Mycosis fungoides and Sézary syndrome: clinical, immunological and molecular distinctions that suggest two different diseases

Although mycosis fungoides and Sézary syndrome are presently defined by the WHO/European Organization for Research and Treatment of Cancer criteria as two distinct subtypes of cutaneous T-cell lymphoma, the two diseases present with some overlapping clinical and pathological features and share the same staging system. Advances in understanding the roles and immunologic features of different subsets of T helper cells have allowed researchers to segregate mycosis fungoides and Sézary syndrome with more precision, suggesting that these diseases, despite some similarities, arise from distinct T-cell subsets. New evidence acquired from recent studies in genetics and molecular signaling pathways has contributed to a more comprehensive understanding of these two disease entities, supporting this theory. The purpose here is to survey recent advances in the biological origin, immunophenotype, genetics and molecular profiles of mycosis fungoides and Sézary syndrome, leading to a greater understanding of the differences between the two entities that will allow for improved diagnosis, prognosis and treatment.