Predictors of Low Risk of Persistent Trophoblastic Disease in Molar Pregnancies
Isa Niemann, MD, Lone Kjeld Petersen, DM, Estrid S. Hansen, MD, and Lone Sunde, PhD
Source: From the Departments of Clinical Genetics, Gynecology and Obstetrics, and Pathology, University Hospital of Aarhus, Aarhus, Denmark.
OBJECTIVE: To search for predictive factors for low risk of persistent trophoblastic disease in patients with molar pregnancies.METHODS: A total of 270 consecutively collected, histologically confirmed hydatidiform moles were classified by ploidy using karyotyping and flow cytometry. The parental origin of the genome was determined by analysis of microsatellite polymorphisms. Data on clinical featuresand pathology reports were collected for each patient.
RESULTS: The observed frequency of persistent trophoblastic disease in patients with triploid moles was 0 of
105, (95% confidence interval 0–2.8%), whereas 28 of 162 patients with diploid molar pregnancies developed persistent trophoblastic disease (P < .001). Patients with a diploid mole and an initial hCG level lower than 49,000 units per liter did not develop persistent trophoblastic disease (P .03).CONCLUSION: The risk of persistent trophoblastic disease after a triploid mole is very low. By combining the present data with data from published studies with valid ploidy assessment, the frequency of persistent trophoblastic disease in patients with triploid moles is 0 of 196 (95% confidence interval 0–1.5%). We suggest that the surveillance program for patients with triploid molar pregnancies is shortened. Initial hCG less than 49,000 units per liter is a possible predictor of low risk of persistent trophoblastic disease in women with diploid molar pregnancies, but this observation needs confirmation in larger studies.
LEVEL OF EVIDENCE: II-2
In the majority of cases, hydatidiform mole resolves spontaneously, but approximately 10% of the patients
with molar pregnancies develop persistent trophoblastic disease and receive chemotherapy to obtain remission. To identify patients without spontaneous remission, all molar patients are surveyed with serial hCG
measurements after evacuation until 6–12 months after undetectable hCG levels have been reached.
Traditionally, a hydatidiform mole is classified as either a complete or a partial mole based on gross
morphology and histopathology.3,4 Complete moles most frequently have a diploid karyotype as opposed
to partial moles, which most often are triploid. Usually, diploid moles derive from fertilization of an
“empty” egg with either a haploid sperm (homozygosity) or by dispermy (heterozygosity).5,6 A minority
of diploid moles have biparental genomes. Triploid moles arise by dispermy and thus have 2 paternal sets
and 1 maternal set of chromosomes to the genome. Several attempts to describe risk factors for postmolar
persistent trophoblastic disease have been made. Persistent trophoblastic disease is mainly associated
with complete moles but has also been reported with partial moles.7,8 Some studies have shown
that patients with high maternal age, excessive uterine size, markedly elevated initial hCG, positive history
of hydatidiform mole, and marked trophoblastic proliferation have an increased risk of persistent trophoblastic
disease after a complete mole.9–12 Other studies, however, could not confirm these findings.13,14
In this study we took the complementary view: Can we find predictive factors to identify molar
patients without a risk of developing persistent trophoblastic disease? In an earlier study on 105 moles,
we found that of 42 women with triploid moles, none developed persistent trophoblastic disease.15 This
study extends our previous work.
MATERIALS AND METHODS
Fresh samples of evacuated tissue and 10 mL of heparinized blood were consecutively collected from patients with pregnancies clinically suspected of hydatidiform mole. When possible, a blood sample from
the father was also collected. The inclusion period went from April 1986 to June 2003. Thirteen gynecologic
wards, covering approximately 40% of the Danish population, participated in submitting the samples.
No patients contributed more than 1 sample. We received and inspected 387 samples with the
naked eye and under a dissection microscope (x25), finding 313 samples with vesicular villi (Ø 1 mm)
possibly representing hydatidiform mole. To diagnose molar pregnancy, 1 pathologist (E.S.H.) reviewed
the original slides using the criteria of Szulman and Surti4 without knowledge of the ploidy or primary histopathologic diagnosis. After the review, 270 conceptuses were diagnosed as hydatidiform moles. Of the 43 excluded samples, 14 could not be revised due to lack of original histopathologic material. We used karyotyping and flow cytometry to determine the ploidy of the molar tissue. Karyotyping was successful in 246 (91%) molar samples. Infection and formalin fixation were the main reasons for not obtaining metaphases. Eight moles were hypotriploid or hypertriploid, and 2 were hypodiploid or hyperdiploid and were classified as triploid or diploid, respectively. In 135 moles the DNA ploidy was determined by flow cytometry of unfixed interphase nuclei using the preparation techniques described by Vindelov16 with trout and chicken erythrocyte nuclei as controls. In 2 moles, the ploidy was determined by analysis of microsatellite polymorphisms.
