Development of a Chromosomal Microarray Test for the Detection of Abnormalities in Formalin-Fixed, Paraffin-Embedded Products of Conception Specimens

Testing the products of conception (POCs) provides information about the cause of fetal loss and helps determine the recurrence risk of future losses and chromosome abnormalities in subsequent pregnancies. Historically, the Mayo Clinic Cytogenetics Laboratory performed targeted fluorescent in situ hybridization (FISH) testing to identify aneuploidy of only certain chromosomes in formalin-fixed, paraffin-embedded (FFPE) POC samples. Chromosomal microarray studies using the Affymetrix OncoScan FFPE Assay can detect copy number changes across the genome. We validated the utility of the OncoScan assay using 25 archival FFPE POC specimens with previous FISH results (five normal, 12 trisomy, six triploidy, two monosomy). Of the five normal samples, four had no clinically relevant findings, and one sample was found to have trisomy 9, which is not detectable by the FISH test. For the 20 samples with abnormal FISH results, the OncoScan assay identified all reported abnormalities along with additional findings. A sample with trisomy 22 was also found to have trisomy 7. Another sample reported as triploidy was found to have four copies of chromosome 16. In conclusion, we verified the performance characteristics of OncoScan on FFPE POC specimens and found it acceptable for clinical use. Additional information was identified in 3 of 25 cases (12%) that would explain the pregnancy loss or provide recurrence risk for the family.