Gestational Trophoblastic Disease
Gestational trophoblastic disease is a group of uncommon conditions arising from the cells that would normally form the placenta. Rather than developing into a healthy pregnancy, these cells proliferate abnormally, producing a molar pregnancy in most cases and, less often, a malignant tumour. It is detected early in the great majority of cases, usually through a routine early pregnancy scan or because of bleeding, and the outlook is exceptionally good: even the malignant forms are among the most curable of all cancers, with cure achievable in nearly all cases including when the disease has spread. The condition produces the hormone hCG, which provides a uniquely sensitive way to monitor it, and this underpins the surveillance that follows treatment.
What is it?
When a pregnancy begins, the fertilised egg divides into two populations of cells. One becomes the embryo. The other, the trophoblast, becomes the placenta and the membranes, invading the uterine lining to establish the blood supply that will sustain the pregnancy. This invasive capacity is normal and essential, but it is tightly controlled.
Gestational trophoblastic disease arises when that control fails and trophoblast cells proliferate abnormally. The condition therefore always originates from a pregnancy event, which distinguishes it fundamentally from other gynaecological cancers and explains several of its unusual features—including the fact that the abnormal tissue is genetically distinct from the woman herself, containing paternal genetic material, which may contribute to why it responds so remarkably well to chemotherapy.
The spectrum divides into benign and malignant forms.
Hydatidiform mole, or molar pregnancy, is the benign and much more common end. It takes two forms distinguished by their genetics.
A complete mole arises when an egg that has lost its own genetic material is fertilised, usually by a single sperm that then duplicates. The resulting tissue therefore contains only paternal chromosomes. No embryo develops at all, and the placental tissue becomes a mass of fluid-filled swellings. This is the form classically described on ultrasound as resembling a bunch of grapes or a snowstorm.
A partial mole arises when a normal egg is fertilised by two sperm, producing an extra set of chromosomes. Some fetal tissue develops, often abnormally, alongside placental tissue that is partly cystic. The pregnancy is not viable.
The distinction matters because complete moles carry a substantially higher risk of persisting and requiring chemotherapy—around 15%—compared with a smaller proportion of partial moles.
The malignant forms are grouped as gestational trophoblastic neoplasia.
Invasive mole develops where molar tissue grows into the muscular wall of the uterus rather than remaining within the cavity, and is the most common form of persistent disease after a molar pregnancy.
Choriocarcinoma is a frankly malignant tumour that spreads through the bloodstream, with a particular tendency to reach the lungs, and less often the brain, liver, and elsewhere. It can follow a molar pregnancy, but importantly it can also follow a normal pregnancy, a miscarriage, or a termination—sometimes months or years later. This is why unexplained bleeding or unusual symptoms after any pregnancy event warrant a pregnancy test, since a positive result in that context is highly significant.
Placental site trophoblastic tumour and epithelioid trophoblastic tumour are rare variants arising from different trophoblast cell populations. They behave differently from the others: they produce relatively little hCG, so the usual monitoring is less reliable, and they respond less predictably to chemotherapy, so surgery plays a larger role.
The hormone hCG is central to this condition and deserves explanation. Trophoblast cells produce human chorionic gonadotrophin, the hormone detected by pregnancy tests. Because trophoblastic disease consists of these cells, it produces hCG in proportion to the amount of tissue present. This gives clinicians something rarely available in oncology: a precise, inexpensive blood test that reflects disease burden directly, detects persistence or recurrence long before any symptom or scan abnormality, and confirms cure when it falls to zero. The entire structure of follow-up and treatment decisions rests on this.
Very high hCG levels also explain several symptoms. The hormone structurally resembles thyroid-stimulating hormone, so extreme levels can overstimulate the thyroid, producing tremor, palpitations, and heat intolerance. High levels contribute to severe nausea and vomiting. They also stimulate the ovaries, producing large multi-cystic ovaries called theca lutein cysts, which resolve on their own after treatment.
Risk factors are relatively few. Age is the strongest, with risk rising substantially in women over 40 and also increased at the youngest extreme of reproductive age, reflecting a higher rate of the abnormal fertilisation events that cause the condition. A previous molar pregnancy increases risk considerably. Geographic and ethnic variation exists, with notably higher rates reported in parts of Asia, Africa, and Latin America, though how much of this reflects true difference versus reporting and dietary factors remains debated. Dietary factors including low carotene and animal fat intake have been implicated. Nothing a woman does during a pregnancy causes it, and this reassurance is worth stating explicitly.
The presentation has changed considerably. Historically, molar pregnancy presented later with a markedly enlarged uterus, heavy bleeding, passage of grape-like tissue, severe vomiting, and sometimes thyroid or pre-eclampsia features. Routine early ultrasound now identifies the majority before these develop, and many cases are found when a scan performed for bleeding or for dating shows an abnormal appearance, or when tissue from what appeared to be a miscarriage is examined.
Vaginal bleeding in early pregnancy remains the most common symptom. A uterus larger than expected for dates occurs in a proportion, though it may equally be normal or small. Severe nausea and vomiting beyond the usual range of early pregnancy is suggestive. Pre-eclampsia features before 20 weeks are unusual in any pregnancy and are a notable clue. Symptoms of an overactive thyroid occasionally occur.
Breathlessness or coughing up blood after a molar pregnancy may indicate spread to the lungs and requires urgent assessment, as does any neurological symptom.
Diagnosis combines ultrasound, hormone measurement, and tissue examination.