The parental origin of the genome in the diploid moles was assessed by analysis of polymorphic DNA
markers. Standard techniques were used to isolate DNA from molar tissue and parental blood samples.
The analyses of DNA markers in the early part of the study have been described previously (Sunde L.
Genetic analyses of hydatidiform mole with conceptual and practical implications. PhD thesis, University
of Aarhus, Denmark 1990). In 109 diploid moles, DNA was amplified by polymerase chain reaction
using 10 primer pairs (D13S634, D13S305, D13S258, D18S51, D18S391, D18S978, D21S11, D21S141,
D21S1435, X22) flanking microsatellite loci with a heterozygosity frequency of 67–93%. The polymerase
chain reaction products were resolved by capillary electrophoresis with an ABI prism 310 Genetic Analyzer
(Applied Biosystems, Naerum, Denmark). The polymorphisms were analyzed using ABI prism GeneScan
software (Applied Biosystems). A mole was classified as androgenetic when the mole and the patient had no identical alleles in at least 2 loci. Androgenetic moles were classified as homozygous (P1P1) if all, and at least 4, successfully analyzed loci showed homozygosity. Androgenetic moles were classified as heterozygous (P1P2) when having a XY karyotype or when the mole was heterozygous in at least 1 locus or both. In 3 cases, maternal DNA was lacking and the moles were classified as androgenetic and homozygous, because they were homozygous in all of 10 loci. Data on clinical features and chemotherapy was collected from gynecologic and oncologic hospital records. All patients had at least 6 months of follow-up from evacuation date, and the median follow-up time was 10.4 years. We classified patients as having persistent trophoblastic disease if they were treated with chemotherapy. Methotrexate was the first choice of treatment to all patients. The Regional Committee on Biomedical Research Ethics of Aarhus County approved the project, and all patients gave informed consent. Logistic regression model, confidence intervals (assuming binomial distribution), and differences between groups (using the 2 test or Fisher exact test where appropriate) were analyzed with Stata 8.2 statistical software (StataCorp LP, College Station, TX).
RESULTS
We classified 162 moles as diploid, 105 as triploid, and 3 as tetraploid. Eight of the diploid moles were
part of twin pregnancies with a coexisting fetus.Twenty-eight patients were subsequently treated with
chemotherapy (Table 1). Seventeen patients were diagnosed with invasive mole, 2 with choriocarcinoma,
and 9 had persistently elevated serum hCG. Two of 8 twin pregnancies with diploid mole and a coexisting fetus were followed by persistent trophoblastic disease. Another 8 patients, 1 with a triploid and 7 with
diploid moles, had delayed normalization of hCG levels but were cured without chemotherapy. Five of
these achieved normal hCG values after a second evacuation. Three patients (with diploid moles) had
persistently low hCG values ( 60 units per liter) for 4, 12, and 23 months, reaching undetectable values
eventually. All of the 242 molar patients with spontaneous remission remained free of disease through the
follow-up period (6 months to 17 years). None of the patients with triploid or tetraploid molar pregnancies were treated with chemotherapy; 28 of 162 patients (17.3%) with a diploid mole developed persistent trophoblastic disease (P .001) The observed frequency of persistent trophoblastic disease after a triploid mole was 0 of 105, (95% confidence interval [CI] 0–2.8%).were excluded by the histopathologic review. Among these, 26 gestations were triploid. None of the 26 additional patients with triploid gestations developed persistent trophoblastic disease, and thus, 0 of 131 (95% CI 0–2.3%) patients with triploid gestations originally suspected of hydatidiform mole developed persistent trophoblastic disease (data not shown). Secondarily, we looked for factors that could point out patients with a low risk of persistent trophoblastic disease after a diploid mole. Table 2 gives the frequency of persistent trophoblastic disease after
diploid moles stratified by the parental origin of the molar genome. Among the 162 diploid moles, 149
(92.0%) were androgenetic and 12 were biparental. Of the androgenetic moles, 18 (12.1%) were heterozygous. In 1 mole the parental origin could not be determined. Although not significant, the frequency
of persistent trophoblastic disease was lower in patients with androgenetic, homozygous, or biparental
moles (16.7% and 16.8%) than in patients with androgenetic, heterozygous moles (22.2%). In Table 3,
maternal age less than 40 years, nonexcessive uterine size, initial hCG level less than 100,000 units per liter,
and parental origin of the genome were evaluated as predictors of low risk of persistent trophoblastic disease
among women with diploid moles. Using a multiple logistic regression model, none of the variables were predictors of spontaneous remission in diploid molar patients, although all parameters, though not significantly, reduced the risk of persistent trophoblastic disease. However, we did observe that none of 19 patients with an initial hCG level below 49,000 units per liter developed persistent trophoblastic disease (P .03).
