Open Journal of Bloo d Di seases, 2011, 1, 12-14
doi:10.4236/ojbd.2011.12004 Published Online December 2011 (
Copyright © 2011 SciRes. OJBD
Impact of the Normalized Copy Number of
BCR-ABL Transcript upon Diagnosis on Prognosis
in CML Patients Treated with Imatinib-Mesylate
Christophe Martinaud1, Aurélie Mayet2, Sophie Bousquet3, Nathalie Beaufils4, Jean Gabert4,
Sophie Raynaud3, Marie-Joelle Mozziconacci5
1Fédération des Laboratoires, HIA Percy, Clamart, France; 2Département d'Epidémiologie et de Santé Publique, Ecole du Val-de-
Grâce, Paris, France; 3Laboratoire d’Onco-hématologie, Hôpital Pasteur, CHU de Nice, Nice, France; 4Laboratoire de Biologie Mo-
léculaire, APHM Nord, Marseille, France; 5Laboratoire de Biologie Moléculaire, Département de Biopathologie, Institut Paoli Cal-
mettes, Marseille, France.
Received September 26th, 2011; revised October 30th, 2011; accepted November 16th, 2011.
Quantification of the BCR-ABL transcrip t is recommended to follo w-up CML pa tien ts treated by imatin ib mesylate (IM).
Results are expressed as a normalized copy number (NCN) of BCR-ABL. We studied a cohort of 98 CML patients under
IM as a first treatment and monitored by RQ-PCR after 12, 18 and 24 months according to the European LeukemiaNet
recommendations. Our results support th e hypothesis of an independen t correlation between BCR-ABL NCN at diagno-
sis and major molecular response at 18 and 24 months in an inverse relation ship. We also high lighted the possibility to
use the NCN at diagnosis as a wa rning at diagnosis, and may be useful to identify patients who cou ld benefit of a more
rigorous follow-up.
Keywords: Chronic Myeloid Leukemia, RQ-PCR, Normalized Copy Number, BCR-ABL
1. Introduction
Chronic myeloid leukemia (CML) is a clonal disease of
the hematopoietic stem cell characterized by a recipro-
cal translocation t(9;22)(q34; q11) that fuses the ABL
and BCR genes located on 9q34 and 22q11 respec-
tively. Imatinib mesylate (IM), a tyrosine kinase in-
hibitor, blocks the kinase activity of BCR-ABL and
induces complete cytogenetic response in a majority of
the patients [1,2]. Quantification of the BCR-ABL
transcript by quantitative reverse transcriptase poly-
merase chain reaction (RQ-PCR) is recommended for
accurate follow-up of treated CML patients. Results are
expressed as a ratio of BCR-ABL on a control gene
(normalized copy number: NCN). Based on the IRIS
(International Randomized study of Interferon and
STI571) trial, the concept of measuring a log10 reduc-
tion in BCR-ABL transcript from a standardized base-
line value has been proposed [3]. The standardized
baseline value, defined as the median of NCN for 30
untreated patients from the same laboratory, is taken to
represent the BCR-ABL transcript level of 100% tumor
cell burden, and the major molecular response (MMR)
is defined as a 3-log or more reduction of the baseline
value (0.1%). The IRIS study demonstrated that pa-
tients who achieved a MMR in the first year had no
disease progression at 5 years [1]. Lack of MMR at 18
months is qualified as suboptimal response and might
lead to a dose escalation of IM or to the shift to a sec-
ond generation tyrosine kinase inhibitor [4,5]. It should
be very important to evaluate the prognostic and the
probability of achievement of MMR since the diagno-
sis to allow a better and an earlier adaptation of the
2. Patients and Methods
In order to evaluate the prognostic impact of BCR-ABL
NCN at diagnosis on the achievement of MMR as de-
fined by the IRIS study, we compared the NCN of
MBCR-ABL transcript in newly diagnosed CML patients
before treatment as detected in 3 laboratories in South of
France (Marseille APHM, Marseille IPC and Nice) and
analysed the data of a cohort of 98 CML patients treated
Impact of the Normalized Copy Number of BCR-ABL Transcript upon Diagnosis on Prognosis 13
in CML Patients Treated with Imatinib-Mesylate
by IM 400 mg/day as a first line treatment, and moni-
tored by RQ-PCR for BCR-ABL transcript after 12, 18
and 24 months of treatment in the 3 laboratories. RQ-
PCRs were performed on peripheral blood cells accord-
ing to the European Leukemia Net recommendations [6]
on 3 machines: MX3000 (Stratagen), TaqMan 7900 and
TaqMan 7500 (Applied Biosystems) respectively. Ac-
cording to Hughes et al. [6], the control gene was ABL
and the standardized baseline values were 92, 125 and
110 copies of MBCR-ABL/102 copies of ABL in the 3
laboratories respectively. Results were referenced to sets
of plasmids for ABL and MBCR-ABL (Ipsogen, Mar-
seille-France). Median ABL cycle thresholds (Ct) was
25.03 (standard deviation: 1.85) and the median ABL
copy number was up to 20,000. 64% of patients were
male, median age at diagnosis was 58 years (range 1-85).
