MECHANISMS OF THE FORMATION OF THE PERITONEAL DISSEMINATION IN GASTRIC-CANCER

To clarify the mechanisms of the formation of peritoneal dissemination , a new animal model by the i.p. inoculation of highly metastatic gast ric cancer cell line MKN-45-P was developed. Peritoneal dissemination with bloody ascites was found in 100% of nude mice, injected 1x10(7) M KN-45-P cells in suspension into the peritoneal cavity. By a highly se nsitive method for specific detection of metastasized human tumor cell s in nude mice using polymerase chain reaction, a human beta-globin-re lated sequence in the DNA from various parts of the peritoneum was spe cifically amplified and detected by gel electrophoresis and by a speci fic oligonucleotide probe. Greater omentum showed a strong signal of t he amplified fragments of human beta-globin gene from the 1st day and the signals gradually increased. The signals in the gonadal fat, mesen tery and ovarium could be weakly detected on the Ist day, transiently decreased on the 3rd day, and then increased from the 7th day. In the diaphragm, and abdominal wall, signals could be detected from the 7th day. In contrast, small intestine and colon did not show any human bet a-globin signals. In greater omentum and gonadal fat, cancer cells wer e selectively detected in the milky spots stained by activated carbon on the 3rd day. In the diaphragm, cancer cells adhered to the small po res termed stomata, and invaded into the subdiaphragmatic lymphatic la cunae connected with stomata. From the 3rd day, mesothelial cells of t he abdominal cavity became round and separated, resulting in the expos ure of the underlying connective tissue. MKN-45-P cells were found to adhere to the naked areas of the submesothelial connective tissue. Fro m these results, we conclude that the major metastatic route of the pe ritoneum may be firstly through milky spots, secondly through the diap hragmatic stomata, and thirdly by the adhesion to the naked connective tissue exposed after shrinkage of the mesothelial cells. The third pr ocess may be related to the interaction between some adhesion molecule s and their ligands.