Is it reliable to use paraffin embedded tumor tissues as biological evidence in parentage cases?

Abstract

Short tandem repeats (STR) are reliable markers used for forensic identification and paternity testing. In some cases, histological paraffin blocks containing malignant cells can be used for STR typing in identification and paternity. DNA profiling and result interpretation with these samples often becomes a challenging job. The malignant tissues may show preferential amplification, loss of heterozygosity, and microsatellite instability.Due to the suspected paternity case, two paraffin blocks were sent for DNA analysis by Court of Justice. Pathology report of the paraffin blocks have shown that they contain lung cancer tissues taken with bronchoscopy. After extracting DNA with silica based method from the samples taken from different parts of these two blocks, 21 autosomal STR loci and 17 gonosomal STR loci were studied.When we have compared the STR profiles of son and his alleged father, Y-chromosomal STR loci matched fully. But for 2 of the 21 autosomal STR loci were found mismatches in father-son comparing. These two mismatched loci have been homozygous in alleged father. Moreover, 10 of 21 autosomal loci have shown homozygosity, and at one locus D16S539 has three alleles. While increased homozygosity in FFPE sample of alleged father has increased the paternity index, mismatched loci have lessened it in our model with mutations but without dropout.These results suggest that great care and proper statistical model should be taken in the evaluation of the DNA typing results obtained from clinical cancerous specimens, in particular when no other reference samples containing normal tissue are available.