Best practices in diagnostic immunohistochemistry: Workup of cutaneous lymphoid lesions in the diagnosis of primary cutaneous lymphoma

Context. - Primary cutaneous lymphoma is a common extranodal non-Hodgkin lymphoma. These lesions share common features with their nodal counterparts, but also have differences in morphology, unique clinical presentations, and immunohistochemical features. Objective. - To review the 2008 World Health Organization (WHO) and 2005 consensus WHO-EORTC (European Organisation for Research and Treatment of Cancer) classifications, and address the immunohistochemical findings in the most common primary cutaneous T- and B-cell lymphomas. Since clonality testing is commonly used as an ancillary test in the evaluation of cutaneous lymphoma, a brief section in the use and pitfalls of clonality testing is included. Data Sources. - The WHO and EORTC classification publications and the relevant recent literature were used to compile appropriate and practical guidelines in this review. Conclusions. - The practice of dermatopathology and hematopathology varies widely. Thus, while this review provides an overview and guideline for the workup of lymphoid lesions of the skin, the practitioner should understand the importance of clinical correlation as well as appropriate utility of available resources (such as clonality testing) in arriving at a diagnosis in cutaneous lymphoid lesions.