Limitations of using pregnancy-associated alpha-2 glycoprotein as a tumour marker

The development of a new enzyme-linked immunoassay for pregnancy-associated alpha-2 glycoprotein (alpha 2-PAG) has provided an opportunity to reassess the value of this protein as a tumour marker. Serum samples from 800 healthy individuals and patients with various benign and malignant diseases were assayed. There was a very wide range of alpha 2-PAG levels in normal females (1- greater than 100 mg/l), and although the levels found in normal males were lower and better defined, this intrinsic variation between individuals makes a single determination in a tumour-bearing patient meaningless. Also, the levels of alpha 1-PAG in patients with advanced cancer were not significantly different from levels in localized cancer, benign disease or even healthy controls, and furthermore, levels before and after successful cancer treatment did not show a significant change. Our results therefore indicate that alpha 2-PAG is unsuitable for use as a tumour marker as there was no apparent relationship between the levels of alpha 2-PAG and either tumour burden or response to treatment.