Diagnosis and Subclassification of Hydatidiform Moles Using p57 Immunohistochemistry and Molecular Genotyping: Validation and Prospective Analysis in Routine and Consultation Practice Settings With Development of an Algorithmic Approach

Partial hydatidiform mole: histologic parameters in correlation with DNA genotyping

Histologic diagnosis of partial hydatidiform mole (PHM) continues to be problematic, and DNA genotyping has recently become cost-effective for precise separation of PHM from its mimics. We performed a comprehensive reevaluation of histologic parameters of PHM in correlation with DNA genotyping. A total of 143 early abortion specimens were subjected to genotyping as part of the routine workup, resulting in 60 cases of PHM, 52 cases of various chromosomal trisomies, and 31 cases of nonmolar diploid gestations. All available hematoxylin and eosin slides were reviewed retrospectively by 2 gynecologic pathologists blinded to the genotyping results. Significant histologic overlaps were present among genetically confirmed PHM, hydropic abortions, and chromosomal trisomy syndromes. The following morphologic parameters emerged with diagnostic significance for PHM: villus size, presence of 2 villous populations, round or oval pseudoinclusions, at least moderate villous hydrops, cistern formation, and trophoblastic hyperplasia. The most sensitive morphologic features for PHM included villous hydrops (86% sensitivity) or the presence of at least 1 of the following 3 parameters: 2 villous populations, round or oval pseudoinclusions, and cisterns (84% sensitivity). The presence of cisterns and villous size ≥2.5 mm had the highest positive predictive value (90%) for PHM. In conclusion, no single or combined morphologic features are sufficient for definitive diagnosis of PHM. The presence of any one of the following histologic findings should prompt DNA genotyping workup to rule out PHM: round or oval pseudoincludions, cistern formation, 2 populations of villi, and a villous size of ≥2.5 mm.

Characterization of androgenetic/biparental mosaic/chimeric conceptions, including those with a molar component: morphology, p57 immnohistochemistry, molecular genotyping, and risk of persistent gestational trophoblastic disease

Recent studies have demonstrated the value of ancillary techniques, including p57 immunohistochemistry and short tandem repeat genotyping, for distinguishing hydatidiform moles (HM) from nonmolar specimens and for subtyping HMs as complete hydatidiform moles (CHM) and partial hydatidiform moles (PHM). With rare exceptions, CHMs are p57-negative and androgenetic diploid; partial hydatidiform moles are p57-positive and diandric triploid; and nonmolar specimens are p57-positive and biparental diploid. Androgenetic/biparental mosaic/chimeric conceptions can have morphologic features that overlap with HMs but are genetically distinct. This study characterizes 11 androgenetic/biparental mosaic/chimeric conceptions identified in a series of 473 products of conception specimens subjected to p57 immunohistochemistry and short tandem repeat genotyping. Fluorescence in situ hybridization was performed on 10 to assess ploidy. All cases were characterized by hydropically enlarged, variably sized and shaped villi. In 5 cases, the villi lacked trophoblastic hyperplasia, whereas in 6 there was a focal to extensive villous component with trophoblastic hyperplasia and features of CHM. The villi lacking trophoblastic hyperplasia were characterized by discordant p57 expression within individual villi (p57-positive cytotrophoblast and p57-negative stromal cells), whereas the villous components having trophoblastic hyperplasia were uniformly p57-negative in both cell types. Short tandem repeat genotyping of at least 2 villous areas in each case demonstrated an excess of paternal alleles in all regions, with variable paternal:maternal allele ratios (usually >2:1); pure androgenetic diploidy was identified in those cases with a sufficiently sized villous component having trophoblastic hyperplasia and features of CHM. Fluorescence in situ hybridization demonstrated uniform diploidy in 7 cases, including 4 of 5 tested cases with trophoblastic hyperplasia and 3 of 5 cases without trophoblastic hyperplasia. Two cases without trophoblastic hyperplasia had uniformly diploid villous stromal cells but 1 had triploid and 1 had tetraploid cytotrophoblast; 1 case with trophoblastic hyperplasia had uniformly diploid villous stromal cells but a mixture of diploid, triploid, and tetraploid cytotrophoblast. In 3 cases with a CHM component, persistent gestational trophoblastic disease developed. These results indicate that androgenetic/biparental mosaic/chimeric conceptions are most often an admixture of androgenetic diploid (p57-negative) and biparental diploid (p57-positive) cell lines but some have localized hyperdiploid components. Recognition of their distinctive p57 expression patterns and genotyping results can prevent misclassification as typical CHMs, PHMs, or nonmolar specimens. The presence of androgenetic cell lines, particularly in those with a purely androgenetic CHM component, warrants follow-up because of some risk of persistent gestational trophoblastic disease.

