2 - An overview of childhood lymphomas

Summary

INTRODUCTION

Lymphomas encompass a diverse group of neoplasms that arise from the clonal proliferation of lymphoid precursor cells. They are triggered by a series of genetic events that may be related to genetic predispositions, viral and other environmental factors, or may simply be accidental genetic rearrangements.

Lymphomas are the third most common cancer in children in the UK, behind acute leukaemias and brain tumours. They account for approximately 11–13% of all childhood malignancies with an annual incidence of 13.2 per million children [1]–[4]. The age-specific incidence rates and clinical features of paediatric lymphomas in white children in the USA correspond to those in Europe [5]. In equatorial Africa, 50% of all childhood cancers are due to lymphomas, because of the high incidence of Burkitt's lymphoma.

Paediatric lymphomas can be classified into Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL). The main subtypes are defined in the REAL classification [6], but the more recent WHO classification updates and expands this [7]. NHLs represent 60–70% of all childhood lymphomas in developed countries [2], [8], affecting children mainly between 7 and 10 years of age. The male-to-female ratio recorded in a Dutch study was 2.5 [5]. There is, however, an increased incidence in children with inherited or acquired immunodeficiencies [9], [10]. HL represents the remaining 30–40% of childhood lymphomas. Their incidence increases steadily throughout life and studies show a male-to-female ratio of 2.7 [5].

Unlike adult NHLs, which are often low-to-intermediate grade, the paediatric NHLs are frequently high-grade lymphomas and are clinically aggressive.