Plasma blood group changes in gastrointestinal tract carcinoma.

The levels of A, H, I, and i plasma antigens and of anti-B, anti-I, and anti-T antibodies were measured in 70 subjects with colonic or gastric carcinoma. These studies showed a significant increase in A plasma activity of the A subjects, and in H plasma activity of the O subjects, while 25% of the tested subjects showed increased I plasma activity. There was no difference in i plasma activity between cancer patients and healthy subjects. These results take into account the marked polymorphism acquired by neoplastic tissue, which is capable also of producing a greater quantity of antigens than that of healthy subjects. Nevertheless this heterogeneity forms a barrier to the clinical measurement of these plasma antigens for screening neoplasms. The significant fall in the amount of anti-T antibodies seemed to be secondary to the absorption of these antibodies on the surface of the tumour cells.