<qa>  What is the hCG beta molecule that is a characteristic of trophoblastHuman choriogonadotropin belongs to a family of heterodimeric glycoprotein hormones which are comprised of two noncovalently bonded subunits with four N-linked carbohydrates. During chemotherapy, the hCG beta molecules can be degraded. A study has been reported by crystallographic analysis by which they found that crystals of deglycosylated human chorionic gonadotropin has a hexagonal bipyramidal structure using a method of vapor diffusion against ammonium sulfate. Previously, conformation of the hCG molecule has rarely been studied. By chemical method, over glycosylated hCG has been reported to be a characteristic of trophoblastic cancer, but its clinical utility remains to be established. Photoelectric method is a newly developed method to study the conformation of the protein or glycoprotein molecules. As yet, there is no report about the conformation of hCG serial studies. Gestational trophoblastic tumor as well as other gynecological cancers often underwent antitumor chemotherapy and monitor by tumor markers. During the antineoplastic chemotherapies, the conformational change of tumor markers, including hCG beta in persistent gestational trophoblastic tumor for cancer and its clinical meaning has only been rarely studied. Up to the present time, it is still not well understood whether a conformational change or reduced stability of the heterodimer may occur during chemotherapy. 