Mature T-Cell and Natural Killer–Cell Leukemias

Abstract This chapter focuses on the mature or peripheral T-cell neoplasms that tend to manifest clinically as leukemia. These include mainly T-cell large granular lymphocytic leukemia, Sezary syndrome and mycosis fungoides, adult T-cell leukemia-lymphoma, T-cell prolymphocytic leukemia, and aggressive natural killer (NK)-cell leukemia. Mention is made of NK-cell large granular lymphocytic leukemia (chronic NK-cell lymphocytosis), leukemic phase of peripheral T-cell lymphomas, and lymphocytic variant hypereosinophilic syndromes. Distinction of these entities depends largely on morphologic examination of peripheral blood films and immunophenotypic analysis of the tumor cell population described herein and on correlation with clinical features. T-cell receptor gene rearrangement studies and cytogenetic analysis have a role in their diagnosis, but to a lesser extent than the aforementioned findings. These T-cell lymphoproliferations are mostly diseases of adults, and they have widely varying prognoses between each other making appropriate diagnosis critical for proper clinical management.