DISCUSSION
This study aimed at identifying factors predicting a low risk of persistent trophoblastic disease after a
hydatidiform mole. As of now, all patients have serial hCG measurements after evacuation for a molar pregnancy, regardless of type. We observed no cases of persistent trophoblastic disease after 105 triploid moles. We could not identify predictors for low risk of persistent trophoblastic disease in women with diploid molar pregnancies, but in all of 19 patients with a diploid mole and an initial hCG level below 49,000 units per liter, spontaneous remission was observed (P .03). One problem in identifying predictive factors for
spontaneous remission is the identification of the group of patients with true gestational trophoblastic neoplasia. We defined patients with persistent trophoblastic disease as those who were given chemotherapy.
Our data were consecutively collected in a well-organized public health care system with reliable registration and central treatment of gestational trophoblastic disease. Because the frequency of persistent trophoblastic disease was as low as 17.3% among the patients with diploid moles, because all but 2 patients needed at least 3 courses of methotrexate to obtain remission, and because all of the patients in the nonpersistent trophoblastic disease group remained free of disease in the follow-up period, we believe that by far most of our patients with persistent trophoblastic disease truly had gestational trophoblastic neoplasia and that we did not overlook any case of gestational trophoblastic neoplasia. To secure the validity of the ploidy, we avoided flow cytometry on formalinfixed, paraffin-embedded tissue. Our observation of no cases of persistent trophoblastic disease after triploid moles substantiates those of Lawler et al17 and Ohama et al.18 These 2 studies were also based on consecutively collected samples and determination of ploidy by reliable genetic techniques. Combining our results with theirs, the observed frequency of persistent trophoblastic disease in
patients with triploid molar pregnancies adds to 0 of 196 (95% CI 0–1.5%). Cases of triploid mole succeeded by choriocarcinoma have been reported.19,20 This is expectable because choriocarcinoma can succeed every type of pregnancy. Thus, the confidence intervals for the risk of persistent trophoblastic disease after a triploid mole and after a normal pregnancy probably overlap. The risk of persistent trophoblastic disease after a triploid mole is very low and may even approach zero. We suggest that the surveillance program for patients with triploid molar pregnancies be shortened. An abbreviated follow-up period would imply less anxiety and shorter delay of child bearing for these women. To apply molar triploidy as a predictor of low risk of persistent trophoblastic disease, obtaining a valid ploidy is crucial. It is thus important to use
reliable techniques like karyotyping or flow cytometry on fresh tissue with 2 external controls.14,21 We secondarily evaluated possible predictors of spontaneous remission in women with diploid molar pregnancies. The observed frequency of persistent trophoblastic disease after a diploid mole was 17.3% in this study as in other studies.13,22–24 Wake et al25 observed that patients with androgenetic, homozygous moles less frequently required chemotherapy treatment (0%) compared with patients with androgenetic, heterozygous moles (60%). Studies by Lawler et al17 and Fisher and Lawler26 could not confirm that patients with androgenetic, heterozygous moles had a higher frequency of persistent trophoblastic disease. Likewise, we found no significant differences in the frequency of persistent trophoblastic disease in moles stratified by parental origin. Maternal age younger than 40 years, nonexcessive uterine size, and an initial hCG less than 100,000 units per liter reduced, however not significantly, the risk of persistent trophoblastic disease. With an initial hCG lower than 49,000 units per liter, though, we observed a significantly reduced frequency of persistent trophoblastic disease (P .03). Two studies report that women reaching a serum hCG value less than 50 units per liter or a urinary hCG less than 40 units per liter within 4 to 8 weeks after the first evacuation have a low risk of persistent trophoblastic disease.27,28 A prompt predictor of low risk of persistent trophoblastic disease would be of greater benefit to the patients. Low initial hCG is a potential predictor of spontaneous remission in women with diploid moles, but the best estimate of a cutoff level and its clinical applicability need to be studied in larger studies. Triploid hydatidiform moles carry a very low risk of persistent trophoblastic disease. Further studies of low risk factors, such as low initial se-hCG, for diploid
molar pregnancies are important. Our observations furthermore imply that diploid and triploid moles possibly represent 2 different biologic entities with different clinical properties.
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