Landmark Analyses of BCR-ABL Using ES-FISH Early After Start of Imatinib Treatment to Newly Diagnosed CMLcp Patients Predicts Longterm Clinical Outcome.
Authors: Ohm Lotta , Hast Robert , Arvidsson Ingrid , Barbany Gisela , Stenke Leif 
Published: October 2019

Abstract
Abstract 4269

Background
Imatinib (IMA) is recommended as first-line therapy for patients diagnosed with CML in chronic phase (CMLcp). Earlier studies, based particularly on the IRIS trial, have indicated that a favorable long-term clinical outcome to therapy is clearly associated with a reduction of the Ph-pos cell population and of BCR-ABL transcripts, as measured with cytogenetics and qPCR, respectively. We have investigated the response to IMA in a CMLcp cohort treated at our institution and assessed the prognostic value of early and repeated determinations BCR-ABL expression, using both ES-fluorescence in situ hybridization (FISH) and qPCR.

Methods
45 pts with newly diagnosed CMLcp (24M/21F; median age 54 yrs, range 19-87; 5 with 9q del, 5 with variant translocations; Sokal scores 16 LR, 20 IR, 9 HR) were started on IMA (400mg qd) and hematologic, cytogenetic and molecular responses were followed at regular 3-mo intervals. Median IMA treatment time at follow-up was 29 mo (range 9-94). Regular cytogenetic karyotyping (CG) and interphase ES-FISH were performed on bone marrow cells (the latter method by scoring BCR-ABL in at least 500 cells on smear preparations, detection limit 20.2%) while qRT-PCR was performed on peripheral blood leukocyte samples with ABL as control gene. Major molecular response (MMR) was defined as the ratio BCR-ABL/control gene 20.1%.

Results
At diagnosis the pts displayed a median of 100% (range 67-100) Ph-pos metaphases by CG, while ES-FISH revealed BCR-ABL gene expression in a median of 86,2% (range 45,9-97,3) of cells. The response to IMA-treatment during the first 12 mo, displayed in Table I, included CCyR in 80%, MMR in 48% and reduction of FISH-detected BCR-ABL to <1% in 62% of analyzed pts. When first obtaining CCyR (negative CG), patients showed a median
ES-FISH value of 0.27% (range 0 to 7.4%). Comparing pts who did vs. did not achieve CCyR at 12 mo (n= 36 vs. 9) FISH and PCR analyses at 3, 6 and 9 mo showed clear differences between the groups (Table II).
At 24 months from start of IMA, 39 pts were evaluable for response and ‘events‘ (defined according to ELN as any of: death during study treatment, loss of CHR, loss of MCyR, progression to AP/BC or WBC>20). A total of 6 pts showed ‘event‘ (4 AP, 1 BC, 1 loss of CHR; 2 died). Table III provides landmark data related to FISH and PCR levels at 3 time points. Patients with a high remaining BCR-ABL expression were more likely to develop ‘events‘, as compared to those with low expression.

Conclusion
Our single centre data from an unselected CMLcp pat cohort on first-line IMA shows good clinical and molecular responses, well in line with results from the IRIS study. We propose that repeated, longitudinal interphase ES-FISH analyses may provide additional and important prognostic information regarding later targeted clinical endpoints. The method gives reliable information also early during the treatment, at higher disease penetration when PCR may be less reproducible, and can also be performed on peripheral blood samples.

Disclosures:
No relevant conflicts of interest to declare.