Subtitle: How p57 immunohistochemistry separates a complete mole from a partial mole and a hydropic abortus: the genetics, the histology, how to read the stain, a diagnostic algorithm, pitfalls, virtual slides and 10 MCQs.
Author: PathologyMCQ Editorial Board
Category: Gynaecological and Placental Pathology
Last Updated: October 2026
Read Time: 9 minutes
At-a-Glance
- p57 (CDKN1C) is paternally imprinted and maternally expressed, so it marks tissue that contains a maternal genome.
- Complete mole is androgenetic: villous cytotrophoblast and stromal cells are p57 negative.
- Partial mole and non-molar gestations both contain a maternal genome and are p57 positive; genotyping separates them.
- Read it correctly: ignore syncytiotrophoblast (always negative) and confirm the internal control in decidua or extravillous trophoblast.
Molar pregnancy is a form of gestational trophoblastic disease divided into complete and partial hydatidiform moles. The distinction matters because complete moles carry a much higher risk of persistent disease. Morphology alone can be difficult, especially early in gestation, and p57 immunohistochemistry is the most useful routine test.
Why p57 Works: The Genetics
p57 (CDKN1C) is a cyclin-dependent kinase inhibitor encoded on chromosome 11p15.5. The gene is paternally imprinted (the paternal allele is silenced) and maternally expressed. So p57 protein appears only in cells that carry a maternal genome.
Genetic origin → p57No maternal genome, no p57
Complete mole
Androgenetic diploid
PP
46,XX (usually one sperm duplicated in an empty ovum) or 46,XY (two sperm).
p57 lostPartial mole
Diandric triploid
PPM
69,XXY, 69,XXX or 69,XYY: two paternal sets and one maternal.
p57 retainedNon-molar gestation
Biparental diploid
PM
Normal or trisomic conceptus, including hydropic abortion.
p57 retainedPaternal set Maternal set
Histology of Complete and Partial Moles
Complete hydatidiform mole
- Diffusely enlarged, oedematous villi with central cisterns.
- Circumferential trophoblastic hyperplasia, often with atypia.
- Scalloped villous outlines; villous blood vessels and fetal parts are absent.
- Early complete mole (first trimester): bulbous, polypoid villi, hypercellular myxoid stroma with karyorrhectic debris and labyrinthine canaliculi, often without cisterns.
- Atypical implantation site with exaggerated, atypical extravillous trophoblast.
Partial hydatidiform mole
- Two populations of villi: large irregular villi with cisterns and small fibrotic villi.
- Irregular scalloped outlines with trophoblastic pseudoinclusions.
- Focal, mild trophoblastic hyperplasia.
- Fetal tissue or villous vessels with nucleated red cells may be present.
Complete mole vs partial mole vs hydropic abortus
| Feature | Complete mole | Partial mole | Hydropic abortus |
|---|---|---|---|
| Genome | Androgenetic diploid | Diandric triploid | Biparental diploid |
| Villi | Diffusely enlarged, cisterns | Two populations | Rounded, mildly hydropic |
| Trophoblast | Circumferential hyperplasia | Focal, mild hyperplasia | Polar, not hyperplastic |
| Outline | Scalloped | Scalloped, pseudoinclusions | Smooth |
| Fetal tissue | Absent | May be present | May be present |
| p57 (villous cytotrophoblast and stroma) | Negative | Positive | Positive |
Virtual Slides
Virtual slides · real casesComplete vs partial mole
Loading slide…
What to look for
Drag to pan · pinch or double-tap to zoom · use the + / − buttons
How to Read p57
Check the controlDecidua and extravillous trophoblast must be positive. If not, the stain has failed.
Ignore syncytiotrophoblastIt is p57 negative in every pregnancy.
Read the villiAssess nuclear staining in villous cytotrophoblast and stromal cells.
InterpretNegative villi = complete mole. Positive villi = partial mole or non-molar.
Complete mole: p57 negative
- Villous cytotrophoblast: negative.
- Villous stromal cells: negative.
- Decidua and extravillous (intermediate) trophoblast: positive, acting as the internal control.
Partial mole: p57 positive
- Villous cytotrophoblast: positive.
- Villous stromal cells: positive.
- Decidua and extravillous trophoblast: positive.
- The same pattern is seen in non-molar gestations, so a positive result does not prove a partial mole.
