Highly sensitive DNA typing for detecting tumors transmitted by transplantation.

DNA typing of a variable number of tandem repeats (VNTRs) and of short tandem repeats (STRs) is a modern forensic method for the identification of biological material. In many cases, amplification by the polymerase chain reaction (PCR), especially of STRs, allows DNA typing of minute amounts of or degraded DNA. Here we describe the successful use of forensic DNA typing to clarify the origin of a malignant tumor. We report two cases of metastatic malignant melanoma of unknown origin that developed a few months after transplantation in two recipients of kidneys from the same donor. Fresh metastatic tissue and blood from the first recipient, reference DNA of the donor, and only paraffin-embedded tissue from the second recipient were available for analysis. To investigate whether the melanoma originated in the donor, DNA analysis of nine polymorphic loci was performed. The results of the analysis showed that, in both cases, the tumors were genetically different from the recipient DNA but matched the donor DNA. One incident of allele loss was attributed to a mutation event. We conclude that the metastatic melanoma in both recipients originated in the donor and was transmitted by renal transplantation.