Gestational Trophoblastic Neoplasia (GTN)

Gestational trophoblastic neoplasia is the malignant end of the gestational trophoblastic disease (GTD) spectrum — the group of tumours that arise from placental trophoblast and are exquisitely chemo-sensitive and beta-hCG-trackable. For NEET PG, the marrow of this topic is the FIGO anatomical staging + modified WHO prognostic score, the low- vs high-risk treatment split (single-agent vs EMA-CO), beta-hCG surveillance, and the few "different" tumours (PSTT, ETT) that break the usual rules.

Definition & classification

Gestational trophoblastic disease (GTD) is an umbrella for proliferative disorders of trophoblast. GTN is the subset that is locally invasive or metastatic and requires treatment beyond evacuation.

GTN may follow any pregnancy event — molar (most common), abortion, ectopic, or even a normal-term pregnancy. The key conceptual point is that GTN is one of the few human malignancies that can be diagnosed and treated without histology — on the basis of a rising or plateauing beta-hCG alone.

Lesion	Nature	Notes
Complete hydatidiform mole	Benign (premalignant)	46,XX (paternal only); ~15–20% progress to GTN
Partial hydatidiform mole	Benign (premalignant)	69,XXY triploid; ~1–5% progress to GTN
Invasive mole (chorioadenoma destruens)	Malignant — local	Molar villi invade myometrium; most common GTN, usually post-molar
Choriocarcinoma	Malignant — aggressive	No villi; sheets of cyto- & syncytiotrophoblast; early haematogenous spread
Placental-site trophoblastic tumour (PSTT)	Malignant — special	Intermediate trophoblast; secretes hPL; relatively chemo-RESISTANT
Epithelioid trophoblastic tumour (ETT)	Malignant — rare	Chorionic-type intermediate trophoblast; mimics cervical SCC

High-yield: Invasive mole is the commonest form of GTN, but choriocarcinoma is the one that classically presents with widespread metastases (lung, vagina, brain, liver) and can follow a normal term pregnancy (≈1 in 50,000 term births).

High-yield: PSTT and ETT arise from intermediate trophoblast, produce low beta-hCG relative to bulk, are NOT chemo-sensitive, and are treated primarily by hysterectomy. They do not get scored on the WHO system.

Etiology & pathophysiology

• Antecedent pregnancy: ~50% of choriocarcinomas follow a molar pregnancy, ~25% follow abortion/ectopic, ~25% follow a term pregnancy.
• Risk factors: extremes of maternal age (<16 and >40 yr, especially >45), prior molar pregnancy, blood group A women × group O partners (classic for choriocarcinoma), dietary deficiency (carotene/vitamin A) in endemic regions (South-East Asia higher incidence).
• Pathogenesis: trophoblast normally invades and remodels spiral arteries; in GTN this invasive, angiogenic, immune-evading capacity becomes unchecked. Rich vascularity explains the haematogenous spread pattern and the tendency to haemorrhage (vaginal mets bleed catastrophically if biopsied — do not biopsy vaginal metastases).
• Histology distinction: invasive mole retains chorionic villi invading myometrium; choriocarcinoma has no villi — only malignant trophoblast with central haemorrhage/necrosis.

High-yield: Never biopsy a suspected vaginal metastasis of GTN — they are highly vascular and bleed torrentially.

Clinical features

The most common scenario is the woman with persistent or abnormal bleeding after evacuation of a molar pregnancy, or after any pregnancy event with a plateauing/rising hCG.

• Irregular vaginal bleeding (commonest), enlarged subinvoluted uterus.
• Theca-lutein cysts (bilateral ovarian, hCG-driven) that fail to regress.
• Symptoms from metastases:
  • Lung (commonest metastatic site): haemoptysis, cough, dyspnoea, pleuritic pain; CXR cannonball/snowstorm shadows.
  • Vagina (second commonest): bluish/purple sub-urethral nodules — bleed profusely.
  • Brain: headache, seizures, focal deficit (poor-prognosis marker).
  • Liver: RUQ pain (poor-prognosis marker).
• Rarely: hyperthyroidism (hCG cross-reacts with TSH receptor), early pre-eclampsia, hyperemesis.

High-yield: Order of metastatic frequency: Lung > Vagina > Brain/Liver. Brain and liver involvement upgrade the prognostic score sharply (4 points each) and define high-risk disease.

Diagnosis & investigation of choice

GTN after a molar pregnancy is diagnosed biochemically using serial quantitative serum beta-hCG. The 2002 FIGO/WHO criteria for diagnosing post-molar GTN — memorise these:

1. Plateau of hCG (±10%) across 4 values over 3 weeks (days 1, 7, 14, 21).
2. Rise in hCG >10% across 3 values over 2 weeks (days 1, 7, 14).
3. hCG persistently detectable for ≥6 months after molar evacuation.
4. Histological diagnosis of choriocarcinoma.

