Ploidy and imprinting in hydatidiform moles: Complementary use of flow cytometry and immunohistochemistry of the imprinted gene product p57 ^KIP2 to assist molar classification

OBJECTIVE: To determine whether the combination of flow cytometry and immunohistochemistry for p57 expression is useful for the pathologic classification of diagnostically challenging hydatidiform moles. STUDY DESIGN: Six probable hydatidiform moles that were difficult to classify pathologically were reevaluated by histology, flow cytometry and immunohistochemistry for p57. RESULTS: In all cases, the pathologic diagnoses were easily resolved: two cases were partial moles (triploid, p57 positive), two cases were early complete moles (diploid, p57 negative), and two cases were twin gestations with normal villi (diploid, p57 positive) admixed with villi from a complete hydatidiform mole (diploid, p57 negative). CONCLUSION: Immunostaining for the paternally imprinted, maternally expressed p57 gene product is a practical and accurate adjunct to flow cytometry in the pathologic classification of hydatidiform moles.