Studies with choriocarcinoma and normal pregnancy serum chorionic gonadotrophin

Serum obtained from either normally pregnant women or those with choriocarcinoma was pooled and purified by ammonium acetate/alcohol extraction followed by ionic exchange and gel filtration chromatography. The CG activity was monitored using a double antibody radioimmunoassay utilizing anti hCG both as the labelled ligand and standard. Biological activity was measured by the rat luteal cell radioreceptor assay. Both purified preparations exhibited heterogeneity in terms of the behaviour during ionic exchange chromatography and isoelectric focussing. The Stokes radii were 33A and 33.3A for normal pregnancy and choriocarcinoma hCG respectively. Material from both sources focussed between pH 4.5 and 5.5. Relative to the second international hCG standard the immunological activity of normal pregnancy hCG was 9,100 iu/mg and that of choriocarcinoma CG was 10,970 iu/mg. The corresponding biological potencies were 8,190 iu/mg and 7,569 iu/mg respectively. There was a significant difference between the biological to immunological activity of choriocarcinoma hCG (0.69) when compared with that of normal pregnancy CG (0.90). This was confirmed with a subsequent follow up study when individual serum samples from normal pregnancy were compared with those from choriocarcinoma patients (p = 0.01). It was concluded that in a third world situation this significant difference in the ratio of biological to immunological activity may be a useful method for evaluating treatment of choriocarcinoma patients.