Context: Primary cutaneous CD4⁺ small/medium T-cell lymphoma is a provisional and controversial entity with a broad differential diagnosis. Despite being an uncommon lymphoma, it is a frequent diagnostic consideration in cutaneous biopsies with a dense lymphoid infiltrate because it shows overlapping features with reactive lymphoid hyperplasia (pseudolymphoma) and a variety of other primary cutaneous and systemic lymphomas. However, proper classification of this process is important for determining patient prognosis and treatment options.
Objective: To review the clinical, morphologic, immunophenotypic, and genetic features of primary cutaneous CD4⁺ small/medium T-cell lymphoma and contrast those features with entities in the differential diagnosis.
Data sources: Applicable literature will be reviewed with emphasis on current controversies and distinguishing characteristics.
Conclusions: Although many consider primary cutaneous CD4⁺ small/medium T-cell lymphoma to be indistinguishable from reactive lymphoid hyperplasia/pseudolymphoma, it can be differentiated from other primary cutaneous and systemic lymphomas. Patients with solitary lesions of primary cutaneous CD4⁺ small/medium T-cell lymphoma generally have an excellent prognosis. Nevertheless, a subset of patients who have been reported to meet criteria for this lymphoma have followed a more-aggressive course; however, those patients show some differing clinical, morphologic, and immunophenotypic features.