Introduction

Classification of cutaneous lymphomas

The skin is the second most common site of extranodal lymphoma after the gastrointestinal tract [1]. The term primary cutaneous lymphoma refers to cutaneous lymphomas that present in the skin with no evidence of extracutaneous disease at the time of diagnosis [2].

This chapter adopts the 2005 WHO/EORTC classification (Table 26.1) for cutaneous lymphomas [2, 3]. Prior to its publication, the two classification schemes most widely used were the 2001 World Health Organization (WHO) classification [4] and the 1997 European Organization for the Research and Treatment of Cancer (EORTC) classification [5].

The 2005 WHO/EORTC classification is a consensus system based on the premise that primary cutaneous lymphomas often have a completely different clinical behavior and prognosis from histologically similar nodal lymphomas: therefore, they require different management strategies and treatment. This new classification is validated by clinical follow-up data on 1905 patients from the Dutch and Austrian registries for primary cutaneous lymphomas [6].

Epidemiology in the pediatric age group

Primary cutaneous lymphomas are extremely rare, with an incidence of approximately 0.36 per 100 000 [7] persons per year. Cutaneous T-cell lymphomas (CTCLs) account for approximately 75% of all cutaneous lymphomas in Europe [5] and >90% in North America. Although typically considered a disease of adulthood (approximately 75% of patients are diagnosed after 50 years of age [8]), pediatric cases make up from 4 to 11% of CTCL cases, and many adult patients report initial onset in childhood [8–10].