P57KIP2 immunostaining and molecular cytogenetics: combined approach aids in diagnosis of morphologically challenging cases with molar phenotype and in detecting androgenetic cell lines in mosaic/chimeric conceptions.

Although molar pregnancies are typically defined by morphological, histologic, and genetic criteria, most cases are diagnosed solely on histologic findings. Recently, several studies have demonstrated the usefulness of p57KIP2 immunostaining as an ancillary diagnostic tool for molar pregnancies. The p57KIP2 gene is paternally imprinted and maternally expressed; therefore, the positive staining of its protein indicates the presence of a functional maternal allele. Because complete hydatidiform moles (CHMs) lack a maternal genome, p57KIP2 immunostaining is absent. Previous studies have validated this staining technique by demonstrating differential nuclear expression in CHMs versus non-CHMs; however, these studies have not included cytogenetic analysis. We report on 58 cases of hydropic placentas, correlating cytogenetic and p57KIP2 immunostaining results. In addition, cases with unusual p57KIP2 staining patterns are discussed. Also included are 2 mosaic conceptions (1 diploid/triploid and 1 diploid/tetraploid), 6 chimeric/mosaic conceptions with androgenetic/biparental cell lines, and 2 cases of placental mesenchymal dysplasia.