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Case Reports

Abstract

Mycosis fungoides (MF) is the most common variant of cutaneous T-cell lymphoma (CTCL), accounting for approximately 60% of cases. Although MF usually follows an indolent course, 20–55% of patients with advanced-stage disease may develop large cell transformation (LCT), often characterized by the emergence of CD30-positive large atypical lymphocytes. This transformation might signal a more aggressive clinical progression and can pose a diagnostic challenge.

We describe a 35-year-old woman with a five-year history of MF, previously treated with psoralen plus ultraviolet A (PUVA) therapy for hyperpigmented patches on her extremities. She later developed a rapidly enlarging, ulcerated lesion on her right leg. Histopathological examination showed a dense dermal infiltrate of large atypical lymphocytes with numerous mitotic figures. Immunohistochemistry demonstrated strong positivity for CD3, CD4, and CD30, consistent with MF with CD30-positive large cell transformation.

This case emphasizes the importance of considering LCT in MF patients who develop new or rapidly worsening lesions, particularly ulcerated nodules or tumors. Detecting CD30 expression in large atypical cells is crucial for confirming transformation and has treatment implications, as CD30-targeted therapies like brentuximab vedotin may be effective. Early identification of transformation can guide timely management changes and potentially improve patient outcomes. Awareness of this rare but potentially aggressive progression of MF is vital for dermatologists and pathologists to ensure accurate diagnoses and optimal patient care.