Recommendations for assessment and definitions of response and relapse in CML: of the IBMTR

Bennett1 and Virchow2 first described chronic myeloid leukemia (CML) in 1845. Early therapy (Fowler solutions or radiotherapy) produced hematologic improvement, but there were no formal attempts to quantify or qualify responses.3-6 Formal definitions of remission and relapse were first used in acute leukemia studies during the late 1950s.7 The introduction of busulfan in 19538,9 and hydroxyurea in 196610

and the design and conduct of trials comparing these agents with each other and with other therapies led to a need for standardized response criteria for CML.9,11-13

The original response criteria for CML related exclusively to clinical symptoms, peripheral blood morphology, and spleen

size.8-13 The discovery of the Philadelphia chromosome (Ph) in 196014 and further work elucidating its molecular abnormalities made apparent the importance of translocation of genetic material between chromosomes 9 and 22 and the resultant BCR/ABL protein in disease pathogenesis.15