ALK-Negative Systemic Anaplastic Large Cell Lymphoma with Cutaneous Involvement Initially Mimicking Primary Cutaneous Disease: A Case Report.

Anaplastic large cell lymphoma (ALCL), a subgroup of T-cell non-Hodgkin's lymphoma, is a relatively uncommon malignancy with a highly variable prognosis. Systemic ALK-negative status and high Ki-67 expression are generally associated with poor outcomes in ALCL patients. Systemic ALK-negative ALCL presenting initially with cutaneous involvement is rare, with only a few cases reported in the literature. The aggressive clinical course of systemic ALK-negative ALCL with cutaneous lesions contrasts sharply with the indolent behavior of primary cutaneous ALCL (C-ALCL). Accurate distinction requires integration of histopathological and immunophenotypic findings. In particular, negativity for cutaneous lymphocyte antigen (CLA) is a useful discriminator, as primary C-ALCL typically expresses CLA while systemic cases often do not. Accumulating more clinical data is essential to better characterize this entity and guide therapeutic decisions. Here, we report a case of aggressive ALK-negative systemic ALCL that presented with cutaneous nodules as the initial manifestation, clinically mimicking primary C-ALCL.