INTRODUCTION: Hydatidiform mole (HM) is an abnormal gestation characterized by significant hydropic enlargement, trophoblastic proliferation and atypia involving part or all of the chorionic villi. The diagnosis and classification of hydatidiform moles is subject to great inter-observer variability due to significant morphologic overlaps. This study aims to evaluate the utility of p57KIP2 immunohistochemistry and ploidy by Her-2 FISH in refining the diagnosis of molar tissues.

METHOD: 113 and 78 molar cases were retrieved from the archives of the Histopathology Section of the Philippine General Hospital and Pathology Department of Seoul National University Hospital, respectively. TMA sections were submitted for immunohistochemical analysis for p57KIP2. Ploidy was determined by fluorescence in situ hybridization using Her-2 probe. An interrater reliability analysis was done using the Kappa statistics with 95% confidence interval.

RESULTS: All 68 (100%) cases diagnosed as CH were negative for p57KIP2 staining and are diploid. Among the 54 cases of PH, only 1 (2%) is positive for p57KIP2 and is diploid. The interrater reliability between p57KIP2 and Her-2 FISH ploidy results is 0.66 (p <.0.001), 95% CI (0.02, 1.00) which is considered "fair to good." The kappa value between review diagnosis and p57KIP2 is 0.024 while the kappa between review diagnosis and Her-2 FISH ploidy is 0.050 both signifying poor agreement beyond chance.

CONCLUSION: Morphologic assessment alone may not be sufficient in problematic cases. p57KIP2 in conjunction with by Her-2 FISH are good adjuncts in the diagnosis and classification of hydatidiform mole.