28% (90/318) in GICC, 13% (18/139) in PBCC and 10% (3/30) in HCC. Out of 321 samples analyzed for gene expression profiling, CLDN18 was significantly upregulated in 65 (20%) samples. The expression of CLDN18 did not show statistically significant correlation with Her2 (n=184), PD-L1 (n=231), TMB (n=228), or MSI (n=229); (p>0.05). In subset where both CLDN18 and MUC1 expression were analyzed (n=118), all the CLDN18 positive tumors showed overexpression of MUC1. This finding was statistically significant (p<0.05). Increased expression of MUC1 promotes cancer cell mobility promoting metastases. Expression of MUC1 can play an important role in the development of resistance to chemotherapy. MUC1 expression in cancer cells is associated with avoidance of immune defenses. Thus, this finding of CLDN18 and MUC1 association is especially relevant as the CLDN18 targeted therapies may be the potential avenue for the aggressive and chemo-resistant MUC1 expressing tumors. Conclusions: This study identifies potential association between MUC1 and CLDN18. GEP could enhance biomarker detection and support personalized treatment approaches. Future research should integrate these findings with clinical data to improve precision in GI cancer care.