Flow cytometric and clinicopathologic study of complete hydatidiform moles with special reference to the significance of cytometric aneuploidy

Complementary role of p57kip2 immunostaining in diagnosing hydatidiform mole subtypes

OBJECTIVES

Gestational trophoblastic disease comprises of a spectrum of pregnancy-related tumours which includes complete (CHM) and partial hydatidiform moles (PHM). Accurate diagnosis and subclassification of HM subtypes are crucial as prognosis differs. Histopathological examination using haemotoxylin and eosin (H&E) staining remains the basis for diagnosing HM, with only 80% accuracy. p57kip2 is a cyclin-dependent kinase inhibitor (CDKI) protein and is strongly paternally imprinted, being expressed from maternal allele. Therefore, complete mole (CHM) with only paternal genome has nearly absent expression of p57kip2 compared to partial mole (PHM) having both paternal and maternal genomes. This study is aimed to determine usefulness of p57kip2 immunohistochemistry (IHC) analysis in the diagnosis of HM subtypes.

METHODS

A total of 82 archived paraffin embedded HM tissues with subtypes classified based on H&E staining - 39 (47.5%) CHM, 41 (50.0%) PHM and two (2.43%) unclassified molar pregnancy were retrieved. All tissue samples were subjected for p57kip2 IHC analysis and HM subtypes were then reclassified.

RESULTS

A total of 66 cases (80.5%) were re-classified as CHM, 14 cases (17.1%) as PHM and two cases (2.4%) were decidual and cystic tissues. Analysis using p57kip2 immunostaining showed a diagnostic discrepancy of 33.0% from routine H&E staining and helps to improve the characterisation of the HM subtypes specifically at early gestations which have less distinctive morphologies.

CONCLUSIONS

IHC using p57kip2 monoclonal antibody should be considered as a routine ancillary test to H&E in improving the diagnosis of HM subtypes particularly in developing countries with limited resources.

Expression of p57KIP2 reduces growth and invasion, and induces syncytialization in a human placental choriocarcinoma cell line, BeWo

INTRODUCTION

Syncytiotrophoblasts are the major components of the human placenta involved in fetal maternal exchange and hormone secretion. The syncytiotrophoblasts arise from the fusion of villous cytotrophoblasts. The cell cycle suppressor p57^KIP2 is known to be an essential molecule for proper trophoblast differentiation during placental formation.

METHODS

We generated p57^KIP2-expressing BeWo transfectant cells. Proliferation assay and matrigel invasion assay were used to characterize p57^KIP2-expressing BeWo transfectant cells. To reveal the role of p57^KIP2 in syncytialization, we proceeded syncytium formation analysis and qRT-PCR for detection of the expression levels Syncytin-1, Syncytin-2 and their receptors.

RESULTS

The human choriocarcinoma cell line, BeWo has undetectable levels of p57^KIP2 expression. Expression of p57^KIP2 reduced cell proliferation rate and extracellular matrix invasion activity. p57^KIP2 expressing cells displayed multinucleated cells associated with syncytiotrophoblast differentiation. In the syncytialization event, p57^KIP2 was found to potentiate forskolin-induced upregulation of Syncytin-2 in a cAMP-independent manner.

DISCUSSION

These results indicate that the expression of p57^KIP2 may act on the proliferation/invasion inhibitory factor and enhance the expression of Syncytin-2, which are associated with syncytialization in cytotrophoblasts.

Loss of p57KIP2 expression confers resistance to contact inhibition in human androgenetic trophoblast stem cells

Complete hydatidiform moles (CHMs) develop from androgenetic conceptuses and are characterized by enhanced proliferation of trophoblast cells and a significantly higher risk of trophoblast tumors. Loss of the maternal genome and duplication of the paternal genome are considered to be responsible for the phenotype, but the detailed mechanism remains unclear. Here, we report the derivation of trophoblast stem (TS) cells from CHMs. These cells have reduced sensitivity to contact inhibition of cell proliferation and exhibit aberrant expression of imprinted genes, which are expressed from only 1 parental allele. We also reveal that the maternally expressed imprinted gene p57^KIP2 would be responsible for the enhanced proliferation of CHM-derived TS cells. Our findings provide an insight into the pathogenesis of CHMs.

