Clinical utility impact of DNA-based cytology using droplet digital methylation-specific PCR in gastric cancer.

[BACKGROUND] Peritoneal dissemination is a major cause of poor prognosis in gastric cancer (GC). Although conventional peritoneal lavage cytology (CY) is used to detect micrometastatic peritoneal spread, its sensitivity is limited. This study aimed to evaluate the clinical utility of droplet digital methylation-specific PCR (ddMSP) targeting cancer-specific methylation for DNA-based detection of peritoneal dissemination.

[METHODS] Peritoneal lavage fluid was prospectively collected from 400 samples in 357 GC patients, including 360 samples from 339 patients with chemotherapy-naïve tumors. DNA was extracted, bisulfite-converted, and analyzed by ddMSP targeting CDO1 and HOPX methylation. Diagnostic performance was assessed by ROC analysis, and associations with clinicopathological features and prognosis were evaluated using logistic and Cox regression models.

[RESULTS] CDO1 and HOPX methylation levels were significantly elevated in CY1 cases compared with CY0 (p < 0.0001). CDO1 methylation demonstrated excellent diagnostic accuracy for CY1 (AUC: 0.93; sensitivity: 83.9%; specificity: 90.9%), while HOPX methylation showed slightly lower performance (AUC: 0.86). Multivariate analysis revealed that ddMSP CDO1-hi was independently associated with serosal invasion (pT4), and HOPX-hi with both pT4 and nodal metastasis. Furthermore, CDO1-hi status was an independent adverse prognostic factor for peritoneal dissemination-free survival (HR: 2.73, p = 0.018).

[CONCLUSIONS] ddMSP-based detection of CDO1 methylation provides a sensitive and specific method for identifying micrometastatic peritoneal spread in GC. This DNA-based approach may serve as a valuable prognostic biomarker and contribute to improved perioperative management in gastric cancer.