Placental Mesenchymal Dysplasia

Placental mesenchymal dysplasia is a rare, incompletely understood placental stromal lesion, characterized by placentomegaly and striking ectasia and tortuosity of chorionic plate and stem villous vessels. Its prenatal ultrasonographic and gross pathologic features resemble those of a partial mole, but the fetus is typically normal and the placenta has a diploid, chromosomal complement. We discuss the pathologic features and current understanding of the etiopathogenesis of this condition, the supportive immunohistochemical and confirmatory molecular genetic studies important in its diagnosis, and its implications for pregnancy and infant outcomes.

Diagnostic utility of microsatellite genotyping for molar pregnancy testing

CONTEXT

Molecular genotyping by analysis of DNA microsatellites, also known as short tandem repeats (STRs), is an established method for diagnosing and classifying hydatidiform mole. Distinction of both complete hydatidiform mole and partial hydatidiform mole from nonmolar specimens is relevant for clinical management owing to differences in risk for persistent gestational trophoblastic disease.

OBJECTIVE

To determine the technical performance of microsatellite genotyping by using a commercially available multiplex assay, and to describe the application of additional methods to confirm other genetic abnormalities detected by the genotyping assay.

DESIGN

Microsatellite genotyping data on 102 cases referred for molar pregnancy testing are presented. A separate panel of mini STR markers, flow cytometry, fluorescence in situ hybridization, and p57 immunohistochemistry were used to characterize cases with other incidental genetic abnormalities.

RESULTS

Forty-eight cases were classified as hydatidiform mole (31, complete hydatidiform mole; 17, partial hydatidiform mole). Genotyping also revealed 11 cases of suspected trisomy and 1 case of androgenetic/biparental mosaicism. Trisomy for selected chromosomes (13, 16, 18, and 21) was confirmed in all cases by using a panel of mini STR markers.

CONCLUSIONS

This series illustrates the utility of microsatellite genotyping as a stand-alone method for accurate classification of hydatidiform mole. Other genetic abnormalities may be detected by genotyping; confirmation of the suspected abnormality requires additional testing.

Diagnostic reproducibility of hydatidiform moles: ancillary techniques (p57 immunohistochemistry and molecular genotyping) improve morphologic diagnosis for both recently trained and experienced gynecologic pathologists

Distinction of hydatidiform moles from nonmolar specimens (NMs) and subclassification of hydatidiform moles as complete hydatidiform mole (CHM) and partial hydatidiform mole (PHM) are important for clinical practice and investigational studies; however, diagnosis based solely on morphology is affected by interobserver variability. Molecular genotyping can distinguish these entities by discerning androgenetic diploidy, diandric triploidy, and biparental diploidy to diagnose CHMs, PHMs, and NMs, respectively. Eighty genotyped cases (27 CHMs, 27 PHMs, 26 NMs) were selected from a series of 200 potentially molar specimens previously diagnosed using p57 immunohistochemistry and genotyping. Cases were classified by 6 pathologists (3 faculty level gynecologic pathologists and 3 fellows) on the basis of morphology, masked to p57 immunostaining and genotyping results, into 1 of 3 categories (CHM, PHM, or NM) during 2 diagnostic rounds; a third round incorporating p57 immunostaining results was also conducted. Consensus diagnoses (those rendered by 2 of 3 pathologists in each group) were also determined. Performance of experienced gynecologic pathologists versus fellow pathologists was compared, using genotyping results as the gold standard. Correct classification of CHMs ranged from 59% to 100%; there were no statistically significant differences in performance of faculty versus fellows in any round (P-values of 0.13, 0.67, and 0.54 for rounds 1 to 3, respectively). Correct classification of PHMs ranged from 26% to 93%, with statistically significantly better performance of faculty versus fellows in each round (P-values of 0.04, <0.01, and <0.01 for rounds 1 to 3, respectively). Correct classification of NMs ranged from 31% to 92%, with statistically significantly better performance of faculty only in round 2 (P-values of 1.0, <0.01, and 0.61 for rounds 1 to 3, respectively). Correct classification of all cases combined ranged from 51% to 75% by morphology and 70% to 80% with p57, with statistically significantly better performance of faculty only in round 2 (P-values of 0.69, <0.01, and 0.15 for rounds 1 to 3, respectively). p57 immunostaining significantly improved recognition of CHMs (P<0.01) and had high reproducibility (κ=0.93 to 0.96) but had no impact on distinction of PHMs and NMs. Genotyping provides a definitive diagnosis for the ∼25% to 50% of cases that are misclassified by morphology, especially those that are also unresolved by p57 immunostaining.

