T‐cell chronic lymphocytic leukemia or small‐cell variant of T‐cell prolymphocytic leukemia: a historical perspective and search for consensus
There is a rich history behind the extinct entity ‘T‐cell chronic lymphocytic leukemia (T‐CLL)’ and the now‐established replacement, small‐cell variant of T‐cell prolymphocytic leukemia (T‐PLL‐sv). Herein, we review the history of the events, observations, and discussions that led to this replacement. We also provide a systematic analysis of all previously reported cases of T‐PLL‐sv as well as our four new additional cases. Despite the higher frequency of a normal karyotype and perhaps an overrepresented CD4−CD8− immunophenotype among these patients (compared to T‐PLL in general) as well as bland morphology (that makes them superficially appear more similar to B‐CLL), we argue that the current World Health Organization (WHO)‐based classification as T‐PLL‐sv is adequate and should continue for the time being. Morphologically, T‐PLL‐sv represents approximately one‐fifth of all T‐PLL cases. However, morphology alone does not determine the clinical course and should not be the basis for clinical decision making and prognostication. We propose a clonal evolution model in which mature T‐cell leukemias classified in the past as T‐CLL are perhaps T‐PLL diagnosed early in the course of the disease. Future research using next‐generation sequencing, comparative genomic hybridization, and molecular array studies, including serial analyses of individual cases over time, is needed to better identify this rarely diagnosed, inherently controversial form of T‐cell leukemia.
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