Abnormal villous morphology associated with triple trisomy of paternal origin

Loss of p57 Expression in Conceptions Other Than Complete Hydatidiform Mole: A Case Series With Emphasis on the Etiology, Genetics, and Clinical Significance

Combined p57 immunohistochemistry and DNA genotyping refines classification of products of conception specimens into specific types of hydatidiform moles and various nonmolar entities that can simulate them. p57 expression is highly correlated with genotyping and in practice can reliably be used to identify virtually all complete hydatidiform moles (CHM), but aberrant retained or lost p57 expression in rare CHMs and partial hydatidiform moles (PHM), as well as loss in some nonmolar abortuses, has been reported. Among a series of 2329 products of conceptions, we identified 10 cases for which loss of p57 expression was inconsistent with genotyping results (none purely androgenetic). They displayed a spectrum of generally mild abnormal villous morphology but lacked better developed features of CHMs/early CHMs, although some did suggest subtle forms of the latter. For 5 cases, genotyping (4 cases) and/or ancillary testing (1 case) determined a mechanism for the aberrant p57 results. These included 3 PHMs-2 diandric triploid and 1 triandric tetraploid-and 1 nonmolar specimen with loss of p57 expression attributable to partial or complete loss of the maternal copy of chromosome 11 and 1 nonmolar specimen with Beckwith-Wiedemann syndrome. For 5 cases, including 2 diandric triploid PHMs and 3 biparental nonmolar specimens, genotyping did not identify a mechanism, likely due to other genetic alterations which are below the resolution of or not targeted by genotyping. While overdiagnosis of a PHM as a CHM may cause less harm since appropriate follow-up with serum β-human chorionic gonadotropin levels would take place for both diagnoses, this could cause longer than necessary follow-up due to the expectation of a much greater risk of persistent gestational trophoblastic disease for CHM compared with PHM, which would be unfounded for the correct diagnosis of PHM. Overdiagnosis of a nonmolar abortus with loss of p57 expression as a CHM would lead to unnecessary follow-up and restriction on pregnancy attempts for patients with infertility. Genotyping is valuable for addressing discordance between p57 expression and morphology but cannot elucidate certain mechanisms of lost p57 expression. Future studies are warranted to determine whether chromosomal losses or gains, particularly involving imprinted genes such as p57, might play a role in modifying the risk of persistent gestational trophoblastic disease for PHMs and nonmolar conceptions that are not purely androgenetic but have some abnormal paternal imprinting of the type seen in CHMs.

Genotyping diagnosis of gestational trophoblastic disease: frontiers in precision medicine

Investigations in recent decades have exploited tissue DNA genotyping as a powerful ancillary tool for the precision diagnosis and subclassification of gestational trophoblastic disease. As lesions of gestational origin, the inherited paternal genome, with or without copy number alterations, is the fundamental molecular basis for the diagnostic applications of DNA genotyping. Genotyping is now considered the gold standard in the confirmation and subtyping of sporadic hydatidiform moles. Although a precise diagnosis of partial mole requires DNA genotyping, prognostic stratification according to distinct genetic zygosity in complete moles has recently gained significant clinical relevance for patient care. Beyond hydatidiform moles, DNA genotyping has fundamental applications in the diagnosis or prognostic assessment of gestational trophoblastic tumors, in particular gestational choriocarcinoma. DNA genotyping provides a decisive tool in the separation of gestational trophoblastic neoplasia from non-gestational counterparts/mimics of either germ cell or somatic origin. The FIGO/WHO prognostic scoring scheme requires ascertaining the precise index gestational event and the time interval between the tumor and index gestation, where DNA genotyping can provide highly relevant information. With rapid acquisition of molecular diagnostic capabilities in the clinical practice, DNA genotyping has become closely integrated into the routine diagnostic workup of various forms of gestational trophoblastic disease.

Refined diagnosis of hydatidiform moles with p57 immunohistochemistry and molecular genotyping: updated analysis of a prospective series of 2217 cases

