Hydatidiform moles: Ancillary techniques to refine diagnosis

Distinction of hydatidiform moles from nonmolar specimens and subclassification of hydatidiform moles as complete hydatidiform mole (CHM), partial hydatidiform mole (PHM), or early CHM are important for both clinical practice and investigational studies. The risk of persistent gestational trophoblastic disease and hence, clinical management, differs for CHMs, PHMs, and nonmolar specimens. However, diagnosis based solely on morphology suffers from poor interobserver reproducibility and remains problematic even for experienced gynecologic pathologists. The unique genetic features of CHMs (androgenetic diploidy), PHMs (diandric triploidy), and nonmolar specimens (biparental diploidy) allow for certain molecular techniques, including immunohistochemical analysis of p57 expression (a paternally imprinted maternally expressed gene) and molecular genotyping, to refine the diagnosis of hydatidiform moles. Although p57 immunostaining alone can identify CHMs, which lack p57 expression because of the lack of maternal DNA, this analysis cannot distinguish PHMs from nonmolar specimens as both express p57 because of the presence of maternal DNA. Short tandem repeat genotyping, which can determine the parental source of polymorphic alleles, can distinguish among all of these entities by discerning androgenetic diploidy, diandric triploidy, and biparental diploidy to rigorously diagnose CHMs, PHMs, and nonmolar specimens, respectively. An algorithmic approach using these techniques to refine morphologic diagnosis has been developed for routine practice. This review discusses current issues in the diagnosis of hydatidiform moles, including the limitations of morphologic diagnosis, the need for refined diagnosis to assure accurate ascertainment of risk of persistent gestational trophoblastic disease associated with the different subtypes of hydatidiform moles, the use of ancillary immunohistochemical and molecular techniques for providing such refined diagnosis, and problems that can be encountered with these techniques.