STAT3 and myeloid leukemia: It may also be noteworthy in the present context that the faster migrating STAT proteins may turn out to be truncated STAT proteins which were previously found to be produced by myeloid leukemia cells where a truncated isoform of STAT3 (e.g. STAT3β) [20] was eventually traced to the activity of a serine-dependent protease produced by these cells acting on STAT3α [21].