New concepts in trophoblastic growth and differentiation with practical application for the diagnosis of gestational trophoblastic disease.

Human trophoblast in normal implantation and placentation appears to undergo two different pathways of differentiation resulting in the development of villous and extravillous trophoblast. Cytotrophoblast (CT) differentiates abruptly into syncytiotrophoblast (ST) on the villous surface as compared with the spectrum of differentiation exhibited by extravillous trophoblast where CT differentiates into intermediate trophoblast (IT) and then into multinucleated intermediate trophoblastic cells (MITC). The various types of gestational trophoblastic lesions can be defined and related to discrete pathologic aberrations occurring at different stages of trophoblastic differentiation. The rapid advance in the discovery of new trophoblastic markers has facilitated the molecular dissection of the lineage and differentiation stages of trophoblast and related these to various trophoblastic lesions. Furthermore, antibodies against these markers, especially those that are able to recognize formalin-resistant epitopes, have considerable value in the study and differential diagnosis of different types of gestational trophoblastic disease.