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Primary cutaneous lymphomas other than mycosis fungoides.

Primary cutaneous lymphomas present in and are confined to the skin with no evidence of extracutaneous disease. The skin is the second most common extranodal site involved by primary lymphoma; 50% are mycosis fungoides (MF)-type cutaneous T-cell lymphoma, with the remainder being peripheral T-cell lymphoma (25%) and B-cell lymphoma (25%). The diagnosis of non-MF primary cutaneous lymphomas differs from that of nodal lymphomas: (1) presentation in the skin more often predicts outcome than histology, (2) immunophenotyping and immunogenotyping studies show differences in chromosomal translocations, cell-surface antigen expression (T-cell receptor [TCR] and immunoglobulin [Ig] heavy and light chains), and oncogene expression, (3) involvement of structural compartments of the skin (epidermis, periadnexal or adventitial dermis, interstitial dermis, and subcutis) aids differential diagnosis in place of nodal architecture, and (4) cytokine and extracellular matrix environments may influence behavior of cutaneous lymphomas. Diagnosis often requires coordinated evaluation of clinical history, immunohistochemistry on paraffin and frozen sections of skin biopsies, and molecular analysis. Classification of primary cutaneous lymphomas by a combined histologic type and clinical behavior is useful.