BCR-ABL messenger RNA levels continue to decline in patients with chronic phase chronic myeloid leukemia treated with imatinib for more than 5 years and approximately half of all first-line treated patients have stable undetectable BCR-ABL using strict sensitivity criteria.
OBJECTIVE
In the first years of imatinib treatment, BCR-ABL remained detectable in all but a small minority of patients with chronic myeloid leukemia. We determined whether BCR-ABL continues to decline with longer imatinib exposure and the incidence and consequence of undetectable BCR-ABL.


METHODS
BCR-ABL levels were measured in a subset of 53 imatinib-treated IRIS trial patients for up to 7 years (29 first-line, 24 second-line). Levels were deemed undetectable using strict PCR sensitivity criteria.


RESULTS
By 18 months, the majority achieved a 3-log reduction [major molecular response (MMR)]. BCR-ABL continued to decline but at a slower rate (median time to 4-log reduction and undetectable BCR-ABL of 45 and 66 months for first-line). The probability of undetectable BCR-ABL increased considerably from 36 to 81 months of first-line imatinib {7% [95% confidence interval (95% CI), 0-17%] versus 52% (95% CI, 32-72%)}. Undetectable BCR-ABL was achieved in 18 of 53 patients and none of these 18 lost MMR after a median follow-up of 33 months. Conversely, MMR was lost in 6 of 22 (27%) patients with sustained detectable BCR-ABL and was associated with BCR-ABL mutations in 3 of 6. Loss of MMR was recently defined as suboptimal imatinib response. There was no difference in the probability of achieving molecular responses between first- and second-line patients but first-line had a significantly higher probability of maintaining MMR [P = 0.03; 96% (95% CI, 88-100%) versus 71% (95% CI, 48-93%)].


CONCLUSIONS
With prolonged therapy, BCR-ABL continued to decline in most patients and undetectable BCR-ABL was no longer a rare event. Loss of MMR was only observed in patients with sustained detectable BCR-ABL.
Institute of Medical and Veterinary Science, Adelaide, Australia. susan.branford@imvs.sa.gov.au
Susan
S
Branford
John F
JF
Seymour
Andrew
A
Grigg
Chris
C
Arthur
Zbigniew
Z
Rudzki
Kevin
K
Lynch
Timothy
T
Hughes
D000970:Antineoplastic Agents / Q000627:therapeutic use; D001549:Benzamides; D002986:Clinical Trials as Topic; D016044:Fusion Proteins, bcr-abl / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism*; D015466:Leukemia, Myeloid, Chronic-Phase / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010879:Piperazines / Q000627:therapeutic use*; D016133:Polymerase Chain Reaction / Q000379:methods; D011743:Pyrimidines / Q000627:therapeutic use*; D012333:RNA, Messenger / Q000378:metabolism*; D012074:Remission Induction; D012680:Sensitivity and Specificity
D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D012333:RNA, Messenger; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl