Candidate molecular alterations associated with potential resistance in KRAS G12D gastrointestinal cancers.

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3519 Background: KRAS G12D commonly occurs in pancreatic (PDAC) and colorectal (CRC) cancers. Though developing KRAS G12D inhibitors is pertinent, it is expected that primary and acquired resistance will limit efficacy, similar to those seen with KRAS G12C inhibitors. Here, we assessed the prevalence and outcomes of candidate mutations co-occurring with KRAS G12D in PDAC and CRC using liquid biopsy data. Methods: Patients with advanced CRC and PDAC tested with Guardant360 genomic profiling from 2020 to 2023 (~2500 & 3500 samples) were included. Candidate resistance mutations were determined based on mutations reported following KRAS G12C inhibition. Patients with advanced CRC and PDAC tested with Guardant360 at Mayo Clinic (2016-2023) (1158 & 904 samples) were assessed for overall survival (OS). Patients were divided into three groups: KRAS G12D alone, KRAS G12D with candidate resistance alterations, and KRAS G12D not detected (ND). OS was estimated using Kaplan-Meier method. Cox regression was used for multivariable survival analyses. Results: The Guardant360 database reported KRAS G12D in 16.5% of CRC and 40.2% of PDAC samples. The Table below summarizes the most frequent candidate resistance alterations co-occurring with KRAS G12Dincluding point mutations of KRASand PIK3CAand amplifications of EGFR, KRAS, BRAFand MYC. In the Mayo cohort, 8.9% of CRC and 23.5% of PDAC patients had KRAS G12D. In CRC, those with KRAS G12Dand ≥1 candidate resistance alteration had a significantly lower OS (mOS 18.7m) than KRAS G12D alone (30.9m), and ND (37.3m) ( p=0.004). The presence of concurrent candidate resistance alterations with KRAS G12D remained a poor prognostic factor with HR 2.1 (95% CI: 1.3 – 3.2, p=0.001) after adjusting for age and other patient characteristics. Similarly, in PDAC, those with KRAS G12D and ≥1 resistance mutation had significantly lower OS (mOS 8.1m) than KRAS G12D alone (10.5m) and ND (16.1m) (p<0.0001). In multivariable analyses, both KRAS G12D with candidate resistance alterations (HR 2.1, 95% CI: 1.4-3.3, p<0.001) and G12Dalone (HR 1.6; 1.3–2.0, p<0.001) were poor prognostic factors. Among patients with serial Guardant360, treatment response trended with KRAS G12D variant allele frequency. Conclusions: Circulating tumor DNA testing is a useful tool to reveal candidate molecular alterations linked to potential resistance to KRAS G12D targeting in patients with KRAS G12D gastrointestinal cancers. KRAS G12D with these concurrent molecular alterations is a poor prognostic factor in both PDAC and CRC. [Table: see text]