Siglec-6 is expressed in gestational trophoblastic disease and affects proliferation, apoptosis and invasion

Sialic acid immunoglobulin-like lectin (Siglec)-6 is a transmembrane receptor that binds leptin. Leptin is an obesity-associated peptide hormone overexpressed in gestational trophoblastic disease (GTD). GTD encompasses several placental abnormalities that range from benign to malignant. Among GTD, molar placentas are characterized by excess proliferation, whereas gestational trophoblastic neoplasias (GTN) have characteristically aggressive invasion. We hypothesized that in GTD, Siglec-6 expression would increase with disease severity and that Siglec-6 and leptin would promote proliferation, inhibit apoptosis and/or promote invasion. Siglec-6 expression patterns were evaluated with particular attention to the diagnostic utility of Siglec-6 in GTD (controls: normal placentas (n=32), hydropic abortus placentas (n=7), non-GTD reproductive tract cancers (n=2); GTD: partial moles (PM; n=11), complete moles (n=24), GTN (n=6)). In normal placentas, Siglec-6 expression dramatically decreased after 8 weeks gestation. Complete molar placentas had significantly higher Siglec-6 expression than controls, but expression was not significantly different from PM. In GTN, Siglec-6 expression was low. These data suggest that Siglec-6 may have diagnostic utility for distinguishing complete moles from normal and hydropic abortus placentas. Functional studies in choriocarcinoma-derived BeWO cells demonstrated a complex interplay between Siglec-6 expression and leptin exposure. In cells lacking Siglec-6, leptin treatment promoted invasion, likely through interaction with LepR leptin receptor, without affecting proliferation or apoptosis. Siglec-6 expression promoted proliferation in a leptin-dependent manner, but protected cells from apoptosis and promoted invasion in a leptin-independent manner. We propose that Siglec-6 and leptin play a role in the aberrant properties characteristic of GTD, namely excess proliferation and invasion.

Diagnostic reproducibility of hydatidiform moles: ancillary techniques (p57 immunohistochemistry and molecular genotyping) improve morphologic diagnosis

Distinction of hydatidiform moles (HMs) from nonmolar specimens (NMs) and subclassification of HMs as complete hydatidiform moles (CHMs) and partial hydatidiform moles (PHMs) are important for clinical practice and investigational studies; yet, diagnosis based solely on morphology is affected by interobserver variability. Molecular genotyping can distinguish these entities by discerning androgenetic diploidy, diandric triploidy, and biparental diploidy to diagnose CHMs, PHMs, and NMs, respectively. Eighty genotyped cases (27 CHMs, 27 PHMs, and 26 NMs) were selected from a series of 200 potentially molar specimens previously diagnosed using p57 immunostaining and genotyping. Cases were classified by 3 gynecologic pathologists on the basis of H&E slides (masked to p57 immunostaining and genotyping results) into 1 of 3 categories (CHM, PHM, or NM) during 2 diagnostic rounds; a third round incorporating p57 immunostaining results was also conducted. Consensus diagnoses (those rendered by 2 of 3 pathologists) were determined. Genotyping results were used as the gold standard for assessing diagnostic performance. Sensitivity of a diagnosis of CHM ranged from 59% to 100% for individual pathologists and from 70% to 81% by consensus; specificity ranged from 91% to 96% for individuals and from 94% to 98% by consensus. Sensitivity of a diagnosis of PHM ranged from 56% to 93% for individual pathologists and from 70% to 78% by consensus; specificity ranged from 58% to 92% for individuals and from 74% to 85% by consensus. The percentage of correct classification of all cases by morphology ranged from 55% to 75% for individual pathologists and from 70% to 75% by consensus. The κ values for interobserver agreement ranged from 0.59 to 0.73 (moderate to good) for a diagnosis of CHM, from 0.15 to 0.43 (poor to moderate) for PHM, and from 0.13 to 0.42 (poor to moderate) for NM. The κ values for intraobserver agreement ranged from 0.44 to 0.67 (moderate to good). Addition of the p57 immunostain improved sensitivity of a diagnosis of CHM to a range of 93% to 96% for individual pathologists and 96% by consensus; specificity was improved from a range of 96% to 98% for individual pathologists and 96% by consensus; there was no substantial impact on diagnosis of PHMs and NMs. Interobserver agreement for interpretation of the p57 immunostain was 0.96 (almost perfect). Even with morphologic assessment by gynecologic pathologists and p57 immunohistochemistry, 20% to 30% of cases will be misclassified, and, in particular, distinction of PHMs and NMs will remain problematic.

