[Diagnostics of primary cutaneous lymphomas].

Primary cutaneous lymphomas can be diagnosed when the clinical symptoms, histology, immunohistology and molecular biological changes are characteristic of primary cutaneous T or B‑cell lymphomas; however, in many cases not all of the changes are typical of a primary cutaneous lymphoma especially in the early stages; therefore, the diagnosis of a primary cutaneous lymphoma can be a challenge. This is especially true for the Sézary syndrome, which can initially prove to be difficult to differentiate from reactive erythroderma; therefore, the main focus of this review is the diagnostics of Sézary syndrome. The review also summarizes the clinical heterogeneity and describes the classical histological and immunohistochemical changes for the diagnosis of Sézary syndrome. Recent data from different multicenter, international studies by the cutaneous lymphoma task force of the European Organisation for Research and Treatment of Cancer (EORTC) on dermatological alterations of the skin and the detection of Sézary cells in blood are addressed. The detection of Sézary cells in the blood still remains a challenge despite improved molecular boiological and cytogenetic characterization of tumor cells. The latest studies of the EORTC group particularly identified CD158k, MYC, MNT, DNM, TWIST1, EPHA4 and PLS3 as valuable markers for the differentiation of reactive erythroderma but which are not yet part of the standard diagnostics of Sézary syndrome. Further studies are required to see if these markers can be used in the routine clinical application.