A 28-year-old woman has an intrauterine molar pregnancy removed by suction curettage. On histology the specimen shows hydropic villi with circumferential (360°) trophoblastic proliferation, no fetal parts, p57 (CDKN1C) immunostaining negative in villi and cytotrophoblasts. What is the diagnosis and chromosomal constitution?
- A Partial hydatidiform mole; 69,XXY
- B Complete hydatidiform mole; 46,XX (androgenetic) ✓
- C Invasive mole; 46,XY (biparental)
- D Placental site trophoblastic tumour; diploid
Explanation
p57 (CDKN1C) is a maternally imprinted, paternally expressed gene. In complete hydatidiform moles (androgenetic diploid — 46,XX or 46,XY — arising from fertilisation of an anucleate egg by one or two sperm), there is NO maternal genetic contribution, so p57 is NOT expressed → staining is NEGATIVE in villous cytotrophoblasts and stromal cells. In partial moles (triploid with maternal contribution), p57 is positive. Complete moles have circumferential trophoblastic hyperplasia, no embryo/fetus, and swelling of virtually all villi. The distinction is critical because complete moles carry a ~15–20% risk of gestational trophoblastic neoplasia.
Reference: Williams Obstetrics, 26th ed.
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Written and medically reviewed by the StethoPrep medical team.