Describe the antecedents, features, staging and management of gestational Trophoblastic Neoplasia.

Highly chemosensitive — curable even with metastases.

Definition

Gestational trophoblastic neoplasia (GTN) is the malignant form of gestational trophoblastic disease, comprising invasive mole, choriocarcinoma and placental-site trophoblastic tumour. Choriocarcinoma is a highly malignant tumour of the trophoblast that invades and metastasises early via the blood-stream.

Gestational Trophoblastic Disease Spectrum

Antecedent Pregnancy

GTN follows a hydatidiform mole in ~50% of cases, an abortion/ectopic in ~25%, and a normal term pregnancy in ~25%. Post-molar GTN is diagnosed when the β-hCG plateaus or rises over consecutive weeks after evacuation.

Pathology

Choriocarcinoma is a soft, purple, haemorrhagic and necrotic tumour composed of sheets of malignant cyto- and syncytio-trophoblast with no chorionic villi; it invades the myometrium and blood vessels early, which explains its rapid haematogenous spread. An invasive mole, by contrast, retains hydropic villi that penetrate the myometrium. Bilateral theca-lutein cysts may persist owing to the high β-hCG.

Clinical Features

Persistent or irregular vaginal bleeding after a molar pregnancy, abortion or delivery, with subinvolution of the uterus and a rising/plateauing β-hCG. Because spread is haematogenous, women may present with features of metastases — lung (commonest — haemoptysis, dyspnoea), vagina (a bluish nodule that bleeds), brain (neurological deficit) and liver.

Investigations

• Serial β-hCG — the tumour marker for diagnosis, monitoring and follow-up.
• Ultrasound of the uterus/pelvis (Doppler shows vascular invasion).
• Metastatic work-up — chest radiograph/CT, CT/MRI brain, and liver imaging.

Staging and Risk Scoring

Staged by the FIGO anatomical stages I–IV and risk-stratified by the WHO/FIGO prognostic scoring system (age, antecedent pregnancy, interval, hCG level, tumour size, site and number of metastases, and prior chemotherapy): a score of ≤ 6 is low-risk and ≥ 7 is high-risk, which determines therapy.

Management

• GTN is highly chemosensitive and chemotherapy is the mainstay.
• Low-risk disease — single-agent chemotherapy (methotrexate with folinic-acid rescue, or actinomycin-D).
• High-risk disease — multi-agent chemotherapy (EMA-CO regimen), with surgery/radiotherapy for selected sites (e.g. Brain metastases).
• Follow-up with serial β-hCG until normal for a defined period, and reliable contraception during treatment and follow-up.

WHY Β-HCG Makes GTN a Uniquely Manageable Cancer

The extraordinary feature of gestational trophoblastic neoplasia is why it is one of the most curable of all malignancies — even when widely metastatic. Two properties account for this. First, it possesses a near-perfect tumour marker: the trophoblast secretes β-hCG in direct proportion to the number of viable tumour cells, and this can be measured in the blood with great sensitivity. This means the disease can be diagnosed early (by a plateauing or rising β-hCG during follow-up after a molar pregnancy), its response to treatment monitored precisely (a falling titre proves the chemotherapy is working), its complete eradication confirmed (a normal titre), and its recurrence detected before any clinical sign — a degree of biological surveillance available in almost no other cancer, and the reason that the follow-up of every hydatidiform mole is by serial β-hCG. Second, the tumour is exquisitely sensitive to chemotherapy (methotrexate in low-risk disease; multi-agent EMA-CO in high-risk). Together these give cure rates approaching 100% in low-risk and above 90% in high-risk disease, with fertility usually preserved. Understanding that a measurable marker plus a chemosensitive tumour equals cure explains the whole approach to this disease.

WHY Every Mole Must Be Followed Up — and Contraception Is Mandatory

A rule of absolute importance is why a woman whose hydatidiform mole has been evacuated is not discharged, but followed with serial β-hCG — and why she must not conceive during that period. After evacuation, a proportion of moles (about 15–20% of complete moles) do not resolve but persist as invasive mole or progress to choriocarcinoma — and this can only be detected by watching the β-hCG: it should fall progressively to normal; a plateau or a rise signals persistent trophoblastic disease and the need for chemotherapy. This surveillance is the whole reason such women survive. But it depends entirely on the β-hCG being interpretable — and a new pregnancy also produces β-hCG, which would completely obscure the signal, making it impossible to tell a normal pregnancy from a growing malignancy. This is why effective contraception is mandatory throughout the follow-up period (the combined oral pill is suitable; an IUCD is avoided until the β-hCG is normal, because of the risk of uterine perforation). Understanding that follow-up is a chemical watch that pregnancy would blind explains why contraception is not advice but a requirement.

• GTN includes invasive mole, choriocarcinoma, placental-site trophoblastic tumour and epithelioid trophoblastic tumour; it follows a molar pregnancy (~50%), abortion or a normal pregnancy.
• Choriocarcinoma spreads early and haematogenously — the lungs are the commonest site (also vagina, brain, liver).
• β-hCG is a near-perfect tumour marker — used for diagnosis, monitoring response, confirming cure and detecting recurrence.
• Treatment: single-agent methotrexate (low-risk, WHO score ≤6) or multi-agent EMA-CO (high-risk) — cure rates approach 100% (low-risk) and >90% (high-risk), with fertility preserved.
• Every mole needs serial β-hCG follow-up with mandatory contraception (a new pregnancy would obscure the marker).