p57KIP2 immunohistochemical expression: a useful diagnostic tool in discrimination between complete hydatidiform mole and its mimics.

PURPOSE: The purpose of this study was to evaluate the results of immunohistochemical expression of p57KIP2 in the complete hydatidiform mole (CHM) and other types of hydropic pregnancy.

BACKGROUND

Classification of molar pregnancies is typically defined by histologic and genetic criteria. The histologic criteria are subjective and demonstrate considerable interobserver variability. Several studies have recently shown that immunohistochemical detection of p57KIP2 expression in molar pregnancies is a useful ancillary diagnostic tool. The p57KIP2 gene is strongly paternally imprinted and maternally expressed. The villous cytotrophoblastic cells of complete hydatidiform mole (CHM) lack the maternal genome, that's why they reveal negative immunostaining for p57KIP2. On the contrary, in villous cytotrophoblastic cells of partial hydatidiform mole (PHM) and hydropic abortion, immunohistochemical staining for this marker is positive.

METHODS

We performed p57KIP2 immunohistochemical staining in 89 cases in four histological diagnostic categories as follows: "CHM" (n = 22), "PHM" (n = 32), "hydatidiform mole (HM)" (where the histological features were insufficient to differentiate between CHM and PHM) (n = 20), and "suggestive for PHM" (n = 15).

RESULTS

p57KIP2 expression in villous cytotrophoblasts and stromal cells was absent or markedly reduced in 22 of 22 "CHMs", 7 of 32 "PHMs", 15 of 20 "HMs", and 1 of 15 "suggestive for PHMs" (P < 0.001). In all cases, maternal decidua and syncytiotrophoblast, respectively, showed diffuse and strong p57KIP2 expression, and negative p57KIP2 expression.

CONCLUSIONS

This study confirms that negative p57KIP22 immunostaining may reliably identify CHM irrespective of gestational age and can be used in association with the histological findings to distinguish CHM from its mimics in challenging cases.