Cutaneous B cell lymphomas: standards in diagnostic and clinical work-up. Hints, pitfalls and recent advances.

This review focuses upon the pragmatic diagnostic approach of suspicious B cell infiltrations in the skin and lists the necessary histopathological and molecular tools for a thorough work-up. We start with the description of different histopathological patterns of cutaneous B cell infiltrations and recommend pattern-dependent immunohistochemical staining algorithms for further differential diagnosis. A summarised description of the current World Health Organisation (WHO) subtypes of primary cutaneous B cell lymphomas highlighting their most relevant clinical, histopathological and molecular features is included. Differential diagnostic clues towards secondary infiltrations by systemic B cell lymphomas, B cell-rich T cell lymphoproliferative disorders and pseudolymphomas are provided. Furthermore, the most important pitfalls also elaborating on rare differential diagnoses are highlighted with helpful hints to solve arising diagnostic difficulties. The clinical work-up and the staging examinations depending on the type of B cell infiltrate are relevant for patient care and a short overview of the main diagnostic standards is given.