Immunohistochemical analysis of p57 expression and molecular genotyping accurately subclassify molar specimens into complete hydatidiform mole (CHM) and partial hydatidiform mole (PHM) and distinguish these from nonmolar specimens. Characteristics of a prospective series of potentially molar specimens analyzed in a large gynecologic pathology practice are summarized. Of 2217 cases (2160 uterine, 57 ectopic), 2080 (94%) were successfully classified: 571 CHMs (570 uterine, 1 ectopic), 498 PHMs (497 uterine, 1 ectopic), 900 nonmolar (including 147 trisomies, 19 digynic triploids, and 4 donor egg conceptions), and 56 androgenetic/biparental mosaics; 137 were complex or unsatisfactory and not definitively classified. CHMs dominated in patients aged < 21 and >45 years and were the only kind of molar conception found in the latter group. Of 564 successfully immunostained CHMs, 563 (99.8%) were p57-negative (1 p57-positive [retained maternal chromosome 11] androgenetic by genotyping). Of 153 genotyped CHMs, 148 (96.7%) were androgenetic (85% monospermic) and 5 were biparental, the latter likely familial biparental hydatidiform moles. Of 486 successfully immunostained PHMs, 481 (99%) were p57-positive (3 p57-negative [loss of maternal chromosome 11], 2 unknown mechanism). Of 497 genotyped PHMs, 484 (97%) were diandric triploid (99% dispermic) and 13 were triandric tetraploid (all at least dispermic). Of 56 androgenetic/biparental mosaics, 37 had a p57-negative complete molar component (16 confirmed as androgenetic by genotyping). p57 expression is highly correlated with genotyping, serving as a reliable marker for CHMs, and identifies molar components and androgenetic cell lines in mosaic conceptions. Correlation of morphology, p57 expression, genotyping data, and history are required to recognize familial biparental hydatidiform moles and donor egg conceptions, as the former can be misclassified as nonmolar and the latter can be misclassified as dispermic CHM on the basis of isolated genotyping results.

Genetics of gestational trophoblastic disease

The abnormal pregnancies complete and partial hydatidiform mole are genetically unusual, being associated with two copies of the paternal genome. Typical complete hydatidiform moles (CHMs) are diploid and androgenetic, while partial hydatidiform moles (PHMs) are diandric triploids. While diagnosis can usually be made on the basis of morphology, ancillary techniques that exploit their unusual genetic origin can be used to facilitate diagnosis. Genotyping and p57 immunostaining are now routinely used in the differential diagnosis of complete and partial hydatidiform moles, for investigating unusual mosaic or chimeric products of conception with a molar component and identifying the rare diploid, biparental HMs associated with an inherited predisposition to molar pregnancies. Genotyping also plays an important role in the differential diagnosis of gestational and non-gestational trophoblastic tumours and identification of the causative pregnancy where tumours are gestational. Recent developments include the use of cell-free DNA for non-invasive diagnosis of these conditions.

The significance of trisomy 7 mosaicism in noninvasive prenatal screening

Background

This study was an evaluation of the role of noninvasive prenatal testing (NIPT) in the detection of trisomy 7 in prenatal diagnosis.

Method

A total of 35 consecutive cases underwent screening for trisomies by cell-free DNA testing between April 2015 and November 2017 due to suspicious NIPT results; these cases represented 0.11% of patients (35/31,250) with similar frequencies of abnormal results among the laboratories performing the tests. NIPT was offered to further screen for common fetal chromosomal abnormalities. Karyotype analysis, chromosomal microarray analysis (CMA), and next-generation sequencing (NGS) were used to detect 20, 14, and 25 patients, respectively, who accepted confirmatory diagnostic testing.

Results

High-risk results by NIPT were recorded for trisomy 7 alone in 29 women: dual aneuploidy in 4 patients and multiple aneuploidy in 2 patients. Karyotype analysis of amniotic fluid cells was normal in all 20 pregnancies, suggesting a probability of confined placental mosaicism. Further CMA data were obtained in 14 of the cases mentioned above, and 2 fetuses were detected with positive results with copy number variation. The NGS results suggested that all these samples were placental chimerisms of chromosome 7, except for one sample that was found to be an additional chimerism of chromosome 2, which was also consistent with the NIPT result.

Conclusion

Our results may be useful for the counseling of pregnant women in the detection of trisomy 7 by NIPT.

Hydatidiform Moles: Ancillary Techniques to Refine Diagnosis

Context.—

Distinction of hydatidiform moles from nonmolar specimens and subclassification of hydatidiform moles as complete hydatidiform mole versus partial hydatidiform mole are important for clinical practice and investigational studies. Risk of persistent gestational trophoblastic disease and clinical management differ for these entities. Diagnosis based on morphology is subject to interobserver variability and remains problematic, even for experienced gynecologic pathologists.

Objectives.—

To explain how ancillary techniques target the unique genetic features of hydatidiform moles to establish diagnostic truth, highlight the issue of diagnostic reproducibility and importance of diagnostic accuracy, and illustrate use of p57 immunohistochemistry and polymerase chain reaction–based DNA genotyping for diagnosis.