Pelvic ultrasound is the primary test. A complete mole typically produces a characteristic appearance of multiple small cystic spaces filling the uterine cavity with no fetus present. A partial mole shows fetal tissue alongside a thickened, cystic placenta. Early moles can be harder to recognise and are sometimes initially reported as a failed pregnancy, which is one reason tissue examination after any miscarriage or termination matters.
Blood hCG is measured and is often strikingly elevated in complete moles, frequently well above the level expected for gestational age.
Histological examination of evacuated tissue confirms the diagnosis and distinguishes the types. Where the distinction between a complete mole, a partial mole, and a non-molar miscarriage is unclear, genetic testing of the tissue resolves it, since the three have different chromosomal patterns.
Chest X-ray or CT assesses for lung involvement where persistent disease is suspected, and MRI of the brain and pelvis and CT of the abdomen are used in staging malignant disease.
Important to Know
This is one of the most treatable conditions in oncology, and that deserves stating plainly to anyone facing the diagnosis. Cure rates approach 100% for low-risk disease and exceed 90% even for high-risk disease that has spread, and fertility is preserved in the great majority. Care should be coordinated through a specialist trophoblastic disease centre, and in several countries including the United Kingdom this care is formally centralised with excellent results.
Treatment of a molar pregnancy is suction evacuation of the uterus, a short procedure under anaesthetic. Medical methods of evacuation are generally avoided for complete moles because of concerns about pushing tissue into the circulation, though practice varies. Hysterectomy is an option for women who have completed their families and reduces the risk of persistent disease, though it does not remove the need for monitoring entirely.
The part of care that matters most is what follows. Structured hCG surveillance monitors the hormone at defined intervals until it returns to normal and for a period afterwards. The duration depends on how quickly levels fall and on local protocols. This follow-up is what detects the minority who develop persistent disease, at a point when it is readily curable, and it is the reason outcomes in this condition are so good. Completing surveillance matters even when a woman feels entirely well—particularly so, since the whole purpose is detecting disease before it declares itself.
Contraception during surveillance is important, because a new pregnancy raises hCG and makes the results uninterpretable. Reliable contraception is advised for the duration of follow-up, and women are given specific guidance on when it is safe to conceive again. Hormonal contraception is generally considered safe once hCG has normalised.
Chemotherapy is given where hCG plateaus, rises, or fails to normalise within the expected period, or where there is evidence of spread. Treatment is guided by a risk score incorporating factors including age, the type of preceding pregnancy, the interval since it, hCG level, tumour size, sites and number of metastases, and any previous treatment. Low-risk disease is treated with single-agent chemotherapy, most often methotrexate, which is well tolerated and highly effective. High-risk disease is treated with combination chemotherapy. Even where initial treatment does not succeed, switching regimens usually achieves cure, which is unusual among cancers.
Fertility after treatment is preserved in the great majority of women. Most go on to have normal pregnancies, and chemotherapy for this condition does not meaningfully reduce the chance of future pregnancy for most women, though treatment at a young age with combination regimens can bring menopause forward slightly. Women are generally advised to wait until surveillance is complete before conceiving.
Future pregnancies carry a modestly increased risk of a further molar pregnancy—roughly 1 to 2 percent after one episode, higher after two. An early ultrasound in any subsequent pregnancy is recommended to confirm it is normal, and hCG testing some weeks after the end of any future pregnancy, however it concludes, is advised in many protocols to confirm it has returned to normal.
A specific and important point concerns pregnancy events after the diagnosis. Choriocarcinoma can follow any pregnancy, including a normal one, sometimes long afterwards. Unexplained bleeding, breathlessness, coughing blood, or neurological symptoms after any pregnancy, miscarriage, or termination warrant a pregnancy test, and a positive result in a woman who is not pregnant is highly significant and requires urgent assessment.
The emotional dimension deserves acknowledgement rather than being treated as secondary. A woman with a molar pregnancy has usually experienced a pregnancy loss, and is then told the tissue was abnormal, that she requires monitoring for cancer, and that she must postpone trying again. That combination—grief, fear, and delay—is genuinely difficult, and the medical reassurance about excellent cure rates does not address the loss itself. Support is available through specialist centres and patient organisations and is worth accessing.
A note about terminology is also warranted. Women frequently encounter the phrase “cancer” in connection with this condition and find it frightening. Most molar pregnancies are not cancer and never become cancer. The minority that persist are treated as cancer and are among the most curable forms that exist. Both facts are true and worth holding together.
Care is coordinated through specialist trophoblastic disease centres with gynaecology, medical oncology, and specialist nursing. hCG results, imaging, and clinical findings are interpreted together, with the hormone trend carrying the greatest weight.
Patient education plays an important role. Understanding that this condition arises from a pregnancy rather than from anything a woman did, that most molar pregnancies need no treatment beyond evacuation and monitoring, that completing hCG surveillance is the most important part of care, that contraception during that period is necessary for a practical reason, and that cure rates and future fertility are both excellent all contribute to appropriate care.
Red flag symptoms include heavy vaginal bleeding in early pregnancy, particularly with the passage of tissue or with dizziness and faintness; severe vomiting with inability to keep down fluids; breathlessness, chest pain, or coughing up blood, which may indicate spread to the lungs; severe headache, seizures, visual changes, or weakness, which may indicate spread to the brain; high blood pressure, severe headache, or visual disturbance before 20 weeks of pregnancy; symptoms of an overactive thyroid including tremor, palpitations, and marked heat intolerance; a rising or plateauing hCG level during surveillance; and any abnormal bleeding or unexplained symptom after a previous molar pregnancy. These warrant urgent medical assessment.