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

Abstract

Distinction of hydatidiform moles (HM) from nonmolar specimens and subclassification of HMs as complete hydatidiform mole (CHM), partial hydatidiform mole (PHM), or early CHM (eCHM) are important for clinical practice and investigational studies but diagnosis based solely on morphology suffers from poor interobserver reproducibility. Recent studies have demonstrated the use of p57 immunostaining and molecular genotyping for improving diagnosis of HMs. After performing a validation study of both techniques on 24 archival products of conception specimens (7 CHMs, 8 PHMs, 9 nonmolar), we prospectively analyzed 42 cases, largely obtained from a gynecologic pathology consultation practice, for which there was any consideration of a diagnosis of HM. After satisfactory experience with prospective cases, a modified approach was adopted, with p57 immunostaining used in conjunction with morphology to triage cases for molecular genotyping. Final diagnoses for the prospective cases based on combined morphology and ancillary testing were 24 CHMs (including 7 eCHMs), 7 PHMs, and 11 nonmolar specimens. P57 immunostaining, performed on all 66 cases, was negative in all CHMs, with the exception of 1 case of molecularly confirmed CHM with diffuse p57 expression, and positive in all PHMs and nonmolar specimens, with the exception of 3 cases of molecularly confirmed PHMs with an equivocal extent of p57 expression. Molecular genotyping of 51 cases (24 validation, 27 prospective) yielded data consistent with p57 results in the 47 cases with unequivocal p57 expression patterns and was used to establish the diagnoses for the 4 cases with aberrant or equivocal p57 results. All 17 genotyped CHMs demonstrated androgenetic diploidy, including the CHM with retained p57 expression; this case also demonstrated trisomy of chromosome 11 (retained maternal allele), accounting for the aberrant p57 expression. The remaining 14 CHMs were diagnosed by morphology and negative p57 results alone. All 15 PHMs demonstrated diandric triploidy. All genotyped nonmolar specimens demonstrated biparental diploidy. This study validates p57 immunostaining as a prospectively applicable triage assay for the diagnosis of CHMs based on morphology and a negative p57 result. Molecular genotyping is validated as a method to confirm a diagnosis of CHM by demonstrating androgenetic diploidy and to resolve p57-positive cases into diandric triploid PHMs, biparental diploid nonmolar specimens, and the rare CHM with aberrant p57 expression.

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

“…However, previous studies have demonstrated that diagnosis of hydatidiform moles based on morphology alone, even by experienced pathologists with specialized training, is subject to interobserver variability and therefore suboptimal diagnostic reproducibility. [9][10][11][12][13][14][15] A number of studies have demonstrated the value of ancillary techniques, including immunohistochemical analysis of cyclin-dependent kinase inhibitor 1C (CDKN1C/p57/Kip2, the protein product of the CDKN1C imprinted gene located at chromosome 11p15.5; referred to henceforth as p57) expression [16][17][18][19][20][21][22][23][24][25][26][27] and molecular genotyping via PCR amplification of short tandem repeat loci, 23,25,[28][29][30][31] for improving the diagnosis of hydatidiform moles. Genotyping is particularly valuable because it allows for specific distinction of complete hydatidiform moles, partial hydatidiform moles, and nonmolar specimens from one another due to their unique genetics.…”

Accuracy of p57KIP2 compared with genotyping to diagnose complete hydatidiform mole: a systematic review and meta‐analysis

“…Seven publications met the eligibility criteria and were included in the systematic review 1, 8, 12, 13, 20, 21, 22. The basic characteristics of the included studies were study sample size ranging from 16 to 80 women with ages ranging from 13 to 55 years old (Supporting Information Appendix S3).…”

“…The Popiolek et al10 study found that p57 KIP2 immunostaining accurately identified all the investigated cases of CHM and concluded that the test is a time‐ and cost‐effective means of distinguishing CHM from its mimics in challenging cases. The McConnell et al13 study validated p57 KIP2 immunostaining as a triage assay for the diagnosis of CHM and the genotyping as a confirmatory assay. The Vang et al21 study states that p57 KIP2 immunostaining improves the sensitivity of a diagnosis of CHM in 96% from morphological diagnosis.…”

“…Three of the studies refer to the same population 12, 21. and only two of these studies13, 21 provided quantitative data, we used only the most recent data published21 to avoid duplication. Eligible studies for the quantitative analysis included 126 pregnant women.…”

“…Differentiating a molar pregnancy from nonmolar specimens (NMS) and the classification of HM as CHM (including early CHM), PHM, or hydropic miscarriage are important for both clinical practice and investigational studies because of the risk of development of gestational trophoblastic neoplasia (GTN), including choriocarcinoma, which is significantly higher after a pregnancy affected by CHM (15–27%) or PHM (0.5–5%) then with any other pregnancy 10, 11, 12, 13…”