Basic immunohistochemistry for lymphoma diagnosis.

Immunohistochemistry is a technique that uses antigen-antibody interactions to detect specific proteins in cells. This technique has several essential applications in lymphoma diagnosis, including identifying the cell lineage and phase of maturation, detecting specific genetic alterations, visualizing the degree of cell proliferation, and identifying therapeutic targets. CD3 is a pan T-cell marker expressed on most of the mature T/NK-cell lymphomas, except for anaplastic large cell lymphoma, whereas CD20 is a pan B-cell marker that is expressed on most of the mature B-cell lymphomas. CD79a may be a good alternative to CD20, compensating for its loss owing to the plasmocytic differentiation of tumor cells or history of rituximab administration. CD56, a neuroendocrine marker, is used as an NK cell marker in lymphoma diagnosis. Characteristic translocations occurring in follicular lymphoma () and mantle cell lymphoma () can be detected by the overexpression of Bcl-2 and cyclin D-1 in immunohistochemistry, respectively. Ki-67 reflects the degree of tumor cell proliferation by indicating cells in cell cycle phases other than G0. With the development of immunotherapy, several antibodies against markers such as programmed death-ligand 1 (PD-L1), CD19, and CD30 have been used as biomarkers to identify therapeutic targets. It is critical to properly fix the specimens to obtain accurate immunohistochemical results. Therefore, all processes, from tissue collection to the final pathological diagnosis, must be performed appropriately for accurate lymphoma diagnosis.