Marker proteins as indicators of tumour response to therapy

Serological markers which are secreted products of tumour cells have the potential to provide an indicator of viable tumour mass. In practice their ability to do this depends on a variety of factors which include specificity, mode of metabolism and concentration in relation to viable tumour bulk and assay sensitivity. In general, eutopic products have proved more useful than ectopic products which with few exceptions tend to be produced in only small concentrations even in advanced disease states. Human chorionic gonadotrophin produced by choriocarcinoma remains the most effective marker for any human tumour. For more than 20 years this marker has provided a reliable guide to the course of the disease and the response to therapy. There is a clear distinction between therapy which is ineffective and that which is effective in terms of marker concentration. The limitations of this substance and other tumour markers as indicators of response to therapy will be discussed.