In vivo and in vitro studies on nonspecific blocking factors of host origin in cancer patients. Role of plasma exchange as an immunotherapeutic modality.

Experimental and clinical data are reviewed on elevated glycoprotein levels in tumor-bearing animals and patients at various stages of disease advancement. The authors report their findings in 232 patients with various solid tumors; these confirm and extend the reports in the literature. It is shown that some of these glycoproteins, rich in sialic acid, exhibit immunosuppressive properties in vitro, and it is suggested that tumors may protect themselves by triggering hepatic synthesis of sialoglycoproteins which "coat" the binding sites of both immunocompetent cells and tumor cells and thereby abrogate recognition and killing of the latter by the immune system. This concept of nonspecific blocking factors of host origin has already been substantiated to some extent by observations on the consequences of plasma exchange in 24 patients with metastatic tumors; eight of these patients exhibited an objective tumor regression. It is suggested that such studies should be extended to postoperative patients and that circulating sialoglycoprotein assays could be one of the ways of monitoring tumor growth, including growth during the nonvisible phase.