Data Sources.—

Sources are the author's 10-year experience using ancillary techniques for the evaluation of potentially molar specimens in a large gynecologic pathology practice and the literature.

Conclusions.—

The unique genetics of complete hydatidiform moles (purely androgenetic), partial hydatidiform moles (diandric triploid), and nonmolar specimens (biparental, with allelic balance) allow for certain techniques, including immunohistochemical analysis of p57 expression (a paternally imprinted, maternally expressed gene) and genotyping, to refine diagnoses of hydatidiform moles. Although p57 immunostaining alone can identify complete hydatidiform moles, which lack p57 expression because of a lack of maternal DNA, this analysis does not distinguish partial hydatidiform moles from nonmolar specimens because both express p57 because of the presence of maternal DNA. Genotyping, which compares villous and decidual DNA patterns to determine the parental source and ratios of polymorphic alleles, distinguishes purely androgenetic complete hydatidiform moles from diandric triploid partial hydatidiform moles, and both of these from biparental nonmolar specimens. An algorithmic approach to diagnosis using these techniques is advocated.

Abnormal villous morphology mimicking a hydatidiform mole associated with paternal trisomy of chromosomes 3,7,8 and unipaternal disomy of chromosome 11

Background

Pregnancies affected by non-molar chromosomal abnormality may sometimes demonstrate abnormal chorionic villous morphology that is similar to partial hydatidiform mole. Determination of the underlying aetiology may be difficult in such cases.

Case Presentation

This report describes a case referred to the regional trophoblastic disease unit as a possible hydatidiform mole that demonstrated both villous dysmorphology and abnormal p57^KIP2 expression. Molecular genotyping revealed that while most chromosomes in the villous tissue were diploid and biparental, chromosomes 3, 7 and 8 were trisomic with an additional paternally derived chromosome. In contrast chromosome 11 showed uniparental disomy of paternal origin a situation more usually associated with complete hydatidiform moles. This unusual case highlights that exceptions may occur to the general rules of both histological morphology and immunoprofile, and that these can be resolved by detailed molecular genetic investigations.

Conclusion

The findings confirm that trisomic pregnancies may demonstrate morphological villous features similar to hydatidiform mole, and that loss of p57^KIP2 expression occurs due to an absence of maternally transcribed genes on chromosome 11 and can therefore be independent of androgenetic complete hydatidiform mole.

Characteristics of hydatidiform moles: analysis of a prospective series with p57 immunohistochemistry and molecular genotyping

Immunohistochemical analysis of cyclin-dependent kinase inhibitor 1C (CDKN1C, p57, Kip2) expression and molecular genotyping accurately classify hydatidiform moles into complete and partial types and distinguish these from non-molar specimens. Characteristics of a prospective series of all potentially molar specimens encountered in a large gynecologic pathology practice are summarized. Initially, all specimens were subjected to both analyses; this was later modified to triage cases for genotyping based on p57 results: p57-negative cases diagnosed as complete hydatidiform moles without genotyping; all p57-positive cases genotyped. Of the 678 cases, 645 were definitively classified as complete hydatidiform mole (201), partial hydatidiform mole (158), non-molar (272), and androgenetic/biparental mosaic (14); 33 were unsatisfactory, complex, or problematic. Of the 201 complete hydatidiform moles, 104 were p57-negative androgenetic and an additional 95 were p57-negative (no genotyping), 1 was p57-positive (retained maternal chromosome 11) androgenetic, and 1 was p57-non-reactive androgenetic; 90 (85%) of the 106 genotyped complete hydatidiform moles were monospermic and 16 were dispermic. Of the 158 partial hydatidiform moles, 155 were diandric triploid, with 154 p57-positive, 1 p57-negative (loss of maternal chromosome 11), and 1 p57-non-reactive; 3 were triandric tetraploid, with 2 p57-positive and 1 p57-negative (loss of maternal chromosome 11). Of 155 diandric triploid partial hydatidiform moles, 153 (99%) were dispermic and 2 were monospermic. Of the 272 non-molar specimens, 259 were p57-positive biparental diploid, 5 were p57-positive digynic triploid, 2 were p57-negative biparental diploid (no morphological features of biparental hydatidiform mole), and 6 were p57-non-reactive biparental diploid. Of the 14 androgenetic/biparental mosaics with discordant p57 expression, 6 were uniformly mosaic and 8 had a p57-negative androgenetic molar component. p57 expression is highly correlated with genotyping, serves as a reliable marker for diagnosis of complete hydatidiform moles, and identifies androgenetic cell lines in mosaic conceptions. Cases with aberrant and discordant p57 expression can be correctly classified by genotyping.

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.

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.

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.