A complete hydatidiform mole (CHM) is androgenetic in origin and characterized by enhanced trophoblastic proliferation and the absence of fetal tissue. In 15 to 20% of cases, CHMs are followed by malignant gestational trophoblastic neoplasms including choriocarcinoma. Aberrant genomic imprinting may be responsible for trophoblast hypertrophy in CHMs, but the detailed mechanisms are still elusive, partly due to the lack of suitable animal or in vitro models. We recently developed a culture system of human trophoblast stem (TS) cells. In this study, we apply this system to CHMs for a better understanding of their molecular pathology. CHM-derived TS cells, designated as TS^mole cells, are morphologically similar to biparental TS (TS^bip) cells and express TS-specific markers such as GATA3, KRT7, and TFAP2C. Interestingly, TS^mole cells have a growth advantage over TS^bip cells only after they reach confluence. We found that p57^KIP2, a maternally expressed gene encoding a cyclin-dependent kinase inhibitor, is strongly induced by increased cell density in TS^bip cells, but not in TS^mole cells. Knockout and overexpression studies suggest that loss of p57^KIP2 expression would be the major cause of the reduced sensitivity to contact inhibition in CHMs. Our findings shed light on the molecular mechanism underlying the pathogenesis of CHMs and could have broad implications in tumorigenesis beyond CHMs because silencing of p57^KIP2 is frequently observed in a variety of human tumors.

Identity determination in diagnostic surgical pathology

From a technical perspective, specimen identity determination in surgical pathology over the last several decades has primarily focused on analysis of repetitive DNA sequences, specifically microsatellite repeats. However, a number of techniques have recently been developed that have similar, if not greater, utility in surgical pathology, most notably analysis of single nucleotide polymorphism (SNPs) and gene panels by next generation sequencing (NGS). For cases with an extremely limited sample or a degraded sample, sequence analysis of mitochondrial DNA continues to be the method of choice. From a diagnostic perspective, interest in identity determination in surgical pathology is usually centered on resolving issues of specimen provenance due to specimen labeling/accessioning deficiencies and possible contamination, but is also frequently performed in cases for which the patient's clinical course following definitive therapy is remarkably atypical, in cases of an unexpected diagnosis, and by patient request for "peace of mind". However, the methods used for identity determination have a much broader range of applications in surgical pathology beyond tissue provenance analysis. The methods can be used to provide ancillary information for cases in which the histomorphology is not definitively diagnostic, as for example for tumors that have a virtually identical microscopic appearance but for which the differential diagnosis includes synchronous/metachronous tumors versus a metastasis, and for the diagnosis of hydropic early gestations versus hydatidiform molar pregnancies. The methods also have utility in several other clinical settings, for example to rule out a donor-transmitted malignancy in a transplant recipient, to monitor bone marrow transplant engraftment, and to evaluate natural chimerism.

Flow Cytometric DNA Analysis and Histopathologic Re-Evaluation of Paraffin Embedded Samples from Hydatidiform Moles and Hydropic Abortions

Background

Distinction of hydatidiform moles (HMs) from non-molar abortions and sub-classification of HMs are important for clinical practice; yet, diagnosis based solely on morphology is affected by interobserver variability. The objective of this study was to determine the role of DNA flow cytometry in distinguishing molar from non-molar pregnancies.

Materials and Methods

This retrospective study was conducted at the Department of Pathology, Women’s Hospital, Tehran University of Medical Sciences, Tehran, Iran, between 2006 and 2010. DNA ploidy analysis and histopathologic re-evaluation were performed on paraffin-embedded tissue from 36 (17 complete and 19 partial) molar and 24 hydropic abortus (HA) cases which were previously diagnosed based on histomorphologic study.

Results

Of the 17 cases initially diagnosed as complete HM (CHM), 9 were diploid, 2 were triploid, 5 were tetraploid and 1 was aneuploid. Of the 19 initial partial HMs (PHMs), 2, 8, 1 and 8 cases were diploid, triploid, tetraploid and aneuploid, respectively. In the initial HA category (n=24), 14 diploid, 1 triploid, 5 tetraploid, and 4 aneuploid cases existed. Following flow cytometry and histopathologic reevaluation, 1 case with previous diagnosis of HA was reclassified as PHM, 2 initial PHMs were reclassified as CHM and 2 initial CHMs were categorized as PHM.

Conclusion

The results show that correct diagnosis of PMH is the main challenge in histological diagnosis of gestational trophoblastic disease (GTD). DNA flow cytometric analysis could be an informative supplement to the histological interpretation of molar and hydropic placentas.

[Twin pregnancy with complete mole and coexisting fetus: Reach fetal viability is possible]

Twin pregnancies combining complete hydatidiform mole and coexistent fetus are a rare situation (incidence in 1/20,000 in 1/100,000 pregnancies) and a challenge for diagnosis. Their complications can be important - bleeding, preeclampsia, miscarriage - and their management remains complex and controversial. In case of continuing the pregnancy, nearly 40% of women have lives babies. Three quarters of fetal loss occur before 24weeks gestation. We report here three new cases; only one of these cases had a favorable outcome.