High-yield: Any one of these four criteria establishes the diagnosis of GTN — no tissue is required for the first three.

Investigation of choice / work-up flow:

Serial serum beta-hCG (diagnosis + the tumour marker) → pelvic USG with Doppler (myometrial invasion, vascularity) → CXR (first-line for lung mets and for counting "lung metastases" in the score) → CT chest if CXR clear but suspicion high → CT/MRI brain + CT abdomen-pelvis in high-risk or proven metastatic disease.

• Beta-hCG is both diagnostic marker and the basis of treatment monitoring; its half-life is ~24–36 hours.
• CXR is used to count lung metastases for the prognostic score (CT-only micrometastases are NOT counted).
• A lumbar CSF:serum hCG ratio >1:60 suggests occult CNS disease.

High-yield: Beware the phantom hCG / false-positive hCG (heterophile antibodies). Suspect it when serum hCG is positive but urine hCG is negative and there is no rise/fall with treatment — confirm by serial dilution. Avoids needless chemotherapy.

Staging & prognostic scoring — the core MCQ

GTN uses two systems together: FIGO anatomical stage (I–IV) and the modified WHO prognostic score.

FIGO stage	Extent
I	Disease confined to the uterus
II	Extends outside uterus but limited to genital structures (adnexa, vagina, broad ligament)
III	Extends to lungs (± genital involvement)
IV	All other metastatic sites (brain, liver, kidney, GI)

Modified WHO prognostic scoring index (each parameter scored 0/1/2/4):

Prognostic factor	0	1	2	4
Age (yr)	<40	≥40	—	—
Antecedent pregnancy	Mole	Abortion	Term	—
Interval (months) from pregnancy	<4	4–6	7–12	>12
Pre-treatment beta-hCG (IU/L)	<10³	10³–10⁴	10⁴–10⁵	>10⁵
Largest tumour size (incl. uterus)	<3 cm	3–4 cm	≥5 cm	—
Site of metastases	Lung	Spleen, kidney	GI tract	Brain, liver
Number of metastases	0	1–4	5–8	>8
Prior failed chemotherapy	—	—	Single drug	≥2 drugs

Interpretation:

• Score ≤6 → LOW-risk GTN → single-agent chemotherapy.
• Score ≥7 → HIGH-risk GTN → multi-agent chemotherapy (EMA-CO).

High-yield: The cut-off is 7. ≤6 = low risk; ≥7 = high risk. A common stem reports an isolated factor (e.g., brain mets = 4 points alone) — but you must total all eight factors.

High-yield: Maximum score on a single factor (interval >12 mo, hCG >10⁵, brain/liver mets, >8 mets, ≥2 prior drugs) is 4. Antecedent term pregnancy and >12-month interval flag higher risk because they correlate with choriocarcinoma.

Management / drug of choice

Management is dictated entirely by the risk stratification. Surgery is supportive in chemo-sensitive disease and primary only for PSTT/ETT.

Low-risk GTN (WHO ≤6) — single agent

Drug of choice: single-agent chemotherapy — methotrexate (with folinic acid rescue) OR actinomycin-D (dactinomycin).

• Methotrexate–folinic acid (MTX-FA) 8-day regimen is the most-used first line.
• Actinomycin-D (pulsed) is preferred when liver/renal dysfunction contraindicates MTX, or after MTX failure; it has a slight edge in efficacy but more toxicity (alopecia, nausea).
• Switch to the alternate single agent if hCG plateaus on the first; switch to multi-agent (EMA-CO) if it resists both.
• Continue chemotherapy until hCG normalises, then give 2–3 consolidation cycles to eradicate microscopic disease and prevent relapse.

High-risk GTN (WHO ≥7) — multi-agent

Regimen of choice: EMA-CO — given weekly/alternate-day in cycles.

EMA-CO = Etoposide + Methotrexate + Actinomycin-D (EMA) / Cyclophosphamide + Oncovin (Vincristine) (CO).

High-yield mnemonic — EMA-CO: Etoposide, Methotrexate, Actinomycin-D // Cyclophosphamide, Oncovin (vincristine). Cure rates for high-risk disease are ~85–95%.

• Brain metastases: add intrathecal methotrexate ± whole-brain radiotherapy, or use a high-dose MTX CNS protocol (EMA-CO with augmented MTX).
• Ultra-high-risk / EMA-CO failure: salvage with EMA-EP (etoposide–platinum) or platinum-based regimens (TP/TE, BEP).
• Hysterectomy reduces tumour bulk and chemo cycles in older women who have completed childbearing, controls haemorrhage, and is primary therapy for PSTT/ETT.

Special tumours — PSTT and ETT

• Chemo-resistant; hysterectomy is the mainstay even when localised.
• For metastatic PSTT/ETT, platinum-based multi-agent chemotherapy is added, but prognosis is worse.
• Interval from antecedent pregnancy >48 months is the worst prognostic factor in PSTT.

