Impact of the Normalized Copy Number of <i>BCR-ABL</i> Transcript upon Diagnosis on Prognosis in CML Patients Treated with Imatinib-Mesylate

doi:10.4236/ojbd.2011.12004

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Open Journal of Bloo d Di seases, 2011, 1, 12-14

doi:10.4236/ojbd.2011.12004 Published Online December 2011 (http://www.SciRP.org/journal/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.

Email: [email protected]

Received September 26th, 2011; revised October 30th, 2011; accepted November 16th, 2011.

ABSTRACT

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

treatment.

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

Software.

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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