GTN - definition, risk factor and management in MS obstetrics
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Gestational Trophoblastic Neoplasia (GTN)
Definition
Gestational trophoblastic neoplasia (GTN) refers to the malignant subset of gestational trophoblastic disease (GTD) - a group of interrelated tumors arising from abnormal proliferation of placental trophoblasts with varying propensities for local invasion and metastasis.
GTD spectrum:
- Benign: Hydatidiform mole (complete and partial)
- Malignant (= GTN):
- Invasive mole
- Choriocarcinoma
- Placental-site trophoblastic tumor (PSTT)
- Epithelioid trophoblastic tumor (ETT)
GTN is one of the rare human malignancies curable even in the presence of widespread metastasis. GTN can occur after any gestational event - molar pregnancy, induced/spontaneous abortion, ectopic pregnancy, or term delivery.
- Berek & Novak's Gynecology, p. 2493
Risk Factors for GTN
1. Antecedent Pregnancy Type
GTN most commonly follows molar pregnancy but can occur after any pregnancy event. Risk by antecedent:
- Complete hydatidiform mole: 15-20% risk of persistent GTN
- Partial hydatidiform mole: 1-5% risk
- Non-molar pregnancies (term delivery, abortion): lower but real risk - Creasy & Resnik's Maternal-Fetal Medicine, p. 1356
2. High-Risk Features After Complete Mole
A review of 858 complete moles at the New England Trophoblastic Disease Center (NETDC) identified the following high-risk signs:
| High-Risk Sign | Prognostic Significance |
|---|---|
| hCG > 100,000 mIU/mL | Local invasion in 31%, metastasis in 8.8% of high-risk group |
| Excessive uterine enlargement | vs. local invasion only 3.4% in low-risk |
| Theca-lutein cysts ≥6 cm | Metastasis in 0.6% of low-risk group |
3. Age
- Older patients carry substantially higher risk
- Persistent GTN after complete mole: 37% in women >40 years, 60% in women >50 years
- Age >39 scores 1 point in the WHO Prognostic Scoring System
4. Other Epidemiological Risk Factors (for molar pregnancy leading to GTN)
-
Extremes of reproductive age
-
Prior molar pregnancy (risk of recurrent mole: 1-1.5% after one; rises after two)
-
History of prior miscarriage
-
Geographic/ethnic background (incidence highest in Asia: 2:1,000 in Japan; 1:1,500 in United States)
-
Berek & Novak's Gynecology, p. 2504, 2532; Creasy & Resnik's Maternal-Fetal Medicine, p. 1355-1356
Staging and Prognostic Scoring
FIGO Anatomic Staging
| Stage | Description |
|---|---|
| I | Confined to uterus |
| II | GTN extends outside uterus but limited to genital structures |
| III | GTN extends to lungs (with/without genital tract involvement) |
| IV | All other metastatic sites |
WHO Prognostic Scoring System (Modified)
Determines Low Risk (score <7) vs High Risk (score ≥7):
| Factor | 0 | 1 | 2 | 4 |
|---|---|---|---|---|
| Age (years) | ≤39 | >39 | - | - |
| Antecedent pregnancy | Hydatidiform mole | Abortion | Term | - |
| Interval to chemotherapy (months) | <4 | 4-6 | 7-12 | >12 |
| Pretreatment hCG (IU/L) | <10³ | 10³-10⁴ | 10⁴-10⁵ | >10⁵ |
| ABO blood group | - | O or A | B or AB | - |
| Largest tumor size (cm) | <3 | 3-5 | >5 | - |
| Site of metastases | - | Spleen, kidney | GI tract | Brain, liver |
| Number of metastases | - | 1-3 | 4-8 | >8 |
| Prior chemotherapy | - | - | 1 drug | ≥2 drugs |
- Berek & Novak's Gynecology, p. 2511
Diagnosis of GTN After Molar Evacuation
GTN is diagnosed biochemically when any of the following occur after molar evacuation:
- Plateau of hCG (±10% over 4 values across 3 weeks)
- Rise of hCG (>10% over 3 values across 2 weeks)
- Elevated hCG >6 months after evacuation
- Histologic diagnosis of choriocarcinoma
Diagnostic workup for confirmed GTN:
- Complete history and physical examination
- Serum hCG level
- Hepatic, thyroid, renal function tests
- CBC with differential
- Chest X-ray or CT chest
- Ultrasound or CT abdomen/pelvis
- CT/MRI brain (if metastatic disease or choriocarcinoma)
- Plasma-to-CSF hCG ratio: <60 suggests cerebral metastasis
Note on Phantom hCG: False-positive serum hCG from heterophilic antibodies can mimic GTN. Exclude by running a simultaneous urine hCG (these antibodies are not excreted in urine) or by serial dilution.
