Pediatric Primary Cutaneous CD8+ Aggressive Epidermotropic Cytotoxic T-Cell Lymphoma With Unusually Long Clinical Course.

Primary cutaneous aggressive epidermotropic CD8+ cytotoxic T-cell lymphoma (PCAECTCL) is a rare and aggressive malignancy, with limited documented cases in pediatric patients. This report presents a unique case of a 9-year-old female with PCAECTCL, characterized by widespread erythematous annular lesions that exhibited an indolent clinical course that lasted four years after the development of the initial lesion, contrasting with the typically rapid progression seen in adults. Histopathological and immunohistochemical analyses revealed an atypical CD8+ T-cell infiltrate with marked epidermotropism, loss of CD2 and CD5 expression, and positivity for cytotoxic markers TIA-1 and granzyme B. Molecular studies identified a PCM1::JAK2 gene fusion, linking the disease to JAK/STAT pathway dysregulation, which is a finding previously unreported in pediatric PCAECTCL. Despite partial responses to topical therapies, oral prednisone, and methotrexate, the disease persisted, highlighting therapeutic challenges. This case underscores the importance of molecular profiling in PCAECTCL and suggests potential utility for JAK inhibitors like ruxolitinib.