High-yield: PSTT secretes human placental lactogen (hPL) and only modest hCG; it is chemo-resistant, so surgery (hysterectomy) — not EMA-CO — is the treatment of choice.

Post-treatment surveillance & contraception

• After hCG normalises, monitor monthly for 12 months (low-risk) — many centres now shorten low-risk follow-up; high-risk surveillance is more prolonged.
• Reliable contraception throughout follow-up — combined oral contraceptive pills (OCPs) are preferred. They do not increase the risk of post-molar GTN and prevent a new pregnancy from confusing hCG interpretation.
• Avoid IUCD until hCG is normal (risk of uterine perforation in an involuting/invaded uterus).
• Pregnancy is allowed only after 12 months of normal hCG; in any future pregnancy, obtain an early USG and check hCG 6 weeks postpartum (recurrence risk).

High-yield: OCPs are the contraception of choice during hCG surveillance and do not raise GTN risk; avoid the IUCD until hCG normalises.

Complications

• Haemorrhage — uterine, or torrential bleeding from vaginal metastases; intra-abdominal bleed from hepatic mets or uterine perforation by invasive mole.
• Respiratory failure / trophoblastic pulmonary embolism during evacuation of large molar/bulky disease.
• Metastatic complications — seizures/raised ICP from brain mets; hepatic rupture.
• Chemotherapy toxicity — myelosuppression, mucositis, alopecia; etoposide → secondary leukaemia (AML) and other second cancers with cumulative dose.
• Drug resistance / relapse — hence consolidation cycles and prolonged hCG surveillance.
• Reproductive: generally fertility is preserved with chemotherapy; slightly earlier menopause.

Key differentials

• Normal/multiple pregnancy & retained products — both raise hCG; resolve the diagnosis with USG and serial hCG trends.
• Ectopic pregnancy — abnormal hCG rise; absent intrauterine sac. Rarely a true ectopic molar/choriocarcinoma.
• Phantom hCG (heterophile antibody) — positive serum, negative urine hCG, no response to treatment.
• Pituitary hCG (perimenopausal LH cross-reactivity) — low-level hCG suppressible by oestrogen/OCP.
• Non-gestational choriocarcinoma (germ-cell tumour of ovary/testis/mediastinum) — choriocarcinoma arising without an antecedent pregnancy; behaves differently and is more chemo-resistant.
• Cervical carcinoma — important mimic of ETT (epithelioid trophoblast resembles squamous cell carcinoma on biopsy).

Recently asked / exam angle

• Single-best diagnosis vignette: plateauing hCG over 4 readings post-evacuation → "diagnosis = GTN" (apply the 4 FIGO criteria).
• Score → treatment mapping: a stem gives the eight WHO factors; you total them and decide ≤6 (single agent) vs ≥7 (EMA-CO). Memorise the cut-off 7.
• Full forms / components of EMA-CO are a recurring single-line MCQ.
• DOC for low-risk GTN = methotrexate (with folinic acid rescue); actinomycin-D when MTX contraindicated.
• PSTT/ETT "odd-one-out" questions: chemo-resistant, hPL-secreting, treated by hysterectomy — these break every rule and are favourite distractors.
• Most common metastatic site = lung; do not biopsy vaginal metastasis.
• Contraception of choice during follow-up = OCPs, avoid IUCD.
• Antecedent pregnancy of choriocarcinoma can be a normal term delivery — a classic trick.
• Phantom hCG identification (negative urine hCG) — increasingly tested as a clinical-reasoning item.

Rapid revision

1. GTN = malignant trophoblastic disease, trackable by beta-hCG; curable without tissue diagnosis.
2. Invasive mole = most common GTN; choriocarcinoma = most aggressive, earliest haematogenous spread.
3. Diagnosis (FIGO criteria): hCG plateau ×4 over 3 wk, rise >10% ×3 over 2 wk, persistence ≥6 mo, or choriocarcinoma histology.
4. WHO prognostic score: ≤6 = low risk → single agent; ≥7 = high risk → EMA-CO.
5. Low-risk DOC: methotrexate + folinic acid; alternative actinomycin-D.
6. High-risk regimen: EMA-CO = Etoposide, Methotrexate, Actinomycin-D / Cyclophosphamide, Oncovin (vincristine).
7. Metastatic order: Lung > Vagina > Brain/Liver; never biopsy a vaginal metastasis (bleeds).
8. PSTT & ETT arise from intermediate trophoblast, secrete hPL, are chemo-resistant → hysterectomy; not WHO-scored.
9. CXR counts lung metastases for the score (not CT micromets); CSF:serum hCG >1:60 = occult CNS disease.
10. Consolidation chemotherapy (2–3 cycles after hCG normalises) prevents relapse.
11. Contraception of choice = OCPs; avoid IUCD until hCG normal; conceive only after 12 months of normal hCG.
12. Phantom hCG: positive serum, negative urine hCG, no response — confirm by dilution before treating.