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Introduction

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Gestational trophoblastic disease (GTD) is the term used to encompass a group of tumors typified by abnormal trophoblast proliferation. Trophoblast produce human chorionic gonadotropin (hCG), thus the measurement of this peptide hormone in serum is essential for GTD diagnosis, management, and surveillance. GTD histologically is divided into hydatidiform moles, which are characterized by the presence of villi, and nonmolar trophoblastic neoplasms, which lack villi.

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Hydatidiform moles are excessively edematous immature placentas (Benirschke, 2012). These include the benign complete hydatidiform mole and partial hydatidiform mole and the malignant invasive mole. Invasive mole is deemed malignant due to its marked penetration into and destruction of the myometrium as well as its ability to metastasize.

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Nonmolar trophoblastic neoplasms include choriocarcinoma, placental site trophoblastic tumor, and epithelioid trophoblastic tumor. These three are differentiated by the type of trophoblast they contain.

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The malignant forms of gestational trophoblastic disease are termed gestational trophoblastic neoplasia (GTN). These include invasive mole, choriocarcinoma, placental site trophoblastic tumor, and epithelioid trophoblastic tumor. Other terms applied to GTN are malignant gestational trophoblastic disease and persistent gestational trophoblastic disease. These malignancies develop weeks or years following any type of pregnancy, but frequently occur after a hydatidiform mole.

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Each of the GTN tumor types is histologically distinct and varies in its propensity to invade and metastasize. However, histological confirmation is typically not available. Instead, measurement of serum hCG levels combined with clinical findings—rather than a histological specimen—is used to diagnose and treat this malignancy. Accordingly, GTN is often identified and effectively treated as a group.

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In the past, these metastatic tumors had a prohibitively high mortality rate. However, with chemotherapy, currently most tumors are highly curable (Goldstein, 2010). Early-stage GTN is typically cured with single-agent chemotherapy, whereas later-stage disease usually responds to combination chemotherapy.

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Hydatidiform Mole—Molar Pregnancy

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The classic histological findings of molar pregnancy include villous stromal edema and trophoblast proliferation (Fig. 20-1). The degree of histological changes, karyotypic differences, and the absence or presence of embryonic elements are used to classify them as either complete or partial moles. These two also vary in associated risks for developing medical comorbidities and postevacuation GTN. Of the two, GTN more frequently follows complete hydatidiform mole.

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Figure 20-1

Complete hydatidiform mole. A. Gross specimen with characteristic vesicles of variable size. (Image contributed by Dr. Brian Levenson.) B. Low-magnification photomicrograph shows generalized edema and cistern formation (black asterisks) within avascular villi. Haphazard trophoblastic hyperplasia is marked by a yellow asterisk on the right. (Image contributed by Dr. Erika Fong.)

Graphic Jump Location
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A complete mole has abnormal chorionic villi that grossly appear as a mass of clear vesicles. These vary in size and often hang in clusters from thin pedicles. In contrast, ...

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