Fig. 15: Mosaic conceptions.

a Nonmolar mosaic conception is composed of hydropically enlarged villi that have somewhat cellular stroma and trophoblastic inclusions but lack trophoblastic hyperplasia. b Villi demonstrate a discordant pattern of p57 expression, with positive cytotrophoblastic cells and negative villous stromal cells (this was seen throughout the stained section). Genotyping demonstrated paternal:maternal allele ratios enriched for paternal alleles. c, d Molar mosaic conception has two distinct villous components. Villi with features of an early complete hydatidiform mole are focally present (c, left portion and d), whereas other villi have some irregular shapes and hydropic change but lack trophoblastic hyperplasia (c, right portion). e, f p57 immunostain highlights the different components, with discordant p57 expression in nonmolar mosaic component manifested as p57-positive cytotrophoblastic cells and p57-negative villous stromal cells (e) and lack of p57 expression in molar villi (f) (see Lewis et al. [35] for examples of genotyping data).