Clinical presentation, immunopathology, and treatment of juvenile-onset mycosis fungoides: A case series of 34 patients

Background Mycosis fungoides (MF), the most common form of cutaneous T-cell lymphoma, typically presents in middle-aged to elderly individuals. Objective We sought to study the demographics, clinicopathologic features, treatment response, and prognosis of patients with biopsy-proven MF diagnosed before 20 years of age. Methods Patients were identified from a prospectively collected database for retrospective analysis. Results Of 1902 patients with MF, 34 had juvenile-onset MF: 41% were stage IA, 56% were stage IB, and 3% were stage IIB at diagnosis. The male to female ratio was 1.1:1. The median age of symptom onset was 9 years (range 3-19 years), with a delay in diagnosis between 1 month and 14 years. Patients primarily presented with hypopigmented (53%), hyperpigmented (29%), and pink-violaceous (41%) patches/plaques. Immunohistochemistry revealed 39% with CD8⁺ immunophenotype, 67% of which had hypopigmented lesions. The phototherapy response rate in 21 patients was 81%. All patients who completely responded to narrowband ultraviolet B phototherapy had hypopigmented MF. Limitations This is a single cancer center study. Conclusion Juvenile-onset MF presents with early-stage disease with an overrepresentation of hypopigmented MF and CD8⁺ immunophenotype. Narrowband ultraviolet B is an effective treatment option for juveniles, especially for those with the hypopigmented variant.