Sokal risk score was available for 65 patients: 25% low
risk (n = 16), 48% intermediate risk (n = 31), and 28%
high risk (n = 18). Data were analysed using SAS 9.1
3. Results and Discussion
At diagnosis, patients were separated in two groups, de-
pending on whether the NCN of BCR-ABL transcript at
diagnosis was above (group A, n = 52 patients) or under
(group B, n = 46) the standardized baseline value of each
laboratory. At 12 months, 80 patients were eligible for
analysis: 21 patients from group A (47%) and 22 from
group B (63%) achieved a MMR. No significant relation
between NCN at diagnosis and MMR at 12 months was
found (Chi-square test).
At 18 months, 98 patients were eligible for analysis:
25 patients from group A (48%) and 35 from group B
(76%) achieved a MMR. On univariate analysis, a NCN
at diagnosis above the standardized baseline value was
significantly associated with a 4 fold higher risk (odds
ratio (OR) = 0.2 [0.1 - 0.7]) of non MMR at 18 months (p
= 0.001). The mean NCN at diagnosis was significantly
lower in patients who achieved a MMR at 18 month
compared with non-responders (13 vs 21 copies of
MBCR-ABL/102 copies of ABL, p = 0.02 ANOVA).
Moreover, distribution of Sokal risk showed no differ-
ence between patients who had a NCN at diagnosis
above the standardized baseline and those who had a
NCN at diagnosis under this baseline, attesting to an
homogenous repartition of Sokal score between the two
groups. We also showed that there were no difference for
the mean of NCN at diagnosis between the three groups
of Sokal (low, intermediary and high) i.e. 22, 18 and 15
copies of MBCR-ABL/102 copies of ABL (p = 0.6 vari-
ance analysis). Altogether, our analysis account for an
independence of NCN at diagnosis and Sokal score in the
prediction of the obtention of a MMR at 18 months.
At 24 months, 86 patients were eligible for analysis:
54 (63%) achieved a MMR: 26 from group 1 (55%) and
28 from group B (72%). A significant relation between
NCN at diagnosis and MMR at 24 months was still as-
sessed (chi-square test, p = 0.05).
Finally, as a study demonstrated the impact of the
12-month cytogenetic response on the overall survival
and the probability to achieve a complete cytogenetic
response (CCyR) [7], we compared the NCN values at
diagnosis with the cytogenetic responses at 12 months.
These data were available for 34 patients. We compared
the distribution of CCyR in each subgroup: 33% of pa-
tients with NCN at diagnosis below the standardized
baseline failed to obtain a CCyR, versus 38% in the NCN
above it. No significant difference of distribution was
observed between the groups in terms of CCyR at 12
months. We are aware that an analysis taking CCyR at 3
months could be relevant [5], though this data was not
available at the time of the study.
4. Conclusions
Our results support the hypothesis of an independent
correlation between NCN of BCR-ABL transcript at di-
agnosis and MMR at 18 months, sustained at 24 months.
This observation has to be reinforced by a ROC analysis
of a larger population. We sho wed that this correlation is
independent with the Sokal score. This can be of major
importance since Sokal, or Hasford scores, are currently
the only prognostic factors at diagnosis [8] though they
were established before the tyrosine kinase inhibitors era.
At present, several therapeutic options are available to
treat CML patients and the goal is to identify as soon as
possible patients who might resist to imatinib and could
benefit of alternative therapeutic strategies.
Our data suggest that a high NCN at diagnosis should
be considered as a warning and may identify patients
who could benefit of a straighter follow-up. If our results
are confirmed on a larger series, they could be part of a
new composite prognostic score available at diagnosis
and in combination with the use of international conver-
sion factors improve current scoring systems.
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Copyright © 2011 SciRes. OJBD
Impact of the Normalized Copy Number of BCR-ABL Transcript upon Diagnosis on Prognosis
in CML Patients Treated with Imatinib-Mesylate
Copyright © 2011 SciRes. OJBD
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