Clinicopathologic Characteristics, Treatment Outcomes of Pediatric Mycosis Fungoides in Turkey: A National Multicenter Retrospective Cohort.

BACKGROUND AND OBJECTIVES: This study aimed to characterize the clinical spectrum, diagnostic delay, treatment patterns, and outcomes of pediatric mycosis fungoides (MF) and to identify predictors of early response. METHODS: This national multicenter retrospective study included patients diagnosed with histopathologically confirmed MF before 18 years of age. Demographic, clinical, histopathologic, immunophenotypic, staging, treatment, and follow-up data were collected. Early response at 3-6 months (partial/complete response) was analyzed using logistic regression. RESULTS: A total of 133 patients were included; 60.9% (81/133) were male. Median age at diagnosis was 13 years (IQR, 9-15) and median diagnostic delay was 18 months (IQR, 8-48). Classic morphology was recorded in 78.2% (104/133), and hypopigmented MF in 36.1% (48/133); overlapping morphologies were documented in 42.1% (56/133). Stage IA disease was present in 59.4% (79/133). Phototherapy was used in 60.9% (81/133). Early response occurred in 91.0% (121/133). BSA < 10% was independently associated with higher odds of early response (aOR 8.42, 95% CI 1.71-41.54; p = 0.009), whereas older age at diagnosis predicted lower odds (aOR 0.81 per year, 95% CI 0.67-0.98; p = 0.029). Relapse occurred in 28.5% (37/130) within median follow-up of 22 months (median time to relapse of 8 months); 67.6% (25/37) relapsed within 12 months. CONCLUSION: In this cohort, pediatric MF presented at an early stage. Despite favorable early responses, relapse occurred in nearly one third, often within the first year, supporting long-term surveillance. Higher BSA involvement and older age at diagnosis were associated with reduced early response.