1 Medical Department, Gynecological Unit, 2 Clinical Biological Department and 3 Surgical Department, Institut Gustave-Roussy, 94805 Villejuif and 4 Molecular Biology and Hormonology Department, Hôpital Bicêtre, 94275 Le Kremlin-Bicêtre Cedex, France
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Abstract |
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Key words: human chorionic gonadotrophin/inhibin/marker/trophoblastic disease
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Introduction |
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Inhibins are also produced by the placenta and fetal membranes during pregnancy (Riley et al., 1996, 2000
; Fowler et al., 1998
; Petraglia et al., 1999
). Indeed, human placentas express inhibin ß- and
-subunit transcripts and proteins (Petraglia et al., 1991
; McCluggage et al., 1998
). Inhibins may be important regulators of fetal and placental development as well as being involved in the establishment of pregnancy (Riley et al., 1996
). This probably explains why serum maternal concentrations vary according to the term of the pregnancy, declining after delivery (Wallace et al., 1997
). Measurement of serum inhibin is useful in cases of various gestational pathologies, including pre-eclampsia, Down's syndrome and molar pregnancies (Aitken et al., 1996
; Muttukrishna et al., 1997
). Inhibin has been also postulated to play a role in trophoblastic molar invasion and its presence in molar trophoblast cells has been reported (Minami et al., 1993
; McCluggage et al., 1998
; Pelkey et al., 1999
; Shih and Kurman, 1999
). However, controversies exist regarding the clinical interest of measuring inhibin in patients bearing trophoblastic tumours (Yohkaichiya et al., 1989
; Badonnel et al., 1994
). This is due to the fact that immunoassays used in these studies detect total inhibin without differentiating the two molecular forms.
Taking advantage of the recent development of specific immunoassays for inhibin A and inhibin B (Robertson et al., 1996), we investigated whether molecular forms of inhibin may represent better markers than human chorionic gonadotrophin (HCG) and its free ß subunit (HCGß) for diagnosis, prognosis and follow-up of gestational trophoblastic diseases (GTD). Indeed, if HCG and HCGß are well-established sensitive markers of GTD (Schlaerth et al., 1981
; Fan et al., 1987
; Yedema et al., 1993
), they have no predictive value either for prognosis or for response to chemotherapy and, moreover, their normalization after evacuation is variable over time (Bagshawe et al., 1976; Azab et al., 1988
; Bidart et al., 1999
).
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Materials and methods |
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Chemotherapy consisted of a combination of dactinomycin and etoposide every week for the treatment of hydatidiform and invasive mole, and a combination of dactinomycin and etoposide every 2 weeks plus cisplatin every 4 weeks for choriocarcinoma and for methotrexate-resistant hydatidiform mole.
Serum inhibins A and B were measured using a two-site (sandwich) enzyme-linked immunoassay (ELISA; Serotec, Oxford, UK). These tests are based on specific monoclonal antibodies raised against the , ßA and ßB subunits. Briefly, each assay was performed as follows: serum samples were first mixed with a 10% sodium dodecyl sulphate solution and incubated at 100°C for 3 min. After cooling, a hydrogen peroxide solution was added to tubes for a further incubation at room temperature. Samples were then transferred to antibody-coated microtitre plates and incubated at room temperature for 2 h (for inhibin A) and overnight (for inhibin B), according to the manufacturer's instructions. Recombinant inhibin A and inhibin B were used as standards. The inhibin A and B detection limits were 4 and 10 ng/l respectively. Serum HCG and free HCGß were measured using specific immunoradiometric assays (Cisbio International, Giff sur Yvette, France) (Ozturk et al., 1987
). The intra- and interassay coefficients of variation were <4% and <7% for inhibin A, and <4% and <8% for inhibin B respectively.
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Results |
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Discussion |
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Our present observations demonstrate that the specific measurements of serum molecular forms of inhibins, namely inhibins A and B, do not seem to be of any clinical relevance in the biological survey of patients with GTD. Indeed, all our patients had elevated serum HCG and HCGß concentrations, while only 15 had elevated inhibin A, including only two patients with choriocarcinoma, and seven had a moderate increase of inhibin B, indicating that inhibins A and B are not sensitive enough markers. As is the case during pregnancy, inhibin A appears to be the major circulating form (Wallace and Healy, 1996). Although no serum measurement was performed before evacuation, all the patients included in our study had persistent or recurrent GTD. Moreover, three patients had choriocarcinoma, which is known to be a more aggressive disease.
In ten patients, serial determinations were performed during chemotherapy. Inhibin A was elevated in eight of these and a correlation was found between the kinetics of inhibin A and those of HCG and HCGß. However, the time to normalization was similar for the three parameters, except for five patients in whom it was faster for inhibin A. No correlation between inhibin B, HCG and HCGß was found. There was no benefit for inhibin determination before and during chemotherapy for GTD. A correlation was found between the kinetics of inhibin A and HCG during normal pregnancy: there was a peak at 910 weeks, coinciding with the HCG peak, and then a fall to a plateau between 1530 weeks.
Yohkaichiya and collaborators reported the evolution of total inhibin, HCG and FSH serum concentrations before and 710 days after mole evacuation in six patients bearing hydatidiform mole (Yohkaichiya et al., 1989). Before evacuation, serum inhibins were higher than those observed during normal pregnancies at the same term. Three patients had elevated inhibin concentrations higher than those seen in the follicular phase of normal menstrual cycles 2 weeks after evacuation. Only the latter developed a persistent trophoblastic disease. But in one case, inhibin concentrations were at the upper limit of normality, which was then considered to be elevated. So, we may conclude that in this study, inhibin failed to detect a persistent disease (Wallace and Healy, 1996
).
In conclusion, inhibin A and B do not seem to be reliable markers for persistent GTD. HCG and its free HCGß remain the most efficient and useful tumour markers for the diagnosis and follow-up after treatment of GTD.
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Acknowledgements |
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Notes |
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References |
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Submitted on February 27, 2001; accepted on August 13, 2001.