All of the following are examples of tumor markers, except-

Ans. is 'a' i.e., Alpha-HCG (a-HCG) Human chorionic gonadotropin (HCG) o HCG is a placental hormone. It is synthesized by the syncytiotrophoblasitc cells of the placental villi It is a glycoprotein It is a dimer and has two dissimilar subunits a Subunits b Subunits o But only the b subunit of HCG is typically measured as a tumour marker because of specificity of the b subunit o The b subunit of HCG has unique sequences that are not shared with other human glycoprotein hormones. It is detected by radioimmunoassay using antibodies to the b chain. o a HCG is not used as tumour marker because a unit of the FSH, LH and TSH are identical So there can be cross reactivity between a subunits of these hormone. o That is why in case of testicular tumours the patients also undergo simultaneous assay of LH to be ceain that the marker detected is PI HCG.