In respect to the concept of nosologic entities as defined by recent lymphoma classifications the diagnostic evaluation of primary cutaneous lymphomas includes the integration of clinical, morphological, phenotypic, and molecular characteristics. Several studies have demonstrated that the diagnostic accuracy employing clinical and histo-logical features alone ranges from 50% to 75%, but reaches 80% when morphologic features are combined with the immunophenotypic or genotypic characterization of tumor cells (1). Immunohistochemical (IHC) identification of the tumor cell pheno-type plays such a crucial and invaluable role in the diagnostic work-up of cutaneous lymphoma (CL) that it can be regarded as a mandatory step in establishing the correct diagnosis (2). Moreover, several forms of CL such as cytotoxic lymphomas can only be correctly identified by phenotyping. On the other hand, identical phenotypes and cyto-morphologic changes can be seen in clinically and prognostically different CL. Thus, the final diagnosis has always to be based on integrative synopsis of all clinical, histo-pathological, IHC, and molecular biological findings.
During the last decade, almost all antibodies necessary for adequate classification of CL became commercially available and applicable for archival, i.e., formalin-fixed and paraffin-embedded tissue (3,4). Performing IHC in CL, one has to be aware of various pitfalls and practical aspects (5). There is a need for standardization of IHC to facilitate comparison between different laboratories and antibodies.
Table 1 lists a set of the antibodies, which are useful for the diagnosis of the vast majority of CL. The diagnostic value of these antibodies and some of the pitfalls of IHC will be discussed in the balance of this section.
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