Risk factors for peritoneal recurrence in serosa-negative gastric cancer.

19 Background: Peritoneal recurrence is often observed in gastric cancer patients without serosal invasion. It is difficult for pathologists to evaluate whether tumor cells penetrate serosa or not, because the subserosa layer is very thin. We evaluated the incidence and risk factors of peritoneal recurrence in serosa -negative gastric cancer patients to clarify the mechanism of peritoneal recurrence in these patients. Methods: A total of 1,745 gastric cancer patients underwent R0 resection from 2002 to 2009 were enrolled. The incidence of peritoneal recurrence according to tumor depth was analyzed. In serosa-nagative patients, the univariate and multivariate analysis were performed to identify the risk factors for peritoneal recurrence. Results: Peritoneal recurrence was observed in 64 (3.7 %) out of 1,745 patients. The incidence of peritoneal recurrence according to depth of tumor invasion was in 0 / 466 in T1a, 5 / 567 (0.88 %) in T1b, 4 / 187 (2.1 %) in T2, 31 / 360 (7.9 %) in T3, 20 / 108 (15.9 %) in T4a, and 4 / 12 (25 %) in T4b, respectively (p<0.001). As for the risk factor for peritoneal recurrence in T3 patients, histologically undifferentiated type, negative lymphatic invasion, scirrhous type, invasive infiltrating growth pattern were the significant factors identified by univariate analysis. Only the invasive infiltrating growth pattern (OR3.44 p0.038) was selected as significant independent risk factor for peritoneal recurrence by multivariate analysis. In T1b / T2 patients, massive lymph node metastasis (N3a, 3b), scirrhous type were the significant factor for peritoneal recurrence by univariate analysis. Only massive lymph node metastasis (OR25.1 p<0.001) was selected as the significant independent risk factor by multivariate analysis. Conclusions: The incidence of peritoneal recurrence increases in proportion to the tumor depth. Invasive infiltrating growth pattern was selected as an independent risk factor for peritoneal recurrence in T3 patients, while it was massive lymph node metastasis in T1b / T2 patients. The results suggest the possibility that microscopic serosal invasion in T3 tumor and lymphatic progression in T1b / T2 tumor may contribute to peritoneal recurrence in gastric cancer.