Section 5 -

Diagnostic Pitfalls of Molar Lesions Michael Wells Academic Unit of Pathology, University of Sheffield Medical School Sheffield , S10 2RX , UNITED KINDOM

Introduction An excellent review of the pathology of molar disease has recently been published [1]. This handout will focus on recent developments over the last 5 years. Hydatidiform mole is characterized by: hydropic change cistern formation excessive trophoblast abnormal distribution of trophoblast trophoblastic inclusions Complete mole: 46XX, paternal haploid sperm fertilizes empty ovum & undergoes cytogenesis diploid sperm fertilizes empty ovum all chorionic villi affected pleomorphism of trophoblast absence of fibrosis Partial mole [2]: triploid; 69,XXY 69,XXX or 69,XYY defective zona pellucidum dispermic fertilization of haploid ovum fetal parts may be present two populations of villi enlarged villi (>or= 3-4mm) with central cavitation irregular (angulated) profile of villi with trophoblast inclusions excess trophoblast may be subtle abnormal (angioectatic) vasculature in second trimester Pathological mimics of partial mole [2]: Beckwith-Wiedemann syndrome Placental angiomatous malformation Twin gestation with complete mole and existing fetus (see below) Early complete mole (see below) Hydropic spontaneous miscarriage Discordance in histopathological diagnosis is frequently seen in partial mole versus hydropic miscarriage and results from difficulty in evaluating trophoblastic hyperplasia. Ploidy analysis can improve concordance [3](see below). Early complete mole In the 1960s the mean age at evacuation of hydatidiform mole was 17 weeks. Nowadays, with the introduction of ultrasound examination as part of the routine clinical management of early pregnancy complications, it is 9.4 weeks and before the classical clinical or pathological features have developed. Thus, the histological features of complete hydatidiform mole are more subtle [4]. A common error made by histopathologists in molar disease is the erroneous diagnosis of early complete hydatidiform mole as partial mole. Non-triploid partial moles probably do not exist [5]. Certain typical features are seen only in early complete mole: abnormally shaped villi –branching or polypoid stromal mucin stromal vessels may be present STROMAL NUCLEAR DEBRIS We have recently shown (unpublished data) that the stromal debris which is a feature of early complete mole is the result of increased stromal proliferation and apoptosis, a finding also recently demonstrated by Kim et al [6]. Ki-67 index & p53 of villous stroma (unpublished data) DIAGNOSIS MEAN N Std deviation Early complete mole 22.31 18.71 30 5.75 7.18 Partial mole 8.33 5.26 22 5.66 2.86 Hydropic miscarriage 5.19 3.07 18 4.28 2.88 P<0.05 There is a statistically significant strong positive correlation between Ki67 proliferation index and p53 expression (rho=0.840; p<0.05). Ki67 proliferation index and p53 expression of villous stromal cells are strongly correlated with the amount of stromal karyorrhetic debris (rho=0.791; p<0.05). Kim et al suggest that complete vasculogenic differentiation is significantly retarded in early complete mole, due to increased apoptosis in the precursor components of blood vessels [6]. Ploidy analysis and p57kip2 Ploidy analysis is of great value in making the distinction between a diploid complete mole and a triploid partial mole. It may also aid the distinction between a diploid hydropic miscarriage and a triploid partial mole [3]. This may be achieved by flow cytometry or digital image analysis. In my own laboratory we have moved exclusively to digital image analysis. However, the greatest recent advance in the histopathology of molar pregnancy has been the introduction of immunohistochemistry for p57kip2 [7, 8, 9]. P57kip2 paternally imprinted gene, 11p15.5 maternally expressed villous cytotrophoblast p57kip2 -ve in complete mole villous cytotrophoblast p57kip2 +ve in partial mole syncytiotrophoblast always p57kip2 –ve An interesting finding is that the non-villous (extravillous or intermediate) trophoblast is p57kip2 positive even in complete mole [10]. As yet, there is no satisfactory biological explanation for this interesting phenomenon. Combined digital image ploidy analysis and p57kip2 can now be used in a complementary way to facilitate the diagnosis of complete and partial mole [8]. Suspected diagnosis Flow