Diagnostic utility of p57 immunohistochemistry and DNA ploidy analysis by fluorescence in situ hybridisation in hydatidiform moles

Hydatidiform moles (HMs) include complete and partial moles, are the result of abnormal fertilisation. The accurate classification of HMs and its distinction from non-molar specimens is utmost important for clinical management and risk assessment. It is diagnostically challenging if the distinction is based solely on histomorphology with poor interobserver reproducibility, especially in early gestations. This study aimed to investigate the diagnostic ability of combined p57 immunohistochemistry and DNA ploidy analysis to distinguish between complete moles, partial moles and non-molar abortus. We included all HMs cases diagnosed in our centre over a six-year period. p57 immunohistochemistry stain was performed. Only nuclear immunoreactivity in >50% of cytotrophoblasts and villous stromal cells was regarded as positive for p57. DNA ploidy status was determined by fluorescence in situ hybridisation. A total of 250 cells from five chorionic villi were counted and were scored as diploid or triploid if more than 10% of nuclei demonstrated two or three signals, respectively. A total of 51 cases originally diagnosed by histomorphology as complete mole (n = 18), partial mole (n = 24) and non-molar abortus (n = 9) were recruited. The cases were reclassified based on the p57 immunostaining pattern and DNA ploidy status, into 27 complete moles (p57-/diploid), 9 partial moles (p57+/triploid) and 15 non-molar abortus (p57+/diploid). The diagnostic accuracy by histomorphological features alone in each category: complete moles, partial moles and non-molar abortus was 78.4%, 70.6% and 88.2% respectively. This study highlighted the importance of the utility of combined p57 immunostain and DNA ploidy analysis in arriving at an accurate diagnosis in HMs. An algorithmic approach utilising these ancillary techniques is advocated in routine diagnostic workup for a more refined diagnostic approach to HMs.