Gestational Trophoblastic Disease: Contemporary Diagnostic Approach

Triaging and Evaluation of Products of Conception in Abortions and Post-Partum Hemorrhage

The proper evaluation of abortion specimens and placentas from stillbirth and post-partum cases is important for adequate clinical care of post-abortion and post-partum patients. The following topics will be reviewed: (1) the importance of evaluation of both fetal and placental tissue in first trimester abortions to confirm an intrauterine pregnancy versus an ectopic pregnancy; (2) the clinical history associated with an abortion specimen or retained products of conception (POC) influences how the pathologist should triage the specimen; (3) the criteria for diagnosis of a molar pregnancy, which is critical for clinicians to know which patients need follow-up; (4) the utility of genetic studies for both diagnosis and appropriate follow-up of the patient; and (5) the pathologic evaluation of specimens from patients with post-partum hemorrhage for placenta accreta spectrum and subinvolution of maternal vessels.

When to Consult a Geneticist Specialising in Gestational Trophoblastic Disease

BACKGROUND

Gestational trophoblastic disease comprises hydatidiform moles and a rare group of malignancies that derive from trophoblasts. Although there are typical morphological features that may distinguish hydatidiform moles from non-molar products of conception, such features are not always present, especially at early stages of pregnancy. Furthermore, mosaic/chimeric pregnancies and twin pregnancies make pathological diagnosis challenging while trophoblastic tumours can also pose diagnostic problems in terms of their gestational or non-gestational origin.

OBJECTIVES

The aim of this study was to show that ancillary genetic testing can be used to aid diagnosis and clinical management of GTD.

METHODS

Each author identified cases where genetic testing, including short tandem repeat (STR) genotyping, ploidy analysis, next-generation sequencing, and immunostaining for p57, the product of the imprinted gene CDKN1C, facilitated accurate diagnosis and improved patient management. Representative cases were chosen to illustrate the value of ancillary genetic testing in different scenarios.

OUTCOME

Genetic analysis of placental tissue can aid in determining the risk of developing gestational trophoblastic neoplasia, facilitating discrimination between low risk triploid (partial) and high risk androgenetic (complete) moles, discriminating between a hydatidiform mole twinned with a normal conceptus and a triploid conception and identification of androgenetic/biparental diploid mosaicism/chimerism. STR genotyping of placental tissue and targeted gene sequencing of patients can identify women with an inherited predisposition to recurrent molar pregnancies. Genotyping can distinguish gestational from non-gestational trophoblastic tumours using tissue or circulating tumour DNA and can also identify the causative pregnancy which is the key prognostic factor for placental site and epithelioid trophoblastic tumours.

CONCLUSIONS AND OUTLOOK

STR genotyping and p57 immunostaining have been invaluable to the management of gestational trophoblastic disease in many situations. The use of next-generation sequencing and of liquid biopsies is opening up new pathways for GTD diagnostics. Development of these techniques has the potential to identify novel biomarkers of GTD and further refine diagnosis.

Intact Chorionic Vesicle in Very Early Products of Conception Specimens: Clinicopathologic Features of 26 Cases That May Mimic Complete Hydatidiform Mole

Among the morphologic mimics of hydatidiform moles, the chorionic vesicle of early first-trimester pregnancy has received scant attention. The chorionic vesicle is the stage of the implanted blastocyst in which the cytotrophoblastic shell is circumferentially lined by primary and secondary villi and envelops the notochord stage embryo, yolk sac, and amniotic sac, ∼5 to 6 weeks since the last menstrual period. Miscarriage specimens at this early gestational age that contain an intact chorionic vesicle may be misinterpreted as a complete hydatidiform mole because of its large size, cistern-like cavity, and circumferentially radiating villi and trophoblast, particularly so when embryonic tissue is absent. We present the clinicopathologic features of 26 products of conception specimens containing a chorionic vesicle, some of which were submitted for consultation as a possible complete mole. The median gestational age was 6 weeks. The majority were free-floating in the specimen, unattached to endometrium. The median diameter was 6.3 mm and ranged up to 11.3 mm. The embryo was absent in 81% of cases, leaving an empty cavity resembling the cistern of a complete mole in all but 2 cases. Most cases exhibited circumferential villi and variable degrees of proliferating polarized villous trophoblast and extravillous trophoblast but trophoblast atypia was absent. Villous stromal karyorrhexis and blue-gray myxoid extracellular stromal matrix were observed in the majority of cases. A minority exhibited focal abnormal villous morphology concerning for early molar pregnancy, including irregular projections (27%), invaginations (12%), or bulbous shapes (4%) of the villous contours and trophoblast pseudoinclusions (15%). In contrast, orderly hierarchical branching of the secondary villi occurred in 31%. p57 immunoexpression was intact in all 25 cases tested. Short tandem repeat genotype testing confirmed a biparental diploid genotype in both of 2 cases tested. Although uncommonly observed in early first-trimester products of conception specimens, the normal chorionic vesicle merits awareness as a potential diagnostic pitfall. While some morphologic features resemble those of a well-developed complete mole, at this early gestational age such features are not expected in a very early complete mole. Attention to the reported gestational age, if available, and presence of embryonic tissues will mitigate against misclassification as complete mole. As with the workup of any potential gestational trophoblastic disease, partnering the clinical and morphologic evaluation with molecular evaluation (intact p57 immunoexpression and lack of any of the characteristic molar genotypes) offers the most precise classification.

Advances in the diagnosis and early management of gestational trophoblastic disease

Gestational trophoblastic disease describes a group of rare pregnancy related disorders that span a spectrum of premalignant and malignant conditions. Hydatidiform mole (also termed molar pregnancy) is the most common form of this disease. Hydatidiform mole describes an abnormal conceptus containing two copies of the paternal genome, which is classified as partial when the maternal genome is present or complete when the maternal genome is absent. Hydatidiform mole typically presents in the first trimester with irregular vaginal bleeding and can be suspected on ultrasound but confirmation requires histopathological evaluation of the products of conception. Most molar pregnancies resolve without treatment after uterine evacuation, but occasionally the disease persists and develops into gestational trophoblastic neoplasia. Close monitoring of women after molar pregnancy, with regular measurement of human chorionic gonadotrophin concentrations, allows for early detection of malignancy. Given the rarity of the disease, clinical management and treatment is best provided in specialist centres where very high cure rates are achievable. This review looks at advances in the diagnosis and early management of gestational trophoblastic disease and highlights updates to disease classification and clinical guidelines. Use of molecular genotyping for improved diagnostic accuracy and risk stratification is reviewed and future biomarkers for the earlier detection of malignancy are considered.