Advances in diagnostics and management of gestational trophoblastic disease

HM can be classified as a complete hydatidiform mole (CHM) or partial hydatidiform mole (PHM) based on histopathological exam and genetics.⁸ The common pathology of these lesions is excessive proliferation of trophoblast.⁶ In both conditions, the placental villi become oedematous, forming hydatidiform structures.⁷ In CHM hydrops is fully developed and most villi are involved. In PHM however, the hydrops remains characteristically focal.⁶ In CHM foetal parts are absent.⁹ In PHM evidence of foetal development, such as amnion vessels with foetal red blood cells, is a prominent pathologic feature.⁷ HMs are genetically characterised with two copies of the paternal genome. Typical CHMs are diploid and androgenetic with both sets of chromosomes derived from the paternal genome and no contribution to the nuclear genome from the mother.⁸ The monospermic 46, XX karyotype is most common, resulting from fertilisation of an ovum by a single sperm that then duplicates its DNA.^8,10 About 10% of CHMs are 46, XY, arising by dispermy. 46, YY embryos are presumed to be non-viable.⁸ PHMs are almost always triploid, having an additional set of chromosomes from the father of the embryo. Most have a 69, XXX or 69, XXY karyotype usually resulting from fertilisation of an ovum by two sperms, or less frequently a diploid sperm.^7,8 Trisomy with XYY karyotype is rarely seen and YYY karyotype has not been observed.⁷ Most molar pregnancies are sporadic. A small subset of women has an inherited predisposition to recurrent molar pregnancies, referred to as familiar recurrent hydatidiform mole (FRHM).^8,9

The diagnosis of HM is usually suspected on ultrasound imaging. Clinical signs, symptoms, and human chorionic gonadotropin (hCG) levels can be helpful in the diagnostic process.¹¹ Diagnosis should always be confirmed by histology with or without ancillary techniques such as genotyping and p57kip2 staining.¹²

Most GTDs secrete hCG which is therefore a sensitive tumour marker.¹ HCG is a glycoprotein hormone produced by trophoblastic tissue. It comprises an α and a β subunit. The α subunit is shared with other members of the glycoprotein hormones, including thyroid-stimulating hormone (TSH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In hCG, the α subunit can mimic the α subunit of the other glycoprotein hormones and therefore cause symptoms seen in hyperthyroidism.^1,10 The β subunit is a unique part of the hCG structure that allows the production of highly specific antibodies and the utilisation of highly specific immunologic assays.²¹ In a healthy pregnancy, intact hCG is the predominant protein, whereas in cancer patients various hCG isoforms can be present. These include intact hCG (α & β), the partially degraded or nicked forms of hCG (hCGn) and hCGβ (hCGβn) and the β-core fragment (hCG βcf)).²² The combination of US findings with elevation of hCG above expected for gestational age is highly suggestive of molar pregnancy⁷ and is crucial in diagnosis of GTD or GTN.¹ Due to hyperplastic trophoblastic cells in CHM, patients will have marked elevations in hCG, sometimes greater than 100.000 IU/L. However, such elevations are seen in fewer than 10% of patients with PHM.¹¹

HM is sometimes diagnosed only by pathology after suction dilation and curettage (D&C) is performed for a suspected early embryonic demise. When HM is suspected beforehand, it should be evacuated as soon as possible.⁷ Histological confirmation of GTD after evacuation is mandatory.¹²

The initial treatment of HM in women who wish to preserve fertility is D&C.²³ Pre-treatment evaluation consists of measurement of serum quantitative beta-hCG, complete blood count, clotting studies (PT, PTT), renal and liver functions, blood type and screen, pelvic ultrasound examination, chest X-ray and thyroid function test if hyperthyroidism is suspected.⁷ Where available, D&C is performed under ultrasound guidance which helps to remove all molar tissue and avoid uterine perforation.^11,24 Usually, it is performed under general anaesthesia.⁷ Intravenous oxytocin infusion may be started at the onset of suction D&C and may be continued for several hours after operation. Oxytocin enhances uterine contractility and decreases blood loss.²⁴ There is theoretical concern over the routine use of oxytocic agents, because of the potential to embolise and disseminate trophoblastic tissue through the venous system.²⁵ However, the authors recommend the use of oxytocin in management of molar pregnancy.^2,7,24 The risk of bleeding after suction D&C increases with uterine size. When the uterus is greater than 16 weeks in gestational size, blood transfusion should be available.²⁴ Because RhD factor is expressed on trophoblastic tissue, RhD immunoglobulin should be administered at the time of uterine evacuation in Rh negative women. If HM is diagnosed at early gestational age, complications during or after evacuation are uncommon.²⁶ Most common complications are excessive bleeding, uterine perforation, and respiratory distress syndrome.²⁷ Respiratory distress syndrome may be caused by trophoblastic embolization, high-output congestive heart failure caused by anaemia, hyperthyroidism, preeclampsia, or iatrogenic fluid overload.⁷ At the end of suction D&C, the evacuated tissues should be inspected and sent for histological examination.²⁷ Uterine evacuation by medication only method is not recommended due to high failure rates, risk of haemorrhage, increased risk of post-molar GTN and increased maternal morbidity.^7,23

