Gestational trophoblastic disease (GTD) refers to a spectrum of interrelated but histologically distinct tumors originating from the placenta (Table 10-1). These diseases are characterized by a reliable tumor marker, the β-subunit of human chorionic gonadotropin (β-hCG), and have varying tendencies toward local invasion and metastasis.
TABLE 10-1.Modified WHO Classification of GTD ||Download (.pdf) TABLE 10-1. Modified WHO Classification of GTD
Placental site trophoblastic tumor
Epithelioid trophoblastic tumor
Gestational trophoblastic neoplasia (GTN) refers to a subset of GTD that develops malignant sequelae. These tumors require formal staging and typically respond very favorably to chemotherapy. GTN develops most commonly after a molar pregnancy, yet it may follow any gestation—including a normal term delivery. The prognosis is excellent with rare exceptions, and patients are routinely cured even in the presence of widespread disease. Moreover, fertility can be preserved in virtually all cases. The likelihood of a successful subsequent pregnancy outcome is equally bright (Vargas, 2014; Williams, 2014; Wong, 2014). Accordingly, although gestational trophoblastic disease is uncommon, it is so intimately related to pregnancy that clinicians practicing obstetrics should be familiar with its presentation, diagnosis, and management.
EPIDEMIOLOGY AND RISK FACTORS
The incidence of gestational trophoblastic disease has remained fairly constant at approximately 1 to 2 per 1000 deliveries in North America and Europe (Drake, 2006; Loukovaara, 2005; Lybol, 2011). A similar frequency has been observed in South Africa and Turkey (Cakmak, 2014; Moodley, 2003). Although historically higher incidence rates have been reported in parts of Asia, this may have largely reflected discrepancies between population-based and hospital-based data collection (Kim, 2004). Improved socioeconomic conditions and dietary changes may also be partly responsible. That said, Hispanics and Native Americans living in the United States reportedly do have an increased incidence, as do certain population groups living in Southeast Asia (Drake, 2006; Smith, 2003; Tham, 2003). In at least one study, GTN was found to be more aggressive in Asian women (Maesta, 2015).
Of other risk factors, the upper and lower extremes of maternal age have classically been associated with a higher risk of developing GTD (Altman, 2008; Loukovaara, 2005). This association is much greater for complete moles, whereas the risk of partial molar pregnancy varies relatively little with age. Moreover, compared with the risk of those with maternal age of 15 years or younger, the degree of risk is much greater for women 45 years (1 percent) or older (17 percent at age 50) (Savage, 2010; Sebire, 2002a). One explanation may relate to ova from older women having higher rates of abnormal fertilization. Similarly, older paternal age has also been associated with elevated risk (La Vecchia, 1984; Parazzini, 1986).