The interpretation of marker protein assays: a critical appraisal in clinical studies and a xenograft model.

Although useful in the management of malignant testicular tumours, alphafoetoprotein and human chromonic gonadotrophin are not perfect parameters of tumour bulk. In a series of 65 patients with marker-positive advanced disease, 23 showed the phenomenon of discordance of markers or dissociation from tumour response. Transplantable human malignant teratoma xenografts were established in immune-suppressed mice as models of the human disease. In the model system, it was demonstrated that tumour AFP concentration was reflected by AFP titres in the blood, but that tumour AFP (or blood AFP) did not correlate well with tumour size. One xenograft line illustrated the evolution of marker-negative tumour cells from a patient who was initially AFP-positive.