Hysterectomy with salpingectomy is an alternative method to suction D&C if molar pregnancy is presumed and childbearing is complete.^24,28 Hysterectomy is especially used in women older than 40 years, because these patients have a higher risk of post molar GTN. Hysterectomy eliminates the possibility of local myometrial invasion as a source of persistent disease and hence reduces the need for subsequent chemotherapy.^7,27,28 Usually the adnexa may be preserved, even if theca lutein cysts are present. Theca lutein cysts usually regress over few months after uterine evacuation as hCG levels decrease.^7,27 Hysterectomy, compared to uterine evacuation, has a significant advantage in preventing post-molar GTN with an approximately 80% reduction in risk.^26,28 Because hysterectomy does not eliminate the possibility of post molar gestational trophoblastic neoplasia these patients should also be monitored postoperatively with serial hCG measurements.⁷

Prophylactic administration of either methotrexate or actinomycin D chemotherapy at the time of or immediately following molar evacuation is associated with a reduction in the incidence of post molar GTN to 3%-8%. However, it should be limited to special situations where adequate hCG follow-up is not possible and the risk of post molar GTN is much greater than normal.²⁴

The gold standard for clinical management of women diagnosed with a HM is to monitor the hCG levels in urine or serum.²² Following evacuation of molar pregnancy, monitoring of hCG levels postoperatively is mandatory to identify and manage post-molar GTN.²⁷ HCG is used as a marker in post molar monitoring because of the correlation between hCG levels and trophoblastic tumour burden, allowing early diagnosis and treatment of GTN.²⁹ The mean time to hCG normalization in case of partial HM is 6 weeks and in case of complete HM 7 weeks. For both complete and partial HM, 95% of patients reached normal serum hCG concentrations within 14 weeks after evacuation.³⁰ FIGO recommends hCG monitoring every 1-2 weeks until hCG is normalised, and then on monthly intervals. For PHM, one additional confirmatory normal hCG measurement 1 month after first hCG normalisation is recommended. For CHM, monthly hCG measurements are required for 6 months after hCG normalisation.^27,31 After evacuation of a HM effective contraception is crucial because a new pregnancy may confound the interpretation of hCG levels.²⁹

GTN has a varying presentation depending on the antecedent pregnancy event, disease type and extent. Post molar GTN can be associated with irregular bleeding after initial treatment for molar pregnancy, an enlarged and irregular uterus, and bilateral ovarian enlargement. However, these signs may be absent.¹¹ Patients often present with symptoms of metastatic disease. The most common metastatic sites are the lungs, but metastatic lesions can also be found in vagina, liver, brain, spleen, kidneys, and bowel. Characteristically, gestational choriocarcinoma forms a rapidly growing tumour with the ability to metastasize to virtually every body site and present with widespread dissemination. Metastatic lesions often produce abnormal bleeding because trophoblastic tumours have fragile vessels.^9,11 Embolization of trophoblastic tissue is also possible, and it can cause dyspnoea, coughing, chest pain, tachypnoea, and haemoptysis. Vaginal metastases can present with bleeding, which cannot be distinguished from the uterine blood loss. A gynaecological examination upon presentation is therefore important.¹ Liver metastases are rare and often have a poor prognosis, especially if they present with intra-abdominal bleeding, which is life-threatening. Central nervous system lesions may be asymptomatic or produce subtle neurologic symptoms such as headache. Symptoms from brain metastases can also be very severe, even fatal if they cause intracranial haemorrhage.^1,7 PSTT and ETT often present with irregular bleeding after some time has passed from a previous pregnancy and there may also be signs of metastatic disease.¹¹ Other rare symptoms such as virilisation and nephrotic syndrome have also been described.³⁴

