Diagnostic Pediatric Hematopathology

Mature T-cell lymphomas in children and adolescents comprise about 10–15% of the non-Hodgkin lymphomas (NHLs) observed. Unlike adults, where there is a broad spectrum of T-cell neoplasms, most mature T-cell disease in this age group is ALK (anaplastic lymphoma kinase)-positive anaplastic large cell lymphoma (ALCL, ALK positive), with other subtypes of T-cell lymphomas being much more rarely observed (Tables 22.1 and 22.2). Similarly, although NK-cell neoplasms are rare in adults, comprising approximately 1–2% of NHL (although with higher frequency in Asia and Latin America), these neoplasms are extremely rare in children and most appear in the literature as single case reports or small series. As in adults, mature T- and NK-cell lymphomas tend to present with a broad spectrum of clinical disease including nodal, extranodal, and leukemic diseases, and are frequently associated with paraneoplastic phenomena such as hemophagocytosis, fevers, rashes, and other manifestations that may be, in part, attributable to cytokines produced by the neoplastic cells [1, 2].

Epidemiology

Mature T- and NK-cell lymphomas are rarer than B-cell disease in North American and European populations. However, there are significant differences in geographic distribution, with higher incidences of T/NK-cell lymphoma in adults in Asia and Latin American populations than are seen in the United States and Europe. In Asia, T-cell lymphomas in adults make up 30–70% of all NHLs, whereas in the pediatric population they make up about 37% of cases [3, 4].