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DEVELOPMENT OF A SILVER IN-SITU HYBRIDISATION-BASED ASSAY FOR THE DETERMINATION OF PLOIDY STATUS IN MOLAR PREGNANCY DIAGNOSIS

Aim: To establish a scoring method for ploidy analysis by a silver in-situ hybridisation-based assay (SISH) using the chromosome 17 probe. Methods: SISH using the chromosome 17 probe was performed on formalin fixed paraffin sections of archival cases of complete hydatidiform moles, partial hydatidiform moles and hydropic products of conception at Austin Pathology with previously confirmed ploidy status (determined by either flow cytometry or karyotyping at the Royal Women's Hospital, Parkville, Victoria). In order to determine the ploidy status a scoring method was developed based on the average number of signals per nucleus (ASN) and the percentage of nuclei with three signals (NS) in 50 villous cytotrophoblasts and/or stromal cells. The results of four independent observers were compared individually and collectively with ploidy status assessed by flow cytometry or karyotyping. Results: There was a highly significant difference between diploid and triploid gestations 1.86 ± 0.13 and 2.70 ± 0.16 respectively (Student t-test, p < 0.0001) for ASN and 1.14 ± 1.65 and 71.59 ± 14.25 respectively (Student t-test, p < 0.0001) for NS. The sensitivity and specificity of the SISH-based assay was 99.1% and 100% respectively for ASN and 100% and 100% respectively for NS. Conclusions: This single probe SISH-based assay can reliably distinguish between diploid and triploid gestations.