Objective: To detect promoter hypermethylation of the p16 gene in pre- and post-operative plasma, matched cancer tissues and para-tumor non-cancerous tissues of patients with gastric adenocarcinoma for evaluating the effectiveness of therapeutic intervention.
Methods: Primary tumor tissues and para-tumor tissues and preoperative plasma samples of 84 patients with gastric adenocarcinoma were collected, and 14-21 days' post-operative plasma of 30 of the 84 patients who underwent curative gastrectomy was available. Plasma of 15 healthy people was also collected as control. After sodium-bisulfite treatment, extracted DNA was amplified for p16 promoter hypermethylation by methylation-specific polymerase chain reaction (MSP). The PCR products were detected by both gel-ethidium bromide electrophoresis and high performance liquid chromatogram (HPLC).
Results: Among the samples from 84 patients, p16 hypermethylation was detected in 26 (31.0%) cancer tissues and 2 (0.02%) para-tumor non-cancerous tissues and 12 (14.3%) preoperative plasma, while plasma of the healthy people was negative. In all positive plasma, the paired primary tumor tissues were also confirmed to be methylated. As far as samples from 30 patients with post-operative plasma were concerned, 14 cancer tissues and 6 preoperative plasma samples were positive, and only 1 of 6 post-operative plasma remained hypermethylated. The results detected by HPLC exactly matched those by gel-ethidium bromide electrophoresis.
Conclusion: Promoter hypermethylation of the p16 gene detected in plasma consists with that in primary cancer tissues of patients with gastric adenocarcinoma. The alteration of status of hypermethylation of p16 in post-operative plasma is considered the consequences of surgical intervention. HPLC can be used as an efficient tool in detecting the product of MSP.