Introduction
Normal T-lymphocytes express either αβ or γδ T-cell receptors, while γδ T-cells comprise 0.5%–10% of total T-cells with variable distribution in mucosa, spleen, lymph node and other sites, that play critical roles of innate and adaptive immunity.1 The physiological development and immunophenotype of γδ T-cells are different from αβ T-cells.2 For instance, subsets of γδ T-cells are less dependent on thymic microenvironment and may arise extrathymically.1-3 The γδ T-cells express CD3, variable CD5, variable CD56 and CD57, while they are often negative for CD4 and CD8.
T-cell lymphomas (TCLs) account for about 12% of the total lymphoid tumors, and comprise over 20 distinct entities in the World Health Organization (WHO) classifications.4 TCLs are extremely rare in children. Aside from T-lymphoblastic and anaplastic large cell lymphomas; the majority of TCLs originate from αβ T-cells and only few arise from γδ T cells, 4-6 including primary cutaneous γδ T-cell lymphoma (PCGDTCL), hepatosplenic T-cell lymphoma (HSTCL), and monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL).4 Patients with these types of γδ TCLs appear to have an aggressive clinical course and poor outcome despite aggressive chemotherapy and/or additional treatments.4Occasional γδ T-cell lymphoma cases are limited to the subcutis and show a less aggressive clinical course.3,7-10 Further, some cutaneous and subcutaneous TCLs and non-malignant skin conditions may demonstrate an increase in γδ T-cells, with uncertain significance.2-4,11,12
Hence, our current knowledge of γδ TCLs is mostly based on adult patients; and the pathological and clinical studies of pediatric γδ TCLs are scarce.13 Moreover, the spontaneous regression of cutaneous γδ T-cell clonal proliferation has been reported in inflammatory and in non-neoplastic disorders.14 In this study, we report the pathological and clinical features of three unusual patients from this unique pediatric multi-disciplinary cutaneous lymphoma clinic.