Red blood cells inhibit tumour cell adhesion to the peritoneum

Background: Perioperative blood transfusion has been associated with increa sed tumour recurrence and poor prognosis in colorectal cancer. Blood loss i n the peritoneal cavity might be a tumour-promoting factor for local recurr ence. The aim of this study was to investigate whether blood in the periton eal cavity affects local tumour recurrence. Methods: In an established in vivo rat model the effect of 1.5 ml syngeneic whole blood on tumour cell adhesion and tumour growth was investigated. In the same model the effect of 1.5 ml pure red blood cell (RBC) concentrate and 1.5 ml RBC-derived substances on tumour cell adhesion was studied. In a n established in vitro model the effect of increasing numbers of RBCs (0-25 0 x 10(6)) on tumour cell adhesion and tumour growth was assessed. Results: Both the presence of blood and RBC concentrate in the peritoneal c avity prevented tumour cell adhesion in vivo (overall P less than or equal to 0.001 and P less than or equal to 0.05 respectively), rather than promot ing adherence. RBC concentrate and RBC-derived substances had a comparable inhibitory effect on tumour cell adhesion. In in vitro studies RBCs inhibit ed tumour cell adhesion but not tumour growth. Conclusion: RBC-derived factors prevent tumour cell adhesion to the periton eum, and consequently tumour recurrence.