Background: Peritoneal spread of tumour cells is a major source of morbidity and mortality in patients with colorectal cancer. In order to develop strategies to prevent intraperitoneal dissemination and to treat peritoneal carcinomatosis, the spread of tumour cells in the peritoneal cavity was studied. Methods: Two million CC531 colon carcinoma cells were administered intraperitoneally in five groups of eight rats. The rats were killed after 1, 2, 4 and 8 hours and 3, 7, 14 and 21 days. After inspection of the abdominal cavity, samples of blood and ascites were taken. Liver, spleen, omentum, mesentery, diaphragm, parathymic lymph nodes and lungs were removed for histology and immunohistochemistry. Results: No abnormalities were seen in the abdominal cavity until day 3. Subsequently the peritoneum and omentum became thickened and after 21 days all rats had haemorrhagic ascites and peritoneal carcinomatosis. The abdominal fluid contained tumour cells at all stages. The number of tumour cells decreased in the first 8 hours, and increased thereafter. At microscopy the peritoneum was completely covered by tumour cells after 3 days. Tumour I cells concentrated in the milky spots (MS) of the omentum within 4 hours. The size of the MS increased as a result of an increase in number of tumour cells and macrophages. After 7-21 days the MS were completely replaced by tumour cells and new MS were formed. In the diaphragm tumour cells invaded the lymphatic lacunae after 8 h, and obliterated these after 3-7 days. Also invasion of the muscle fibres was seen after 3 days. Microscopically no tumour cells were found in blood, liver, spleen, parathymic nodes and lung. Conclusion: After intraperitoneal administration of CC531 colon carcinoma cells, tumour cells spread throughout the abdominal cavity, and concentrate in the milky spots of the greater omentum, the paracolic gutters, the subhepatic and subphrenic spaces and in the lymphatic lacunae of the diaphragm. (C) 2001 Harcourt Publishers Ltd.
