In this first of 2 special issues of Advances in Anatomic Pathology, we present an update on the use of immunohistochemistry in surgical pathology within specific subspecialties. We begin with a series of review articles covering immunohistochemistry use in thoracic, genitourinary, soft tissue, and endocrine pathology, as well as a rare perspective on coding, billing, and compliance regulations relevant to immunohistochemistry utilization.
Initially used almost exclusively as a diagnostic adjunct for surgical pathologists, immunohistochemistry has increasingly assumed an expanded role in patient care. HER2 testing is a prime example of immunohistochemistry as a surrogate for underlying molecular alterations that are predictive of drug response. Another example is immunohistochemistry for ALK in lung adenocarcinomas. This use is rapidly expanding as more drugs are associated with companion immunohistochemical assays. A recent example is the emergence of PD-L1 and mismatch repair protein evaluation by immunohistochemistry across many tumor types for identification of appropriate patients for immune checkpoint inhibitor therapy. Immunohistochemistry use as a surrogate for germline alterations predisposing to cancer syndromes has also become a reality. For example, our knowledge of the spectrum of succinate dehydrogenase mutation-associated neoplasms has greatly expanded over the past decade, in part due to the availability of commercial SDHB antibodies. While these newer applications of immunohistochemistry are emphasized, we have not forgotten its standard use to “make a diagnosis.” Lineage-restricted immunohistochemical markers continue to play a central role in tumor diagnosis, supplemented by markers that serve as surrogates for molecular genetic alterations, in some cases obviating molecular testing. As the list of available antibodies continuously expands, the selection of diagnostic markers for routine daily practice can become overwhelming. It is our hope that these articles will also help distill some of this information and aid in menu selection for diagnostic laboratories.
We are confident these reviews will provide the reader with a thorough, yet concise, update on the ever expanding role of immunohistochemistry in diagnostic surgical pathology.