A new classification of clinical stages of adult T-cell leukemia based on prognosis of the disease.

Adult T-cell leukemia (ATL) has been classified into three clinical subtypes: acute, chronic, and smoldering type. However, these clinical subtypes of ATL do not always correlate with prognosis. We propose a new criterion for classification of clinical stages of ATL, based on the expression of Ki-67 antigen in peripheral blood T lymphocytes. We analyzed Ki-67 antigen expression in 45 ATL patients, classified as 18 acute, 17 chronic, and ten smoldering type. We found that in 23 patients with more than 18% Ki-67 antigen-positive T cells, the disease progressed very aggressively, and all patients died within 1 year (mean survival, 105 days). This group included 15 of 16 patients classified as 'acute', seven of 15 patients classified as 'chronic', and one of nine patients classified as 'smoldering' type. In contrast, 15 out of 17 patients with less than 18% Ki-67 antigen-positive T cells were still alive at the end of the study, with a mean survival of 750 days. Only two patients died in this group, and after a very long survival (599 and 978 days, respectively). We therefore propose the following new classification for ATL: (i) Aggressive ATL; percentage of Ki-67 antigen-positive cells more than 18% in peripheral blood T lymphocytes, (ii) Stable ATL; percentage less than 18%. This classification strongly correlates with the prognosis of patients with ATL.