Cutaneous lymphoma and important differential diagnoses: emphasis on cases with a cytotoxic phenotype

Cutaneous T-cell lymphomas with a cytotoxic phenotype are a heterogeneous collection of neoplasms with varied presentation and behaviour. Clinical course ranges from self-limiting disease associated with spontaneously resolving lesions, to aggressive, rapidly progressing neoplasms that are almost uniformly fatal despite therapeutic intervention. Included in this group are CD8-positive variants of mycosis fungoides and lymphomatoid papulosis, as well as neoplasms in which identification of a cytotoxic phenotype is a diagnostic criterion. Examples of the latter are primary cutaneous CD8-positive aggressive epidermotropic T-cell lymphoma, primary cutaneous γ/δ T-cell lymphoma, subcutaneous panniculitis-like T-cell lymphoma, extranodal NK/T-cell lymphoma, nasal type and primary cutaneous acral CD8-positive T-cell lymphoma. Recognition of these entities is therefore of paramount importance but remains problematic. In large part this is because many display overlapping and often indistinguishable pathological features. This review highlights microscopic appearances that may assist in diagnosis whilst stressing the central role played by clinical correlation.