Peritoneal dissemination in early gastric cancer: importance of the lymphatic route.

The current paradigm concerning the mechanism of peritoneal dissemination of gastric cancer is that it occurs through an invasive process in which cancer cells directly penetrate the gastric wall and exfoliate into the peritoneal cavity. However, some experimental studies suggest the lymphatic route as an alternative. We present five early gastric cancer cases, which support this alternative pathway of peritoneal dissemination without direct invasion in the serosa. We investigated all patients with early gastric cancer who underwent curative gastrectomy between September 2002 and February 2015 at the Shizuoka Cancer Center, Japan. We examined them by intraoperative peritoneal lavage cytology and frozen section diagnosis of peritoneal nodules during laparotomy. Peritoneal dissemination was defined as peritoneal metastasis by positive cytology or histological diagnosis. Among 1509 early gastric cancers, five cases (0.3 %, 95 % CI 0.1-0.8 %) presented peritoneal dissemination detected by lavage cytology and frozen section diagnosis of peritoneal nodules. Histological examination revealed that the primary tumors invaded the submucosal layer using the lymphatic route, through which they metastasized to regional lymph nodes. Our data indicate that gastric cancer may give rise to peritoneal dissemination even at an early stage, probably through the lymphatic route without direct invasion into the serosa.