ISCL/EORTC-CLTG/USCLC recommendations for the diagnosis, staging and treatment of early-stage paediatric mycosis fungoides: a modified Delphi consensus. Part one: diagnosis and staging.

Mycosis fungoides (MF) is considered rare in children and adolescents. Accumulating experience indicates that compared with adult patients, almost all paediatric patients with MF are diagnosed at an early stage of disease, exhibit higher rates of atypical presentations and follow a notably indolent course. Despite the need for special staging/investigations specific for children and adolescents, the staging of paediatric MF is currently based primarily on standard practice in adults. The aim of this work was to develop staging recommendations specifically designed for MF in children and adolescents, on behalf of the three largest societies for cutaneous lymphomas, the International Society for Cutaneous Lymphomas, the European Organisation for Research and Treatment of Cancer - Cutaneous Lymphoma Tumor Group, and the United States Cutaneous Lymphoma Consortium. We developed this guideline through an international expert consensus process and in accordance with the EQUATOR Network's recommendations for guideline development. A modified Delphi process was conducted, using questionnaires covering topics including the definition, characteristics and staging of paediatric MF. Two rounds of expert feedback were conducted, with an additional hybrid consensus meeting. We reached a consensus that the term 'paediatric MF' should be reserved for MF diagnosed at ≤ 18 years of age. Panellists specified the unique clinical characteristics of paediatric MF, including a high prevalence of hypopigmented and folliculotropic variants, and reached a consensus on the indolent nature of the disease during childhood and adolescence with rare progression to advanced stage. The consensus reached recommends that while the staging approach is largely similar to that in adults, imaging for early-stage paediatric MF should rely on ultrasound of the lymph nodes if indicated, rather than computed tomography with contrast or integrated with positron emission tomography. Along with this, clinicians should be aware that in children, palpable lymph nodes are common owing to the increased incidence of infectious diseases. In summary, this guideline addresses the major clinical characteristics of paediatric MF, which differ from those in adults, and provides practical staging recommendations considering the safety implications specific for this age group.