Summary Table: Interpreting p57
p57 by compartment
| Compartment | Complete mole | Partial mole | Non-molar gestation |
|---|---|---|---|
| Villous cytotrophoblast | Negative | Positive | Positive |
| Villous stromal cells | Negative | Positive | Positive |
| Syncytiotrophoblast | Negative | Negative | Negative |
| Extravillous trophoblast | Positive (control) | Positive | Positive |
| Decidua | Positive (control) | Positive | Positive |
Diagnostic Algorithm
Hydropic or abnormal villi on H&ECheck that the internal control is positive
↓ p57
Villi negativeComplete moleAndrogenetic; no genotyping needed
Villi positivePartial mole or non-molarUse morphology
↓
Still unsure?STR genotyping: diandric triploid = partial mole; biparental diploid = non-molar
↓
Discordant or patchy stainingThink twin or mosaic gestation → genotyping
Pitfalls in p57 Interpretation
1. p57 cannot separate partial mole from hydropic abortusBoth are positive. Trisomic hydropic abortions (for example trisomy 13, 18 or 21) can mimic a partial mole; genotyping resolves it.
2. Weak or patchy stainingTechnical problems can mimic loss. Always confirm a positive internal control before calling a complete mole.
3. The wrong internal controlUse decidua or extravillous trophoblast. Syncytiotrophoblast, blood clot and myometrium are not reliable controls.
4. Mosaic, twin or chimeric gestationsSome villi positive and others negative suggests a twin pregnancy (complete mole with a normal conceptus) or a mosaic conception. Genotype it.
5. Rare p57-positive complete molesRetention of maternal chromosome 11 can preserve p57 in an otherwise androgenetic mole. If morphology strongly suggests a complete mole, genotype.
6. Very early gestationEarly complete moles may lack cisterns and florid hyperplasia. Rely on the myxoid stroma clues and p57 rather than classic features.
Clinical Relevance
- p57 is most valuable when morphology cannot separate a complete mole from a partial mole or hydropic abortion.
- About 15–20% of complete moles progress to gestational trophoblastic neoplasia, compared with about 0.5–5% of partial moles.
- The diagnosis determines serial beta-hCG monitoring after evacuation.
Test Yourself: 10 MCQs
p57 and molar pregnancy: 10 MCQs
Imprinting, morphology, staining patterns and pitfalls. Tap an answer for the explanation.
Score: 0 / 10
More practice: the gynaecological pathology MCQ bank →
Exam Pearls
- p57 = maternal genome marker: complete mole negative, partial mole and non-molar positive.
- Read villous cytotrophoblast and stroma; syncytiotrophoblast is always negative.
- Decidua and extravillous trophoblast are the internal positive controls.
- Positive p57 does not prove a partial mole; genotyping separates it from a hydropic abortus.
- Discordant staining suggests a twin or mosaic gestation.
Featured course
Read every placental and gynae biopsy with a plan
Learn a pattern-based approach to products of conception, the endometrium and gynaecological tumours, so you know when a stain like p57 is needed.
Approach-Based Histopathology & Cytology
Pattern-based approaches for gynaecological pathology and every system
- Low-power algorithms for villi, endometrium and trophoblast
- Slide videos that walk you from pattern to diagnosis
- Built by practising pathologists for sign-out and exams
More courses
Preparing for an exam?
NEET-SS · DM · INI-SSNEET-SS / DM OncopathologyHigh-yield histopathology with full mocksView course →FRCPath Part 1FRCPath Part 1 HistopathologyNotes, MCQ/EMQ bank and 4 full mocksView course →FRCPath Part 2Ultimate FRCPath Part 2 Study ProgramShort surgicals, long cases and macro practiceView course →
The Pathology MCQ app
A slide and an MCQ every day
Daily MCQ with streaks, pinch-zoom virtual slides with annotations, and your courses in one place.
Get it onGoogle PlayComing soon to theApp Store
Related reads: Gynaecological pathology MCQs (WHO 6th edition) →
References
- Kurman RJ, Ellenson LH, Ronnett BM. Blaustein’s Pathology of the Female Genital Tract. 7th edition. Springer; 2019.
- Banet N, DeScipio C, Murphy KM, et al. Characteristics of hydatidiform moles: analysis of a prospective series with p57 immunohistochemistry and molecular genotyping. Mod Pathol. 2014;27:238–254.
- WHO Classification of Tumours Editorial Board. Female Genital Tumours. 5th edition. IARC; 2020.
Leave a Reply