Role of milky spots as selective implantation sites for malignant cells in peritoneal dissemination in mice

We investigated the significance of milky spots for malignant cells in peritoneal dissemination using three mouse carcinomatous peritonitis models. P388 leukemia and Colon 26 cancer cells were labeled with bromodeoxyuridine (BrdU) and mice were inoculated intraperitoneally. After 24 h the greater omentum and the mesenterium were removed and stained immunohistochemically with anti-BrdU antibody. The labeled cells were found to have preferentially infiltrated into the milky spots in these specimens. Next, using B16 PC melanoma cells, which can be easily distinguished from the other cells by the intrinsic black melanin, the distribution of the melanoma cells was observed macro- and microscopically following intraperitoneal inoculation. The melanoma cells were similarly found to have selectively infiltrated into the milky spots in the omentum and mesenterium after 1 day. Moreover, the melanoma cells were growing and forming distinct metastic lesions within the milky spots 1 week later.