Problems of interpretation of serum concentrations of alpha-foetoprotein (AFP) in patients receiving cytotoxic chemotherapy for malignant germ cell tumours.

Serial determinations of serum alpha-foetoprotein (AFP) concentrations are well established in monitoring the response to therapy of malignant germ cell tumours. Using a radioimmunoassay (RIA) with a sensitivity down to 2kul-1 the majority (57%) of 28 patients with non-AFP producing germ cell tumours had measurable immunologically-reactive AFP in their serum while on treatment. Follow-up for 11-43 months (mean 27) without evidence of tumour activity indicated that this immunologically-reactive AFP was unlikely to be produced by tumour. In patients where the initial serum AFP was raised prior to chemotherapy the AFP concentration did not fall to the normal range at the end of the treatment in 16 (32%) of 41 patients. Follow-up of these patients for 9-48 months (mean 27) has resulted in 5 (12%) relapses in this group. Serum AFP greater than 20kul-1 three months after stopping chemotherapy was a good indicator of residual active tumour and 4 (57%) of 7 patients in this group relapsed. The production of detectable serum AFP is probably related to the type of chemotherapy used and only 7 (14%) of 51 patients treated for gestational choriocarcinoma had detectable AFP concentrations while on cytotoxic chemotherapy. The problem of interpretation of serum AFP concentration in patients with malignant germ cell tumour stresses the need to determine whether there are differences between AFP produced by germ cell tumours and that produced at other sites as a basis for a sensitive assay system able to discriminate between them.