A metal-containing nucleoside that possesses both therapeutic and diagnostic activity against cancer

Nucleoside transport is an essential process that helps maintain the hyperproliferative state of most cancer cells. As such, it represents an important target for developing diagnostic and therapeutic agents that can effectively detect and treat cancer, respectively. This report describes the development of a metal-containing nucleoside designated Ir(III)-PPY nucleoside that displays both therapeutic and diagnostic properties against the human epidermal carcinoma cell line KB3-1. The cytotoxic effects of Ir(III)-PPY nucleoside are both time- and dose-dependent. Flow cytometry analyses validate that the nucleoside analog causes apoptosis by blocking cell cycle progression at G2/M. Fluorescent microscopy studies show rapid accumulation in the cytoplasm within 4 h. However, more significant accumulation is observed in the nucleus and mitochondria after 24 h. This localization is consistent with the ability of the metal-containing nucleoside to influence cell cycle progression at G2/M. Mitochondrial depletion is also observed after longer incubations (Δt ∼48 h), and this effect may produce additional cytotoxic effects. siRNA knockdown experiments demonstrate that the nucleoside transporter, hENT1, plays a key role in the cellular entry of Ir(III)-PPY nucleoside. Collectively, these data provide evidence for the development of a metal-containing nucleoside that functions as a combined therapeutic and diagnostic agent against cancer.

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.

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.

NLRP7 mutations in women with diploid androgenetic and triploid moles: a proposed mechanism for mole formation

Hydatidiform mole is an aberrant pregnancy with abnormal embryonic development and hydropic placental villi. Common moles are sporadic, not recurrent and affect one in every 1500 pregnancies in Western societies. Approximately, half of common moles are complete and mostly diploid androgenetic, whereas the remaining are partial and mostly triploid diandric. NLRP7 has been found to be responsible for a recurrent form of molar pregnancies. Recently, we showed that patients with NLRP7 mutations have an impaired inflammatory response to various stimuli. To date, molar tissues analyzed from patients with NLRP7 mutations have been found to be diploid and biparental. In this study, we report 10 new non-synonymous variants and one stop codon found in patients and not in controls. We demonstrate the presence of different types of moles, diploid biparental, diploid androgenetic, triploid and tetraploid conceptions, in patients with NLRP7 variants. We document in vitro and in vivo early embryo cleavage abnormalities in three patients. We propose a two-hit mechanism at the origin of androgenetic moles. This mechanism consists of variable degrees of early embryo cleavage abnormalities leading to chaotic mosaic aneuploidies, with haploid, diploid, triploid and tetraploid blastomeres. Surviving embryonic cells that reach implantation are then subject to the maternal immune response. Because of the patients' impaired inflammatory response, androgenetic cells, which are complete allograft, are able to grow and proliferate. In women with normal immune system, chaotic mosaic aneuploidies may also occur during early cleavage, however, androgenetic cells would die after implantation or stay undetected, confined to a small portion of the placenta.

A distinct pattern in the DNA ploidy histograms of hydatidiform moles and nonmolar abortuses is caused by accumulation of trophoblasts in the late s-phase

DNA ploidy analysis is a useful tool to distinguish the partial hydatidiform moles (PMs) from complete hydatidiform moles (CMs) and nonmolar abortuses (NAs). DNA ploidy histograms of hydatidiform moles are sometimes difficult to interpret because of the uneven distribution of nuclei in the S-phase, simulating aneuploid peaks. In this study, we analyzed DNA ploidy histograms of 25 CMs, 16 PMs, and 28 NAs, with special reference to the accumulation of cells in the late S-phase using a high-resolution DNA image cytometry. All the gestational products demonstrated the accumulation of cells in the late part of the S-phase fraction. To objectify the observation, we compared the percentage of cells in the second quarter with that of the third quarter of the S-phase fraction. All the gestational products had significantly lower (P < 0.001) percentage of cells in the second compared with that of the third quarter of the S-phase. The mean ratios of the third quarter to the second quarter in CMs, PMs, and NAs were 1.9, 1.7, and 2.5, respectively. This was significantly different from that of highly proliferative endometrial carcinomas. The knowledge of this specific S-phase fraction distribution in molar and nonmolar pregnancy material is important when interpreting the DNA histograms. The possibility of hypoxia being the cause of this phenomenon is also discussed.

