Objective: To determine the optimal cutoff value of  carcinoembryonic antigen (CEA) mRNA level for detection of  free cancer cells (FCC)  in peritoneal washes with realtime PCR and its clinical significance.
Methods: The CEA mRNA levels in peritoneal washes from 65 cases of gastric cancer were detected by realtime RTPCR. After 5year followup, cutoff value of CEA mRNA level was obtained with the ROC curve analysis and the relationship between FCC and prognosis with KaplanMeier method was studied.
Results: (1)With the ROC curve analysis, if the cutoff value of CEA mRNA level was31.21,the Youden’s index was the  highest.(2)The mean survival time (months) in group of FCC(+),(-)was 17.2 and  48.7 months respectively, The median survival was 8.1 and 60.0 months, respectively, with significant difference (P= 0.000).The 5year survival rate was  9.1% and67.4%，respectively. Compared with FCC(+) group, the FCC(-) group had significantly extended life span. COX regression showed that FCC was an independent prognostic factor.
Conclusions: (1) Our results suggest that the best cutoff value of CEA mRNA levels for detection of FCC in peritoneal washes is 31.2 copies/mL; (2) This study shows that FCC is an independent factor that affects prognosis. FCC(+) denotes the presence of intraoperative tumor dissemination and predicts a poor prognosis.