In a series of gastric cancer patients twenty-eight percent of the primary tumors expressed high levels of the Lewis carbohydrate. This correlated significantly with clinicopathological parameters of advanced disease (tumor size of > 50 mm, M1 stage, UICC stage IIIB/IV). In multivariate analysis, high Lewis expression was found to be a new independent factor of poor prognosis. In addition, Lewis was expressed on solid metastases and micrometastatic cells originating from Lewis positive primary tumors. The data suggest that Lewis positive tumor cells may have an advantage in penetrating secondary organs because, like leukocytes, they can specifically adhere to activated vascular endothelia.