Alistair Robson, BSc (Hons), MB, ChB, MRCPath, DipRCPath

The diagnosis of cutaneous T-cell lymphoma (CTCL) requires accurate histopathology, including immunocytochemistry, as well as careful clinical appraisal and analysis for T-cell clonality. This paper reviews the key histologic features of mycosis fungoides (MF) and its variants, and of lymphomatoid papulosis (LyP). Mycosis fungoides is an epidermotropic CTCL that evolves through distinct disease stages of patch, plaque, and tumor, often leading to transformation in the final stages. Disease staging is made clinically, and diagnosis may be difficult during the early stages because several common dermatologic conditions share features with MF. Therefore, clinical appraisal plus the presence of characteristic histopathologic features are needed to ensure accurate diagnosis. Clinical information is particularly important in the diagnosis of LyP, as the disease appears malignant histologically, but has a benign clinical course. Several other T-cell lymphomas were defined in a recent classification of these cutaneous lymphomas, and some key features of these disorders are also briefly reviewed.