Background: Transformation into a high-grade lymphoma in cutaneous T-cell lymphoma (CTCL) occurs in approximately 25% of cases and is associated with an aggressive clinical course.

Methods: We identified four cases of transformation of Sézary syndrome (SS) into pleomorphic T-cell lymphoma.

Results: In all patients, transformation occurred first in the lymph nodes, an average of 43 months after the diagnosis of SS. These high-grade lymphomas were composed of CD30-positive (two patients) and CD30-negative (two patients) pleomorphic large cells. All patients died of lymphoma an average of 29 months after nodal transformation.

Conclusions: Because of an apparently poorer prognosis, the early recognition of transformation, especially by lymph node biopsy, is important for adequate therapy.