GTN is most frequently diagnosed based on hCG values as discussed above, most often without histologic verification.⁷ It is essential to measure hCG in any woman of childbearing age who has unexplained metastatic disease.³⁶ A serum hCG determination and exclusion of normal pregnancy is essential to diagnose GTN in these circumstances, which can spare the patient an unnecessary surgery to establish the diagnosis.⁷

When a GTN diagnosis is made or suspected, immediate evaluation for metastases is needed. Along with the history and physical examination, the following evaluation should be performed: complete blood count, clotting function studies, renal and liver function studies, blood type and determination of pre-treatment hCG concentration.^7,37 A gynaecological examination should be done to exclude vaginal or pelvic metastases. Biopsy of metastatic lesions without the ability to control bleeding is highly risky due to abundant vascularisation of this type of tumours and is not essential before starting chemotherapy.^11,36 However, where complete excision is possible, histologic confirmation of the diagnosis is also valuable.³⁶

Extensive radiographic evaluation should be performed. Chest X-ray is appropriate to diagnose lung metastases and can be used for counting the number of lung metastases to evaluate the risk score. Lung CT may not be used in the risk score. Liver metastases may be diagnosed by US or CT. Brain metastases may be diagnosed by MRI or CT.^11,24

To categorise patients with GTN, two different systems can be used. They both correlate with clinical outcomes and identify patients at risk for failure of treatment.⁷ Currently, the 2000 FIGO staging system is the standard classification (Table 2).

Patients are also assigned a modified World Health Organisation (WHO) prognostic index score based on prognostic factors modified as FIGO score (Table 3). It comprises age, antecedent pregnancy, interval from index pregnancy (in months), pre-treatment hCG (in mIU/mL), largest tumour size including uterus (in cm), site of metastases including uterus, number of metastases identified and previous failed chemotherapy.²⁴ A WHO risk score of 6 or lower is classified as lowrisk and scores higher than 6 are classified as highrisk.^7,24 Staging notation uses a Roman numeral indicating FIGO anatomical staging followed by an Arabic numeral that represents WHO prognostic scoring.³⁷ FIGO risk scoring is not recommended in PSTT and ETT, although it may be of value in guiding management.³⁵

Low-risk GTN (FIGO/WHO score 0–6) is primarily treated with one of two single-agent drugs, methotrexate (MTX) or actinomycin-D (Act-D). A variety of doses and infusion schedules for these drugs have been utilized.^24,26 To date, there is not a clearly superior regimen between these two drugs. Treatment therefore is often determined by institutional preference.²⁶ In Europe and North America, the methotrexate with folinic acid (MTX-FA) 8-day and MTX 5-day regimens are favoured over Act-D as first-line treatment.³⁸ Single-agent chemotherapy induces complete remission in 83.5% patients with stage I GTN, 80% patients with low risk stage II GTN and 81.8% patients with low risk stage III GTN.³⁹ Chemotherapy response is monitored by hCG measurements at least every 1 or 2 weeks. Chemotherapy resistance is indicated by plateau in hCG over 3 consecutive cycles or a rise in hCG over 2 consecutive cycles.¹¹ Approximately 25–30% of low-risk patients develop resistance or excessive toxicity to initial single-agent chemotherapy.³⁸ Resistance to initial single-agent chemotherapy is up to 70–80% in patients with FIGO/WHO score 5 or 6. Current challenge is whether these patients should be still considered low risk and initially treated with single-agent chemotherapy or treated with more intensive therapy from the onset.^38,40 Low-risk patients experiencing treatment failure with one single agent are treated with other.⁴¹ Patients with low-risk GTN resistant to either single-agent chemotherapy or relapsed disease following complete response to initial single-agent chemotherapy, are treated with multi-agent chemotherapy. Most commonly with EMA-CO regimen (etoposide, methotrexate, actinomycin D, cyclophosphamide, vincristine).^38,41 Multi-agent chemotherapy is associated with increased short-and longer-term toxicities. For this reason, promising new strategies are being investigated. For example, the use of carboplatin and immunotherapy agents (programmed death protein 1 (PD-1) inhibitors and programmed death ligand 1 (PD-L1) inhibitors).^{38,42, 43, 44} In women who no longer wish to retain their fertility, first-line hysterectomy can be considered as an alternative to chemotherapy for treatment of low-risk non-metastatic GTN.²⁷ Once hCG has normalised treatment is continued for a minimum of four weeks, which represents at least two consolidation cycles.^12,38

