WHO Classification of Cutaneous Lymphomas

Overview / Definition Cutaneous lymphomas encompass a diverse group of lymphoproliferative disorders primarily affecting the skin. The World Health Organization (WHO) classification system provides a comprehensive framework for categorizing cutaneous lymphomas into various subtypes, enabling accurate diagnosis and appropriate management. Epidemiology Cutaneous lymphomas are relatively rare, comprising approximately 4% of all lymphomas. The incidence varies by subtype: Mycosis fungoides (MF) is the most prevalent, accounting for about 50% of cases. Sezary syndrome, a leukemic form of MF, is less common but significant. Other T-cell lymphomas, such as primary cutaneous anaplastic large cell lymphoma (PC-ALCL), represent 10-20% of cases. Pathophysiology / Mechanism Cutaneous lymphomas arise from neoplastic transformations of lymphocytes, with the majority being T-cell lymphomas. The pathogenesis involves: Genetic mutations leading to uncontrolled cell proliferation. Environmental factors, including UV exposure and viral infections (e.g., HTLV-1). Immune dysregulation contributing to the clinical manifestations. Clinical Presentation Clinical features vary significantly based on the specific subtype of cutaneous lymphoma: Mycosis fungoides: Presents as patches, plaques, or tumors, often resembling eczema or psoriasis. Sezary syndrome: Characterized by erythroderma, lymphadenopathy, and circulating atypical T-cells. Primary cutaneous anaplastic large cell lymphoma: Typically appears as solitary or multiple nodules. Diagnosis / Workup Diagnosis relies on a combination of clinical evaluation and histopathological examination: Skin biopsy: Essential for confirming the diagnosis and determining the subtype. Immunohistochemistry: Used to characterize the lymphocyte lineage and rule out other conditions. Cytogenetic studies: May be performed to identify specific chromosomal abnormalities. Treatment / Management Management strategies are tailored based on the specific subtype a