Aim: To determine whether immunohistochemical staining for p57(KIP2), the product of the maternally expressed gene CDKN1C, can be used to differentiate between gestational trophoblastic tumours arising from a complete hydatidiform mole and those originating from non-molar pregnancies.
Methods: The immunohistochemical expression of p57(KIP2) was investigated in 23 cases of choriocarcinoma and 17 placental site trophoblastic tumours. Fourteen of the tumours examined were shown by DNA analysis to have arisen from complete hydatidiform moles and 26 from non-molar pregnancies.
Results: Five of 11 (45%) post-complete hydatidiform mole choriocarcinomas and two of three (67%) post-complete hydatidiform mole placental site trophoblastic tumours were found to be p57(KIP2)+ and showed similar immunostaining characteristics to tumours that developed from non-molar pregnancies. Although there was a statistically significant reduction in the proportion of cases showing positive p57(KIP2) staining in post-complete hydatidiform mole tumours compared with those originating in non-molar pregnancies [proportion difference 0.35 [95% confidence interval (CI) 0.05, 0.61], P = 0.02], immunostaining did not provide diagnostically useful information to differentiate between these tumours in clinical practice. There was no significant difference between the extent of staining in choriocarcinoma versus placental site trophoblastic tumours [proportion difference 0.17 (95% CI - 12, 42), P = 0.19]. The majority of both types of gestational trophoblastic tumour were positive for the presence of the p57(KIP2) protein irrespective of their genetic origin.
Conclusion: Immunostaining for p57(KIP2) fails to discriminate between gestational trophoblastic tumours that have arisen from complete hydatidiform moles and those that have originated from other types of pregnancy.