**1. Introduction**

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26 Skin Biopsy - Diagnosis and Treatment

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This chapter reviews the clinical presentation, histopathology, immunoprofile and molecular features of Langerhans cell neoplasms of the skin including Langerhans cell histiocytosis (LCH) and its malignant counterpart, Langerhans cell sarcoma (LCS). Biopsy of the skin is a useful method to confirm LCH/LCS diagnosis, as cutaneous involvement is seen in more than 50% cases. Skin can be the only presenting site of LCH, but it is usually seen as an integral part of multisystemic disease involvement.

Langerhans cells (LC) are bone marrow-derived antigen presenting cells [1]. Although LC, dendritic cells and monocytic/histiocytic cells share a common multipotential progenitor cells that reside in the bone marrow, to the date, myeloid derived macrophages and dendritic cells constitute divergent lines of differentiation from bone marrow precursors [2]. However, recent evidence demonstrates that LC can be generated from lymphoid-committed CD4low precur‐ sors, suggesting the role of lineage plasticity/ trans-differentiation and clonal infidelity [3-4].

LC can be found in the epidermis and mucosal lining of multiple organs including cervix, vagina, stomach and esophagus. The specific immunophenotypic profile is helpful distin‐ guishing LCs, as they can express CD1a and langerin (CD207); in addition the detection of Birbeck granules, seen in both pathological and resting LC is a prominent feature [5].

LCH encompasses a spectrum of disease characterized by an uncontrolled proliferation of LC [5]. The etiology of LCH/LCS is unknown in most cases, and there is not clear understanding of the pathogenesis. Although LCH is believed to be a clonal proliferation of LC [2, 6], the exact nature is controversial, as pulmonary LCH is thought to be a reactive/inflammatory disorder rather than a neoplastic process, and spontaneous remissions have been documented [7-8]. In a recent study of well characterized LCH cases, 30% had clonal immunoglobulin heavy chain (IGH@), immunoglobulin kappa light chain (IGK@) or T-cell receptor gamma (TCRG@) gene

© 2013 Bohn et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

rearrangements, suggesting a close relationship between LCH and lymphoid lineage [3]. Additional data that suggests LCH is in fact a clonal disease is the presence of specific mutations such as BRAF V600E, which have been found in up to 76% of tumors in children <10 years of age [7, 9].
