Teaching Case 12

Clinical Summary

32-year-old female who presented with late first trimester spontaneous abortion.

Summary of Histologic, Immunophenotypic, and In Situ Hybridization Findings

The placenta is remarkable for enlarged placental villi often showing hydropic changes, mild trophoblastic hyperplasia, occasional scalloping and rare trophoblastic inclusions (see Figure 1). By immunohistochemistry, the placental villi show uniform expression of p57(kip2) in cytotrophoblasts and villous stromal cells (see Figures 2 and 3), arguing strongly against a complete hydatidiform mole. Fluorescence in situ hybridization studies show an increased number of nuclei containing three signals, consistent with triploidy (see Figure 4), confirming the histologic impression of partial hydatidiform mole.

Figure 1. H&E-stained slide of enlarged placental villi showing mild trophoblastic hyperplasia, hydropic changes, scalloping, and rare trophoblastic inclusions.	Figure 2. p57(kip2) expression is noted in cytotrophoblasts and villous stromal cells of placental villi. Intervillous trophoblastic islands show strong p57(kip2) positivity and serve as internal controls.
Figure 3. p57(kip2) expression is noted in cytotrophoblasts and villous stromal cells of placental villi.	Figure 4. Fluorescence in situ hybridization studies using a chromosome 17 centromeric probe (green) show an increased number of nuclei containing three signals, consistent with triploidy.

Final Diagnosis

Partial hydatidiform mole, confirmed by immunohistochemistry and in situ hybridization studies.

Discussion

There is significant interobserver and intraobserver variability in the diagnosis of hydatidiform mole. This variability is often exacerbated by the early detection of moles in the first trimester^(1,2). Moreover, distinguishing partial hydatidiform moles from spontaneous hydropic abortions remains a diagnostic challenge. Since distinguishing between partial/complete hydatidiform mole (PHM/CHM) and hydropic spontaneous abortions (SA) can impact patient treatment, the use of ancillary studies including p57(kip2) and Ki-67 immunohistochemistry and interphase FISH may be helpful in supplementing morphology in the diagnosis of hydatidiform moles.

p57(kip2) is a cell cycle inhibitor (i.e., cyclin-dependent kinase inhibitor) and tumor suppressor that has the unique property of being encoded by a paternally imprinted, maternally expressed gene and can serve as an excellent marker to discriminate between complete hydatidiform moles and partial hydatidiform moles/spontaneous products of conception.

Figure 5. Determination of triploidy by fluoresence in situ hybridization studies using a centromeric chromosome 17 probe. Cases with greater than 5.4% of cells with three CEP-17 hybridization signals are considered triploid.

Because complete hydatidiform moles contain only paternal DNA, p57(kip2) expression is absent in cytotrophoblasts and intervillous stromal cells, but present in partial hydatidiform moles and spontaneous abortions which contain maternal DNA. As determined by Castrillon et al., loss of p57(kip2) expression in the setting of molar pregnancy is diagnostic of complete hydatidiform mole⁽⁴⁾. In their series, all partial hydatidiform moles and spontaneous losses with hydropic changes retain strong p57(kip2) expression. Fukunaga and others extended the findings of Castrillon et al. in a similar set of early products of conception^(5,6).

We retrospectively examined 111 cases (including 29 PHMs, 30 CHMs, and 52 SAs) that were submitted for routine evaluation to exclude hydatidiform mole. Histologic evaluation was performed using criteria established by Szulman and Surti⁽³⁾. p57(kip2) and Ki-67 immunohistochemistry interphase FISH using a centromeric chromosome 17 probe (Vysis, Downer's Grove, IL) were performed. Expression of p57(kip2) and Ki-67 was scored based on the percentage of cytotrophoblasts positive as follows: 1 (0-25%), 2 (26-50%), 3 (51-75%), 4 (76-100%) with loss of p57(kip2) defined as <25% of cytotrophoblasts positive. Non-overlapping villous stromal cells and cytotrophoblasts containing three hybridization signals were counted (average of over 400 cells per nuclei per case). Cases displaying >5.4% of cells with three CEP-17 hybridization signals (represents three standard deviations above the mean of a negative control group of SA cases) were considered positive. Loss of p57(kip2) and high Ki-67-defined proliferative rate (3.97+/- 0.2) were noted in 30 of 30 CHMs, whereas PHMs and SAs displayed no loss of p57(kip2) and had a significantly lower Ki-67 proliferative rate (2.37+/-1.25; p<0.05). An increased percentage of cells containing three chromosome 17 signals indicative of triploidy was noted in 29 of 29 PHMs (mean of 22.7%+/- 6.2%; n=29), compared to CHMs (1.3+/-0.9%; n=26) and SAs (2.1+/- 1.1%; n=52).

	Partial hydatidiform mole	Complete hydatidiform mole	Spontaneous hydropic products of conception
p57(kip2) expression	No loss of p57(kip2)	Loss of p57(kip2)	No loss of p57(kip2)
Proliferative index as  measured by MIB-1	Intermediate	High	Low to intermediate
Triploid/Diploid	Triploid	Diploid	Diploid

In summary, p57(kip2) and MIB-1 immunohistochemistry and interphase FISH are useful in the diagnosis of hydatidiform mole and are particularly helpful in cases in which morphology alone may not be definitive.

Morphological and immunohistochemical findings in a complete hydatidiform mole

Complete hydatidiform moles typically show more prominent trophoblastic hyperplasia (see Figures 6 & 7) and by immunohistochemistry show loss of p57(kip2) in cytotrophoblasts and villous stromal cells (see Figures 8 and 9) and a high Ki-67 defined proliferative index (see Figure 10).

Figure 6. H&E-stained sections of abnormal, hydropic villi showing prominent trophoblastic hyperplasia.	Figure 7. Higher power view shows the marked trophoblastic hyperplasia within placental villi.	Figure 8. Loss of p57(kip2) expression within placental cytotrophoblasts and villous stromal cells.
Figure 9. High power view showing loss of p57(kip2) expression within cytotrophoblasts and villous stromal cells. Note that intervillous trophoblastic islands serve as internal controls.	Figure 10. High proliferative index as measured by MIB-1 staining noted within cytotrophoblasts in a complete hydatidiform mole.

References

1. Fukunaga M et al. Interobserver and intraobserver variability in the diagnosis of hydatidiform mole. Am J Surg Pathol. 29(7):942. 2005.
2. Hui P et al. Gestational Trophoblastic Diseases: Recent Advances in Histopathologic Diagnosis and Related Genetic Aspects. Adv Anat Pathol. 12(3):116. 2005.
3. Szulman AE and Surti U. The syndromes of hydatidiform mole. II. Morphologic evolution of the complete and partial mole. Am J Obstet Gynecol. 132(1):20. 1978.
4. Castrillon DH et al. Discrimination of complete hydatidiform mole from its mimics by immunohistochemistry of the paternally imprinted gene product p57KIP2. Am J Surg Pathol. 25(10):1225. 2001.
5. Fukunaga M. Immunohistochemical characterization of p57KIP2 expression in early hydatidiform moles. Hum Pathol. 33(12):1188. 2002.
6. Crisp H et al. Refining the diagnosis of hydatidiform mole: image ploidy analysis and p57KIP2 immunohistochemistry. Histopathology. 43:363. 2003.