- Berek & Novak's Gynecology, p. 2511; Creasy & Resnik's Maternal-Fetal Medicine, p. 1356
Management of GTN
Protocol by Stage (Table 41-4, Berek & Novak's)
| Stage | Risk | Initial Treatment | Resistant Disease |
|---|---|---|---|
| Stage I | - | Single-agent chemo OR hysterectomy + adjuvant chemo | Combination chemo, hysterectomy, local resection, pelvic infusion |
| Stages II-III | Low (<7) | Single-agent chemo | Combination chemo |
| Stages II-III | High (≥7) | Combination chemo | Second-line combination chemo |
| Stage IV | - | Combination chemo | Second-line combination chemo, hepatic arterial infusion |
Low-Risk GTN (Stage I; Stages II-III, score <7)
Option 1 - Fertility desired:
- Single-agent chemotherapy - methotrexate (MTX) or actinomycin-D (Act-D)
- MTX regimens: 8-day MTX/folinic acid, weekly MTX IM, 5-day MTX
- Act-D: 5-day or pulsed regimen
- Remission rate with single-agent: very high (>80-90%)
Option 2 - Fertility not desired:
- Hysterectomy + adjuvant single-agent chemotherapy (concurrent, not sequential)
- Rationale: reduces viable cell dissemination at surgery, maintains cytotoxic levels, treats occult metastases
- In one NETDC series of 31 patients, 100% achieved complete remission with primary hysterectomy + single-agent chemo
PSTT and ETT (Stage I): Hysterectomy is preferred - these tumors are relatively chemoresistant
High-Risk GTN (Stages II-IV, score ≥7)
EMA-CO is the standard regimen:
- Etoposide
- Methotrexate
- Actinomycin-D
- Cyclophosphamide
- Oncovin (vincristine)
For brain metastases: Whole-brain radiation (3,000 cGy) + craniotomy if needed for complications
For liver metastases: Resection or embolization for complications
Post-Remission hCG Surveillance
- After molar evacuation: hCG weekly until normal x3 weeks, then monthly
- Standard surveillance: 6 months (shorter duration may be safe especially after partial mole, given risk of GTN after hCG becomes undetectable is ≤0.2%)
- Referral to gynecologic oncology if hCG plateaus, rises, or persists >6 months
Subsequent Pregnancies
GTN treatment does not impair future fertility:
- After complete mole (NETDC data, 1,388 pregnancies): 68.4% term births, 7.4% premature, 18.4% spontaneous abortion, 1.4% repeat molar pregnancy
- After GTN treated with chemotherapy (NETDC, 667 pregnancies): 66.9% term births, 18.4% spontaneous abortion - congenital malformation rate not increased despite chemotherapy exposure
Recommendations for subsequent pregnancies:
- First-trimester pelvic ultrasound to confirm normal development
- hCG level 6 weeks after delivery to exclude occult trophoblastic neoplasia
- Berek & Novak's Gynecology, p. 2521; Creasy & Resnik's Maternal-Fetal Medicine, p. 1356
Key Takeaway for MS Obstetrics: GTN is biochemically diagnosed by hCG monitoring after molar evacuation. The WHO prognostic score stratifies disease into low-risk (single-agent chemo) vs. high-risk (EMA-CO). Even metastatic disease carries excellent cure rates. Phantom hCG must be excluded. Subsequent reproductive outcomes are reassuring.
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