Transcriptional Signatures of Field Cancerization in Gastric Cancer
The high rate of local recurrence in gastric adenocarcinoma (GA) suggests that carcinogenesis is not a focal event but a field-wide process. This phenomenon, known as "field cancerization," posits that histologically normal peritumoral tissue is, in fact, a pre-neoplastic field harboring incipient molecular alterations that confound genomic studies using it as a normal control. To overcome this limitation, we performed a three-way comparative transcriptomic analysis of tumor, peritumoral, and true-normal gastric tissues using a deep learning framework. We identified a stable 138-gene signature established within the peritumoral field and conserved in the tumor, which was absent in healthy controls. Within this signature, three key COSMIC-listed driver genes were highlighted: the Hippo pathway component FAT4 and the p53-inhibitor MDM4 were upregulated, while the EMT-suppressor NDRG1 was repressed. Co-expression analysis revealed a dynamic rewiring of these drivers, with a significant positive correlation between FAT4 and MDM4 emerging exclusively in the peritumoral field. In contrast, a negative correlation between FAT4 and NDRG1 was observed specifically in the tumor context. In public cohorts, high expression of FAT4 and MDM4 was significantly associated with poor patient prognosis, whereas NDRG1 showed no prognostic association. Critically, the prognostic power of MDM4 was validated in our local patient cohort. Our findings demonstrate that the peritumoral field is a molecularly distinct state in gastric carcinogenesis, characterized by a metabolic shift, and identify FAT4 and MDM4 as key drivers of this early transition, with significant potential as prognostic biomarkers.