Patients with Chronic Phase CML in the IRIS Study Who Receive Imatinib Mesylate (IM) 2nd Line after Prior IFN/Ara-C Have Sustained Complete Cytogenetic and Major Molecular Response Rates Similar to 1st Line IM Patients.
Authors: Kaeda Jaspal , Hochhaus Andreas , Radich Jerald , Branford Susan , So Charlene , Gathmann Insa , Wehrle Elisabeth , Goldman John , Hughes Timothy ,   on Behalf of IRIS Study Group
Published: October 2019

The IRIS study compared IM and interferon+cytarabine (IFN/Ara-C) in patients (pts) with newly diagnosed CML-CP (n=553 per arm). IFN/Ara-C pts. could cross over to IM if they satisfied predetermined criteria for disease, either resistance/refractoriness (=resistance), or intolerance of or reluctance to continue the combination (=lack of resistance). Pts who received IM 1st line or 2nd line who achieved a complete cytogenetic response (CCyR) had BCR-ABL transcript levels measured serially by real-time quantitative PCR (RQ-PCR). Results were expressed as log reduction in BCR-ABL/BCR from a standardized baseline value for untreated pts. Yearly rates of 3 log reduction (Major Molecular Response, MMR) from IM treatment starting date were estimated by multiplying the CCyR rate by the MMR rate in CCyR pts at each time point. Overall, of 553 pts who received 1st line IM 82% achieved CCyR, an estimated 69% during the 1st year (yr) of treatment. Of 359 pts who received 2nd line IM, 80% achieved CCyR, 62% during the 1st yr; rates were lower in pts with resistance than in those without resistance to prior IFN/Ara-C (75% vs 85% overall, p=0.025, 56% vs 68% within first yr, p<0.01). Best observed and estimated molecular responses for CCyR pts. are summarized in the table. The median follow-up for BCR-ABL evaluation on 1st line vs 2nd line IM was 45 and 35 months, respectively.

Molecular response on 1st- and 2nd-line IM in the IRIS study 1st-line IM 2nd-line IM after IFN/Ara-C All pts N = 553 All pts N = 359 Resistance N =174 Lack of resistance N =185 CcyR 454 (82%) 288 (80%) 131 (75%) 157 (85%) Pts with CCyR during treatment and PCR sample(s) N = 401 N = 211 N = 98 N = 113 –≥3 log reduction (MMR) 323 (81%) 154 (73%) 63 (64%) 91 (81%) –≥ 4 log reduction 216 (54%) 92 (44%) 35 (36%) 57 (50%) Estimated % of all pts who achieve CCyR and MMR by – 1 yr 36 24 19 28 – 2 yr 59 38 29 45 – 4 yr 67 67 58 72 – 5 yr 85 82 78 84

Overall response rates were similar between 1st and 2nd line IM pts, although responses in 2nd line IM pts may have occurred more slowly. However, the number of RQ-PCR samples between 1 and 2 yrs of 2nd line IM was limited as samples were not obtained routinely between Jan 2003 and Aug 2004. In pts who achieved CCyR, the estimated 5-yr progression rate to advanced CML phase was 3% for 1st line IM and 4% for 2nd line IM; using the broader definition of progression (including events such as CML-unrelated deaths and loss of MCyR/CHR) the progression rates were 9% and 8% respectively. In both 1st and 2nd line IM pts with CCyR who also achieved MMR, only an estimated 1% progressed to advanced phase within 5 yrs; the estimated broadly defined event rates were 5% and 4% respectively. In summary, for 1st line IM patients with a RQ-PCR follow-up of up to 5 yrs, an estimated 85% achieved MMR at 5 yrs compared with 59% at 2 yrs. Cytogenetic and molecular response rates were similar for 1st line and 2nd line IM pts, primarily due to responses in pts who crossed over for reasons other than resistance or refractoriness. For IM pts the rate of progression to advanced CML phase at 5 yrs was low in those with CCyR and even lower in pts who also achieved MMR.