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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., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Over the past decade, the many advances in immunohistochemical techniques have revolutionized the field of immunohistochemistry. Most notable is discovery of the use of heat for antigen retrieval, which permits consistent and reliable demonstration of antigens in routine surgical pathology specimens despite variations in the duration of fixation and tissue processing schedules. As a result, immunohistochemical studies play an increasingly important role in surgical pathology, such as help in rendering a diagnosis in a crushed specimen, classification of tumors, prediction of the likely origin of a carcinoma, demonstration of micrometastases, provision of prognostic information, and demonstration of microorganisms. To serve such purposes, immunohistochemical stains must be performed at a high standard with consistent and reproducible results. The stains must be interpreted cautiously in the appropriate context, and potential pitfalls such as endogenous biotin activity must be recognized. The increased demand for immunohistochemical tests raises the issue of cost containment, which can be achieved through a number of ways, such as deletion of nonvalue-added tests, deletion of antibodies that no longer serve a purpose, replacement of the conventional positive control with a multitissue control mounted on the same slides of the test cases, various means of savings on antibodies, and continuing to use "expired" antibodies. To keep abreast of modem developments in the field in this era of information explosion, the internet can play an important role by providing updated information or database and a platform for rapid exchange of knowledge.