Diandric triploid hydatidiform mole with loss of maternal chromosome 11

Distinction of hydatidiform moles (HM) from nonmolar specimens and their subclassification as complete (CHM) versus partial hydatidiform mole (PHM) are important for clinical practice and investigational studies to refine ascertainment of risk of persistent gestational trophoblastic disease (GTD), which differs among these entities. Immunohistochemical analysis of p57 expression, a paternally imprinted maternally expressed gene on 11p15.5, and molecular genotyping are useful for improving diagnosis. CHMs are characterized by androgenetic diploidy, with loss of p57 expression due to lack of maternal DNA. Loss of p57 expression distinguishes CHMs from both PHMs (diandric triploidy) and nonmolar specimens (biparental diploidy), which retain expression. We report a unique HM characterized by morphologic features suggesting an early CHM, including lack of p57 expression by immunohistochemistry, but with genetic features more in keeping with a PHM. Specifically, molecular genotyping by short tandem repeat markers provided evidence to support interpretation as a PHM by demonstrating allele patterns and ratios most consistent with diandric triploidy, with evidence of loss of the maternal copy of chromosome 11 to explain the lack of p57 expression. This case illustrates the value of combined traditional pathologic and ancillary molecular techniques for refined diagnosis of molar specimens. It also raises questions regarding which modalities should be used to ultimately define the subtypes of HMs and whether chromosomal losses or gains, particularly involving imprinted genes such as p57, might play a role in modifying risk of persistent GTD.

Molecular diagnosis of gestational trophoblastic disease

Gestational trophoblastic disease consists of well-defined diagnostic entities of proliferative disorder of the placenta, of which hydatidiform moles are common lesions. Even with available ancillary studies, including ploidy and immunohistochemistry analyses, histological diagnosis of molar pregnancies can be challenging in a significant percentage of the cases. Reliable diagnostic approaches with improved sensitivity and specificity are highly desirable. Recently, PCR-based short tandem repeat DNA genotyping has emerged as a powerful diagnostic measure in the workup of gestational trophoblastic disorders, particularly hydatidiform moles.

Diagnosis of hydatidiform moles by polymorphic deletion probe fluorescence in situ hybridization

Because products of conception often contain maternal and villous tissues, the determination of maternal and villous genotypes based on genetic polymorphisms can help discern maternal and paternal chromosomal contribution and aid in the diagnosis of hydatidiform moles. Polymorphic deletion probe (PDP) fluorescence in situ hybridization (FISH) probes based on copy number variants are highly polymorphic and allow in situ determination of genetic identity. By using three informative PDPs on chromosomes 2p, 4q, and 8p, we compared maternal with villous genotypes and determined the ploidy of villous tissue. PDP FISH was performed on 13 complete moles, 13 partial moles, 13 nonmolar abortions, and an equivocal hydropic abortion. PDP FISH permitted definitive diagnosis of complete moles in five of 13 cases for which maternal and villous genotypes were mutually exclusive. A complete mole was highly suspected when all three PDP loci showed homozygous villous genotypes. The diagnosis of a complete mole by PDP FISH yielded a theoretical test sensitivity of 87.5%, specificity of 91.8%, an observed test sensitivity of 100%, and specificity of 92.3%. Triploidy was observed in all partial moles, in which diandric triploidy was confirmed in six cases. In the equivocal hydropic abortion, PDP FISH combined with p57 immunofluorescence revealed placental androgenetic/biparental mosaicism. PDP FISH can be used in clinical practice and research studies to subclassify hydatidiform moles and evaluate unusual products of conception.

Precise DNA genotyping diagnosis of hydatidiform mole

OBJECTIVE

To estimate whether tissue DNA genotyping is effective for the confirmation and subclassification of hydatidiform moles.

METHODS

Consecutive cases of products of conception were selected based on histologic alterations that are suspicious for molar pregnancy. DNA genotyping was performed by a multiplex polymerase chain reaction targeting 15 tetrameric polymorphic loci of the human genome.