cytometry Image cytometry p57kip2 status Revised diagnosis Partial mole Diploid* Triploid* +ve Partial mole Complete mole Triploid Triploid +ve Partial mole Partial mole Diploid Diploid -ve Complete mole Partial mole Diploid Diploid +ve Hydropic miscarriage * Note greater reliability of digital image analysis compared with flow cytometry Twin molar pregnancy twin molar pregnancies are dizygotic gestations Normal fetus and mole or two moles together One case report published as "twin molar gestation" actually comprised 2 x normal fetuses and 2 x complete moles i.e. quads Incidence of 1:22 000 to 1:100 000 pregnancies Association with infertility treatments and IVF Increased risks of obstetric complications in twin molar pregnancies Persistent gestational trophoblastic disease in 20-55%(14 – 20% in non-twin mole) Metastatic disease (27.7%) (16% in non-twin mole) Poor survival rate of the normal twin (24 - 38%) Spontaneous abortion (43%) Severe pre-eclampsia (6%) Others (antepartum haemorrhage, thyrotoxicosis) Cases of twin molar gestations comprising a complete mole with coexisting fetus are often misinterpreted as partial molar singleton pregnancies [11]. Ectopic molar pregnancy Rare, mostly tubal 40 cases of tubal mole in world literature Over diagnosed because histopathologists do not appreciate the exuberance of normal trophoblast in the early first trimester [12, 13] Tertiary histopathological review is essential Normal early placentation shows: Absent/mild circumferential trophoblast excess Absent/mild hydrops Inconspicuous stromal apoptosis Mild/moderate scalloping of villi Persistent trophoblastic disease (PTD) PTD is not a histopathological diagnosis. It includes: invasive mole choriocarcinoma PTD occurs in 15-20% of patients with complete mole rare following partial mole – many early complete moles are misdiagnosed as partial moles the majority are invasive moles References Paradinas FJ, Elston CW. Gestational Trophoblastic Diseases In: Haines & Taylor Obstetrical and Gynaecological Pathology, Fifth edition Editors H Fox, M Wells, Churchill Livingstone 2003: 1359-1430. Genest DR. Partial hydatidiform mole; clinicopathological features, differential diagnosis, ploidy and molecular studies, and gold standards for diagnosis. Int J Gynecol Pathol 2001; 20: 315-322. Fukunaga M, Katabuchi H, Nagasaka T, Mikami Y, Minamiguchi S, Lage JM. Interobserver and intraobserver variability in the diagnosis of hydatidiform mole. Am J Surg Pathol 2005; 29: 942-947. Sebire NJ, Makrydimas G, Agnantis NJ, Zagorianakou N, Rees H, Fisher RA. Updated diagnostic criteria for partial and complete hydatidiform moles in early pregnancy. Anticancer Res 2003; 23: 1723-1728. Genest Dr, Ruiz RE, Weremowicz S, Berkowitz RS, Goldstein DP, Dorfman DM. Do nontriploid partial hydatidiform moles exist? A histologic and flow cytometric reevaluation of nontriploid specimens. J Reprod Med 2002; 47; 363-368. Kim MJ, Kim KR, Ro JY, Lage JM, Lee HI. Diagnostic and pathogenetic significance of increased stromal apoptosis and incomplete vasculogenesis in complete hydatidiform moles in very early pregnancy periods. Am J Surg Pathol 2006; 30: 362-369. Jun SY, Ro JY, Kim KR. p57kip2 is useful in the classification and differential diagnosis of complete and partial hydatidiform moles. Histopathology 2003; 43; 17-25. Crisp H, Burton JL, Stewart R, Wells M. Refining the diagnosis of hydatidiform mole: image ploidy analysis and p57KIP2 immunohistochemistry. Histopathology 2003; 43: 363-373. Merchant SH, Amin MB, Viswanatha DS, Malhotra RK, Moehlenkamp C, Joste NE. p57KIP2 immunohistochemistry in early molar pregnancies: emphasis on its complementary role in the differential diagnosis of hydropic abortuses. Hum Pathol 2005; 36; 180-186. Sebire NJ, Lindsay I. p57KIP2immunostaining in the diagnosis of complete versus partial hydatidiform moles. Histopathology 2006; 48: 873-874. Hancock BW, Martin K, Evans C, Everard JE, Wells M. Twin mole and viable fetus: the case for misdiagnosis. J Reprod Med (in press). Burton JL, Lidbury EA Gillespie AM, Tidy JA, Smoth O, Lawry J, Hancock BW, Wells M. Over-diagnosis of hydatidiform mole in early tubal ectopic pregnancy. Histopathology 2001; 38: 409-417. Sebire NJ, Lindsay I, Fisher RA, Savage P, Seckl MJ. Overdiagnosis of complete and partial hydatidiform mole in tubal ectopic pregnancies. Int J Gynecol Pathol 2005; 24; 260-264.