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Background and Aims: Colorectal tumors can be classified based on their growth pattern into the polypoid growth-type (PG-type) and non-polypoid growth-type (NPG-type). To ascertain whether there is any relationship between the expression of particular blood group-related antigens (A, B, H, Lewis (Le)a, sialyl Le(a), Le(x), sialyl Le(x)) in a colorectal tumor, and a tumor having polypoid or non-polypoid growth, we examined 78 PG-type and NPG-type colorectal cancers., Methods: Fourteen PG-type and 64 NPG-type colorectal carcinomas were subjected to immunohistochemical analyses by using monoclonal antibodies against A, B, H, Le(a), sialyl Le(a), Le(x) and sialyl Le(x)., Results: The patients with NPG-type carcinomas had a significantly younger age of onset, significantly smaller maximal tumor diameter, significantly higher rate of lymph node metastasis and significantly worse prognosis than those with PG-type carcinomas. Among the 32 tumors of patients with blood type A or AB, isoantigen A was expressed in a significantly larger percentage of NPG-type carcinomas than PG-type carcinomas (95.8 vs 62.5%, respectively; P=0.014). Among all 78 tumors, sialyl Le(x) antigen was expressed in a significantly larger percentage of NPG-type than PG-type carcinomas (90.6 vs 64.3%, respectively; P=0.010). Multivariate analysis using the logistic regression model revealed that isoantigen A and sialyl Le(x) expression were independent predictive risk factors for the development of NPG-type colorectal carcinoma., Conclusions: These data suggest that the expression of isoantigen A and sialyl Le(x) in a colorectal carcinoma partially determines whether the tumor will have polypoid or non-polypoid growth.