RESULTS

A total of 205 products of conception were included. DNA genotyping was informative in all, leading to the final identification of 60 cases of hydatidiform moles, including 17 complete and 43 partial moles. Among 17 cases of complete moles, 14 cases were monospermic and three were dispermic. Forty-three cases were confirmed as triploid partial moles, 42 of which were dispermic and one was monospermic. Among nonmolar cases, 32 gestations showed allelic changes indicating chromosomal alterations, including 28 cases of trisomy syndrome: trisomy 16 (eight cases), trisomy 21 (six cases), trisomy 7 (three cases), trisomy 13 (three cases), trisomy 4 (one case), trisomy 8 (one case), trisomy 18 (one case), XXY/Klinefelter syndrome (one case), and multiple trisomies (four cases). Monosomy 22 was seen in one case. Two nonmolar cases were triploid digynic-monoandric gestations. More complex chromosomal abnormalities were seen in one case. The remaining 113 cases were balanced biallelic gestations.

CONCLUSION

Tissue DNA genotyping is a practical and highly accurate method for the confirmation and subclassification of hydatidiform moles.

LEVEL OF EVIDENCE

III.

Abnormal villous morphology associated with triple trisomy of paternal origin

The vast majority of trisomies in spontaneous abortions (SAB) are single and of maternal origin, most frequently due to meiosis I errors. Triple trisomies are exceedingly rare (approximately 0.05% of spontaneous abortions), most often of maternal origin, and associated with increased maternal age. Some trisomic SAB specimens can exhibit abnormal villous morphology simulating a partial hydatidiform mole, a distinct form of hydatidiform mole characterized by diandric triploidy. A SAB specimen from a 27-year-old woman, G1P0 at 8 weeks gestational age, was reviewed in consultation to address the finding of morphological features suggestive of a partial hydatidiform mole but DNA ploidy analysis yielding a diploid result. The villi were irregularly shaped and hydropic but lacked trophoblastic hyperplasia; p57 expression was retained. Since fully developed features of a partial hydatidiform mole were lacking, additional analysis was performed. Molecular genotyping and single nucleotide polymorphism array analysis demonstrated biparental diploidy with trisomy of chromosomes 7, 13, and 20, all of paternal origin. The three trisomies may have originated from paternal meiosis II errors, or from mitotic nondisjunction. We believe this to be the first report of triple trisomy in a SAB confirmed to be of paternal origin.

Comparison of fluorescence in situ hybridization, p57 immunostaining, flow cytometry, and digital image analysis for diagnosing molar and nonmolar products of conception

Pathologic examination of products of conception (POC) is used to differentiate hydropic abortus (HA), partial hydatidiform mole (PM), and complete hydatidiform mole (CM). Histologic classification of POC specimens can be difficult, and ancillary testing is often required for a definitive diagnosis. This study evaluated 66 POC specimens by flow cytometry, digital image analysis, p57 immunohistochemical analysis, and fluorescence in situ hybridization (FISH). The final diagnosis, based on the combined analysis of all test results, included 33 HAs, 24 PMs, and 9 CMs. The p57 immunostain identified 9 CMs that were evaluated as nontriploid by all other techniques. FISH seems to have the best accuracy (100%) for determining whether a specimen contains a triploid chromosome complement. These data suggest that the combination of p57 and FISH seems to be the best ancillary testing strategy to aid pathologists in the appropriate identification of CM, PM, and HA in POC specimens.

Molecular genotyping of hydatidiform moles: analytic validation of a multiplex short tandem repeat assay

Distinction of hydatidiform moles from non-molar (NM) specimens, as well as their subclassification as complete (CHM) versus partial hydatidiform moles (PHM), is important for clinical management and accurate risk assessment for persistent gestational trophoblastic disease. Because diagnosis of hydatidiform moles based solely on morphology suffers from poor interobserver reproducibility, a variety of ancillary techniques have been developed to improve diagnosis. Immunohistochemical assessment of the paternally imprinted, maternally expressed p57 gene can identify CHMs (androgenetic diploidy) by their lack of p57 expression, but cannot distinguish PHMs (diandric monogynic triploidy) from NMs (biparental diploidy). Short tandem repeat genotyping can identify the parental source of polymorphic alleles and thus discern androgenetic diploidy, diandric triploidy, and biparental diploidy, which allows for specific diagnosis of CHMs, PHMs, and NMs, respectively. In this study, a retrospectively collected set of morphologically typical CHMs (n = 8), PHMs (n = 10), and NMs (n = 12) was subjected to an analytic validation study of both short tandem repeat genotyping and p57 immunohistochemistry. Several technical and biological problems resulted in data that were difficult to interpret. To avoid these pitfalls, we have developed an algorithm with quantitative guidelines for the interpretation of short tandem repeat genotyping data.