High-risk GTN (FIGO/WHO score > 6) is treated with multi-agent chemotherapy, with or without adjuvant surgery or radiotherapy. The most used chemotherapy protocol is EMA-CO.²⁴ In EMA-CO failures, the most employed regimen is EMA-EP (substituting etoposide and cisplatin for cyclophosphamide and vincristine in the EMA-CO regimen).²⁶ In high-risk GTN patients EMA-CO regimen induces complete response at rates of 71-78% and long-term survival rates of 85-94%.⁴⁵ Unlike for patients with low-risk GTN, primary hysterectomy is not effective in reducing requirement for chemotherapy or improving cure rates in patients with high-risk GTN.²⁷ As with low-risk disease, chemotherapy for high-risk disease is continued for at least 2 to 3 consolidation courses after the first hCG normalization.^11,41 A separate category of ultra-high-risk GTN, defined as WHO score 13 or more, identifies women at high risk of early death and poor outcome.^26,41 These patients are treated with low dose induction chemotherapy before initiating multi-agent chemotherapy. Induction chemotherapy reduces the risk of life-threatening complications, predominantly haemorrhage from metastatic implants.²⁶ For induction chemotherapy combination of low dose etoposide (100 mg/ m²) and cisplatin (20 mg/m²) (EP on days 1 and 2 every 7 day, one to three cycles) is used.^26,40 Active areas of investigation include the utilization of high-dose chemotherapy with stem cell support, use of immunotherapy and other chemotherapy regimens.^11,26

Treatment of PSTT and ETT is determined by two independent poor prognostic factors: an interval of ≥48 months from the causative pregnancy and stage IV disease. Stage I tumours (confined to the uterus) arising <48 months since the antecedent pregnancy are treated with a total abdominal hysterectomy including removal of any suspicious pelvic and retroperitoneal lymph nodes. Adjuvant systemic therapy is not required. In contrast, if the PSTT/ETT originated from a pregnancy > 48 months previously, then such stage I patients and stage II–IV patients should be offered aggressive platinum-based chemotherapy including the option for experimental treatments such as high-dose chemotherapy or immunotherapy.⁴¹ Residual masses after treatment should be excised wherever possible to confirm no active cancer remains.^35,41 The survival rate is approximately 100% for non-metastatic disease and 50-60% for metastatic disease.⁴⁵

Research in GTD is mainly focused on the development of new treatment strategies (Table 4). Especially, finding alternatives to multi-agent chemotherapy and associated short- and longer-term toxicities.³⁸ The use of immunotherapy is an important development in the management of GTN, particularly in drug-resistant disease.⁴⁴ The programmed cell death ligand 1 (PD-L1) is expressed in all pre-malignant and malignant GTD and anti-PD-1 monoclonal antibodies, such as pembrolizumab, are becoming important part of the management of relapsed chemo-resistant GTB.^38,41,44 The use of immunotherapy must be further evaluated, particularly because of the high cost and lack of longer-term safety data.³⁸

Remission of GTN is defined as three consecutives normal hCG (hCG normalisation).²⁶ Posttreatment surveillance for low and high-risk GTN consists of weekly hCG measurements for 6 weeks after normalisation, then monthly for at least 12 months.^24,41,42 Surveillance for ultra-high-risk GTN is longer and consists of monthly hCG measurements for 24 months after completion of consolidation chemotherapy.²⁶ A minimum of 5-year-follow-up is advised.¹² Rising serum hCG in not sensitive for identifying recurrence of PSTT and ETT. Therefore, in cases of PSTT and ETT surveillance with 6 monthly MRIs is recommended.²⁶ Throughout surveillance period, patients must use reliable contraception because a new pregnancy may confound the interpretation of hCG levels [24]. Because of the 1–2% risk for a second mole in subsequent pregnancy, early ultrasound examination is recommended during all future pregnancies in addition to histologic evaluation of the placenta, and postdelivery hCG.⁷

There is a need for possible future investigations to identify factors, predicting which molar pregnancies will resolve spontaneously, persist as GTN or transform into choriocarcinoma, PSTT or ETT.²⁵

It has become evident, a redefinition of the FIGO/WHO scoring system to predict resistance to single-agent chemotherapy, is needed. With an “intermediate” risk group patients scoring WHO 5 and 6 can be identified for more intensive multi-agent chemotherapy from the outset.^25,38

Although medical outcomes of GTD have been widely explored, limited data are available regarding the related psychological, sexual and fertility issues.⁴⁶ Improved understanding of the impact of GTD on women and their families, and how they may suffer is warranted.²⁵