What is GTN (Gestational Trophoblastic Neoplasia)?
GTN refers to the malignant forms of gestational trophoblastic disease—a group of highly curable cancers that arise from placental tissue and include invasive mole, choriocarcinoma, placental site trophoblastic tumor (PSTT), and epithelioid trophoblastic tumor (ETT). 1
Key Defining Features
GTN represents the malignant subset within the broader category of gestational trophoblastic disease (GTD). While hydatidiform moles (complete and partial) are benign/premalignant and comprise 80% of all GTD, GTN encompasses the frankly malignant entities that develop either after molar pregnancies or following normal/abnormal gestations 1.
The Four Types of GTN
1. Invasive Mole (15% of GTD)
- Arises from extension of hydatidiform mole into the myometrium via tissue or venous channels
- Develops in 15-20% of complete moles but only 1-5% of partial moles
- Approximately 15% metastasize to lung or vagina
- Diagnosed by persistently elevated hCG after molar evacuation 1
2. Choriocarcinoma (Part of the 5% rarer GTN)
- Develops from villous trophoblast with abnormal trophoblastic hyperplasia and anaplasia
- Characterized by hCG production, absence of chorionic villi, hemorrhage, and necrosis
- Can follow any pregnancy type: 50% after hydatidiform mole, 25% after term/preterm gestation, 25% after ectopic pregnancy or abortion
- Only 2-3% of hydatidiform moles progress to choriocarcinoma 1
3. Placental Site Trophoblastic Tumor (PSTT)
- Extremely rare (1 in 100,000 pregnancies, representing ~1% of all GTN)
- Arises from interstitial trophoblast at placental implantation site
- Presents months to years after the antecedent pregnancy (usually nonmolar)
- Less vascular invasion, necrosis, and hemorrhage than choriocarcinoma
- Lower hCG levels than other GTN types 1
4. Epithelioid Trophoblastic Tumor (ETT)
- Rare variant of PSTT that simulates carcinoma
- Develops from neoplastic transformation of chorionic-type intermediate trophoblast
- Typically presents years after term delivery 1
Clinical Significance
The critical distinction is that GTN is highly curable with cure rates approaching 100% for low-risk disease and >95% for high-risk disease when treated at specialized centers 1, 2. Treatment typically preserves fertility 1.
Diagnostic Criteria for GTN
GTN is diagnosed after hydatidiform mole evacuation when hCG monitoring shows 1:
- hCG plateau for 4 consecutive values over 3 weeks
- hCG rise >10% for 3 consecutive values over 2 weeks
- hCG persistence 6 months or more after molar evacuation
- Histopathologic diagnosis of choriocarcinoma
- Evidence of metastatic disease
Common Pitfall
Do not confuse GTN with GTD—GTD is the umbrella term encompassing both benign (hydatidiform moles) and malignant (GTN) forms. All GTD requires hCG surveillance, but only GTN requires chemotherapy or more aggressive intervention 1, 3.