Biomedical Research

Differential diagnosis between complete and partial hydatidiform mole is clinically important because of the difference in the risk of developing more malignant form of the molar diseases. In this report, the classical microscopic criteria were re-evaluated in the light of the immunohistochemistry of p57KIP2 in the attempt to establish robust morphological criteria for the differential diagnosis. Thirty-six consecutive cases clinically suspected to be hydatidiform mole were employed. The histological criteria were scored by three pathologists. The cases were categorized into three entities of the molar diseases in accordance with the immunohistochemistry of p57KIP2 and CD34. The diagnostic significance of the histological criteria was evaluated in a logistic regression model. Of 36 cases, the immunohistochemistry revealed that 28 were complete and 6 were partial hydatidiform mole, while 2 cases were hydropic abortion. A stepwise logistic regression analysis indicated that, among seven criteria studied, three of them (shape of villi, prevalence of villi with three types of trophoblasts, and predominance of villi with hydropic change) were useful to differentiate complete hydatidiform mole from partial one. This observation may be applicable in the pathological diagnosis of the molar diseases. Hydatidiform mole is a disease associated with missed abortion, which is pathologically characterized by enlarged chorionic villi. It has two major entities, complete and partial hydatidiform mole (CHM and PHM, respectively). Since CHM has a higher risk to be associated with invasive mole or choriocarcinoma both of which cause invasion into uterine myometrium and distant metastasis, the differential diagnosis between CHM and PHM is clinically important (5). Several histological criteria for the differential diagnosis were proposed. Such classical criteria include hydropic enlargement of villi, scalloping shape of villi, cistern formation, disappearance or collapse of the stromal vasculature, trophoblastic inclusion, and the proliferation of trophoblasts (5, 9). Even with such histological criteria, it is often difficult to distinguish CHM from PHM, and the cytogenetic examination has been a golden standard to diagnose the two entities; CHM has a karyotype of 46XX (sometimes 46XY or tetraploid) and all the chromosomes are paternal origin, while PHM has maternal and paternal chromosomes with a karyotype of 69XXY or 69XXX (1, 6, 8). Recently, the immunohistochemical method using anti-p57KIP2 antibody was introduced to the diagnosis of the molar diseases (2, 3). p57KIP2 is a product of a paternally imprinted gene, CDKN1C, which is an inhibitor of the cyclin-dependent kinases (2, 3, 10). Because CHM is androgenetic in origin, Address correspondence to: Riruke MARUYAMA, M.D. Surgical Pathology Branch, University Hospital, Shimane University, Izumo 693-8501, Japan Tel: +81-853-20-2426, Fax: +81-853-20-2425 E-mail: hm5995@med.shimane-u.ac. jp N. Ishikawa et al. 142 diaminobenzidine (Multimer and UltraView DAB respectively; Ventana, Tucson, AZ, USA) were employed to visualize the labeled antigens. Staining was done using an automated stainer (BenchMark LT; Ventana) according to the manufacturer’s direction. Heat-induced antigen retrieval was performed by pretreatment in the stainer (95°C, 8 min for p57KIP2 and 100°C, 4 min for CD34) of the sections incubated in 10 mM Tris/1 mM EDTA buffer (pH 8.5). Correlations between the histological scores were examined using Pearson’s ρ. Differences of the scores among the immunohistochemical diagnoses were tested by non-parametric Kruskal-Walis test. A logistic regression model for the differential diagnocytotrophoblasts are negatively stained with antip57KIP2, while they are positive in PHM and normal placental tissue (2, 3). This staining is therefore a reliable tool to differentiate CHM from other molar diseases. In the latter conditions, p57KIP2 protein is expressed also in intermediate trophoblasts and villous stromal cells. In contrast to it, syncytiotrophoblasts are consistently negative, which has been reported to indicate that p57KIP2 is not directly related to them and that they are terminally differentiated and nonproliferating cells (4). Based on these observations, we are interested in how appropriate the classical microscopic criteria are in the diagnosis of molar diseases. Although the concordance of the immunohistochemistry with the classical histological diagnosis was repeatedly examined (1–3, 8), there were few reports to reevaluate the usefulness of each histological criterion in the light of the immunohistochemistry. In this communication, we thus studied the classical microscopic criteria in the molar diseases diagnosed with the p57KIP2 and CD34 immunostaining. We found that a set of three microscopic criteria were still useful in the diagnosis of CHM. MATERIALS AND METHODS Thirty-six cases of missed abortion curetted either in Shimane University Hospital or in Shimane Prefectural Central Hospital between 1999 and 2007 were employed in the study. All the cases were clinically diagnosed as hydatidiform mole. Ages of the cases varied from 20 to 51 and the mean age was 33 ± 8 years old (mean ± SD). The study was approved by the local ethical committee of Shimane University School of Medicine and of Shimane Prefectural Central Hospital. Pathological samples were processed anonymously and stained with hematoxylin and eosin. Histological scoring of microscopic criteria was performed independently by 3 experienced pathologists who were blind of clinical diagnoses and of the immunohistochemical staining. Scores of each criterion used in the study are shown in Table 1. Averages of the scores evaluated by the three pathologists were used in the analysis. Immnunohistochemical staining was performed using a mouse anti-human p57KIP2 (× 50 dilution, clone 25B2; Novocastra, New Castle, UK) and a mouse anti-human CD34 monoclonal antibody (× 50 dilution, clone QBEnd 10; DAKO, Grostrup, Denmark). CD34 was used to label vascular endothelial cells. A peroxidase-labeled secondary antibody and Table 1 Microscopic criteria for molar diseases Hydropic change 3: Hydropic villi only 2: Some unclassified villi 1: Some normal villi 0: Normal villi only Vascular change 3: Collapsed vessels only or no vessels 2: Collapsed vessels dominant 1: Mixture of collapsed and open vessels 0: Open vessels dominant Cistern 3: No cistern formation with severe hydropic change 2: Probable cistern formation 1: Evident cistern formation 0: No cistern formation without hydropic change (i.e., normal villi) Shape of villi 3: Round and enlarged villi dominant 2: Mixture of round and irregular villi 1: Irregular villi dominant 0: Normal villi (round but without enlargement) Trophoblastic proliferation 3: Circumferential proliferation dominant 2: Mixture of circumferential and eccentric proliferation 1: Eccentric proliferation dominant 0: No abnormal trophoblastic proliferation Type of trophoblasts 3: Proliferation of the 3 types in > 90% of villi 2: Proliferation of the 3 types in > 50% of villi 1: Proliferation of the 3 types in < 50% of villi 0: Proliferation of the 3 types in < 10% of villi Trophoblastic inclusion 3: None with hydropic change 2: Partially observed 1: Diffusely observed 0: None with normal stroma Histology of hydatidiform mole 143 As we had only 2 cases of hydropic abortion, we performed a stepwise logistic analysis on the factors differentiating CHM from PHM. As shown in Table 5 A, the type of trophoblasts, the shape of villi, and the hydropic change remained as useful markers for the differential diagnosis. Table 5 B shows several examples of the diagnoses using the logistic model constructed based on the results shown in Table 5 A. Using this model, 26 of the 28 cases of CHM (sensitivity = 92.8%) and 4 of the 6 cases of PHM (specificity = 66.7%) were correctly diagnosed.