Choriocarcinoma. A model for tumour markers.

Human chorionic gonadotrophin (hCG) was the first major tumour marker to be identified and in gestational choriocarcinoma remains the closest we have to the ideal indicator of tumour activity. What is measured in assays for this substance is however a complex subject which has to be understood if misinterpretation of the data is to be avoided. It is also necessary to understand the pathology and natural history of the spectrum of hCG producing tumours. The distinction between luteinising hormone (LH) and hCG only became possible with the production of antisera predominantly directed at the beta subunit of hCG. Since then monoclonal antibodies directed at restricted epitopes have revealed that a range of hCG fragments contribute to what is measured. Within the spectrum of hCG producing lesions are those that are self-terminating whilst others are premalignant, malignant but responsive to chemotherapy, or refractory to all present agents. Awareness of this complexity is essential for interpretation of values. For patients with hydatidiform mole hCG measurements form the basis of identifying progressive lesions and thus constituting a still unique biochemical screening programme for cancer. Its roles in diagnosis, prognostication, monitoring the course of the disease and in follow-up for detection of recurrence are unique in many respects. Although hCG measurements provide information critical to the management of each of these lesions that information can only be properly understood through an understanding of the pathological entities involved and the pharmacokinetics of hCG metabolism and excretion.