Identity determination in diagnostic surgical pathology.

From a technical perspective, specimen identity determination in surgical pathology over the last several decades has primarily focused on analysis of repetitive DNA sequences, specifically microsatellite repeats. However, a number of techniques have recently been developed that have similar, if not greater, utility in surgical pathology, most notably analysis of single nucleotide polymorphism (SNPs) and gene panels by next generation sequencing (NGS). For cases with an extremely limited sample or a degraded sample, sequence analysis of mitochondrial DNA continues to be the method of choice. From a diagnostic perspective, interest in identity determination in surgical pathology is usually centered on resolving issues of specimen provenance due to specimen labeling/accessioning deficiencies and possible contamination, but is also frequently performed in cases for which the patient's clinical course following definitive therapy is remarkably atypical, in cases of an unexpected diagnosis, and by patient request for "peace of mind". However, the methods used for identity determination have a much broader range of applications in surgical pathology beyond tissue provenance analysis. The methods can be used to provide ancillary information for cases in which the histomorphology is not definitively diagnostic, as for example for tumors that have a virtually identical microscopic appearance but for which the differential diagnosis includes synchronous/metachronous tumors versus a metastasis, and for the diagnosis of hydropic early gestations versus hydatidiform molar pregnancies. The methods also have utility in several other clinical settings, for example to rule out a donor-transmitted malignancy in a transplant recipient, to monitor bone marrow transplant engraftment, and to evaluate natural chimerism.