Monitoring Response to Imatinib By Fluorescence In Situ Hibridization (FISH) and Real-Time Quantitative Polymerase Chain Reaction (RQ-PCR) In Chronic Myeloid Leukemia (CML) Patients (PTS) In Chronic Phase (CP): Experience of Argentina and Uruguay

Reviewer: Neha Vapiwala, MD
Abramson Cancer Center of the University of Pennsylvania
Last Modified: March 21, 2007

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Presenter: Pavlovsky, C
Presenter's Affiliation: FUNDALEU (Argentina)
Type of Session: Scientific

Background

The impressive efficacy of imatinib in CML is well-established and is correlated directly with transcription levels of its target, bcr-abl. Higher doses of imatinib are indicated in pts with rising levels of bcr/abl transcripts. RQ-PCR is considered to be the optimal method for determining levels of bcr/abl transcripts in pts with CML. Furthermore, the degree of reduction of total leukemia cell mass by imatinib as measured by FISH and RQ-PCR correlates with progression-free survival. This study was undertaken to determine the potential of RQ-PCR to predict ongoing pt response to imatinib based on the duration of complete cytogenetic remission (CCyR).

Materials and Methods

  • Prospective, multicentric study initiated in November 2005
  • A total of 177 pts were enrolled, 164 from Argentina, 13 fron Uruguay
  • Of these, 154 pts with CP-CML presently in CCyR and treated with 400 mg/d imatinib were included.
  • Pts were divided into two groups based on their 1st line treatments :
    • IFN/Cytarabine, 83 pts (51%)
    • Imatinib, 77 pts (49%)
  • At baseline, all pts were studied by both FISH and RQ-PCR
  • Follow up RQ-PCR was then performed at 6, 12, and 18 months
  • Imatinib median duration was 26 months (range 6-64)
  • All pts (100%) completed the first and second evaluations, whereas only 37% had their third evaluation as of March 2007.

Results

  • Median f/u = 37 months
  • Patient demographics:
    • Median age = 51
    • Male = 64%
    • Sokal score risk category: 57% low, 30& intermediate, 19% high
  • First FISH evaluation showed:
    87% pts with 0% bcr/abl(+) cells = FISH neg
    13% pts with 0.1-5% bcr/abl(+) cells = FISH pos
  • Molecular responses (MR) in 160 pts were:
    Complete (CMR), >4 Log Reduction: 23%
    Major (MaMR), >3 Log Reduction:17%
    Minor (MiMR), >2 Log Red: 34%
    Minor, < 2 Log Red: 15%
    Nule (NuMR),< 1 Log Red: 11%
  • No significant differences in MaMR and CMR were observed between pts with < 12 months vs. > 24 months of imatinib therapy (42% vs 47%).
  • Follow-up in 68 pts (at 6 months) showed: better MR in 13% pts, invariable in 68% pts , worse in 19% pts

Author's Conclusions

  • In this ongoing study, 87% CML pts were FISH (-), of which 78% had maintained or improved molecular responses:
  • 42% achieved >3 Log Red MR (CMR or MaMR) at baseline, 42% at second evaluation (at 6 mos), and 56% at third evaluation (at 12 mos)
  • Overall, 78% of pts who were FISH (-) had improved or maintained MR on Imatinib therapy at 12 months of follow up.
  • The MRs did not vary significantly based on Sokol risk group classification.
  • All pts are presently still in hematologic remission.

Clinical/Scientific Implications

This study presents data that provide a very nice correlation between clinical, molecular, and cytogenetic parameters in the treatment of chrnic-phase CML with the novel bcr-abl targeting agent, Imatininb. In the study population reported here, an overall 78% of pts who were FISH (-) had improved or maintained MR on Imatinib therapy at 12 months of follow up. Furthermore, all pts reported here continue to be in complete remission, both cytogenetically and hematologically. Thus it appears that RQ-PCR is indeed a useful indicator of ongoing response to long-term Imatinib therapy in chronic phase CML pts. In this era of long-term Imatinib treatment, additional studies are warranted to evaluate the identification and characterization of patients destined to be late-progressors, as well as to better understand the longer-term adverse effects profile of imatinib in this population.