Detection of non-maternal components of gestational choriocarcinoma by PCR-based microsatellite DNA assay

OBJECTIVE

Gestational and non-gestational choriocarcinomas have distinctly different tissues of origin, parental genotypes, natural histories, and responses to therapy. Our objective was to develop a convenient, fast, and reliable assay that would, using only patient tissue, allow separation of gestational from non-gestational choriocarcinomas.

METHOD

Benign and malignant tissues, preserved in paraffin blocks and separated by microdissection, were examined using a commercial PCR-based tissue identity assay (ABI AmpFlSTR Profiler Plus Kit and ABI 377 DNA sequencer) to detect genetic profiles of 9 microsatellite markers, along with X and Y chromosome markers. Cases included 6 choriocarcinomas. Controls included eight non-germ cell reproductive tract tumors and two hydatidiform moles.

RESULTS

The microsatellite markers identified the five choriocarcinomas diagnosed on clinical and histological grounds as gestational, to be of genetically non-maternal (androgenic) origin. The neoplasm previously classified as a non-gestational choriocarcinoma was demonstrated to be of maternal origin, as were the non-germ cell reproductive tract tumors. Samples from hydatidiform moles contained either androgenic markers only or a mix of maternal and androgenic markers, as previously seen in complete and partial moles, respectively.

CONCLUSION

A commercially available microsatellite DNA diagnostic assay is a quick and convenient way to discriminate between gestational and non-gestational choriocarcinoma.

Molar gestations and hydropic abortions differentiated by p57 immunostaining

Classification of molar gestations into complete and partial and their differentiation from hydropic abortions traditionally are accomplished by morphology alone. The process sometimes may be inaccurate or inconclusive. With the availability of p57 immunostaining it may be possible to objectively classify these lesions. We used p57 for the differential diagnosis of hydropic abortions and molar gestations and correlated the findings with the clinical outcome of patients in each category. First, 86 cases were originally classified by histomorphology into hydropic abortion (42) and molar gestations (23 complete and 21partial). Based on the pattern of p57 staining the cases were reclassified into 45 hydropic abortions, 15 partial moles and 26 complete moles (3 cases with previous diagnosis of complete mole based on morphology were reclassified as hydropic abortion). Clinical follow-ups ranged from 6-24 months and showed persistent trophoblastic disease in 8 cases (31%) of complete moles and 3 cases (20%) of partial moles (p = 0.47). No hydropic abortion cases demonstrated persistent trophoblastic disease. One patient with partial mole developed choriocarcinoma. This study confirms that p57 objectively distinguishes hydropic abortions from molar gestations (partial and complete moles). This differentiation is clinically relevant since patients with hydropic abortions do not need to be followed while patients with molar gestations do.

Analysis of gestational trophoblastic disease by genotyping and chromosome in situ hybridization

Hydatidiform mole is classified into partial and complete subtypes according to histopathological and genetic criteria. Distinction between the two by histology alone may be difficult. Genetically, a complete mole is diploid without maternal contribution, whereas a partial mole is triploid with a maternal chromosome complement. To assess the accuracy of histological diagnosis by correlating with the genetic composition, we performed fluorescent microsatellite genotyping to detect the presence or absence of maternal genome in a hydatidiform mole and carried out chromosome in situ hybridization to analyze the ploidy. For genotyping analysis, paraffin sections of 36 complete and nine partial moles, diagnosed according to histological criteria, were microdissected and DNA was separately extracted from the decidua and molar villi. Six pairs of primers that flank polymorphic microsatellite repeat sequences on five different chromosomes were used. In all, 34 cases, including 31 complete moles and three partial moles diagnosed histologically, showed no maternal contribution by genotyping; thus these could be genetically considered as complete mole. The other 11 cases (five complete moles and six partial moles previously diagnosed by histology) showed the presence of maternal contribution and were genetically diagnosed as partial moles. The genotyping results correlated with histological evaluation in 88% (37/45) of hydatidiform mole and correlated with chromosome in situ hybridization findings in all the cases, that is, triploid hydatidiform moles had maternal-derived alleles, while diploid hydatidiform moles were purely androgenetic. Compared with genetic diagnosis, histological evaluation was more reliable for the diagnosis of a complete mole (91%, 31/34) than that of a partial mole (55%, 6/11) (P=0.0033). Seven complete moles and three partial moles diagnosed genetically developed gestational trophoblastic neoplasia. To conclude, genotyping and chromosome in situ hybridization can provide reliable adjunct to histology for the classification of a hydatidiform mole, especially in cases with difficult histological evaluation and early gestational age. As a partial mole still carries a risk of developing gestational trophoblastic neoplasia, follow-up is considered necessary for both complete and partial moles.