Juvenile Mycosis Fungoides: A Multicenter Retrospective Italian Study

ABSTRACT Background Juvenile mycosis fungoides (JMF) is a rare cutaneous T‐cell lymphoma with onset in childhood or adolescence. Diagnosis is often delayed due to clinical resemblance to benign dermatoses. Compared to adult‐onset disease, JMF may exhibit distinct clinicopathological and immunophenotypic features. Management typically relies on skin‐directed therapies, though paediatric‐specific treatment guidelines are lacking. Objectives To characterise the clinical, histopathological, and immunophenotypic features of JMF, evaluate treatment responses, and assess long‐term outcomes in an Italian multicenter cohort. Methods We conducted a retrospective observational study involving five tertiary dermatology centres in Italy. Patients with biopsy‐confirmed MF and disease onset ≤ 20 years were included. Clinical, histological, immunophenotypic, treatment and follow‐up data were collected. Patients were stratified by age at onset (< 14 vs. ≥ 14 years) for subgroup analysis. Results Twenty‐nine patients were included (median age at onset: 12 years). The most common clinical variants were classic erythematous MF (41%) and hypopigmented MF (28%), the latter associated with longer diagnostic delay. A CD8⁺‐predominant phenotype was found in 52% of evaluable cases. A personal or familial atopic diathesis was reported in 44% of patients, including a personal history of atopic dermatitis in 31%, which was significantly more frequent in children under 14 years ( p = 0.027). Most patients presented with stage IA disease (79%) and received skin‐directed therapies. The overall response rate to first‐line treatment was 90% (59% complete remission, 31% partial remission), with no cases of progression. At final follow‐up (median 8.1 years), patients with disease onset before 14 years were more likely to be disease‐free (65% vs. 22%, p = 0.044). Conclusions JMF typically presents with early‐stage disease and responds well to skin‐directed therapy. Hypopigmented variants and CD8⁺ immunophenotype are frequent. A younger age at onset may predict better long‐term disease control.