Deletion of the 5' abl region in Philadelphia chromosome-positive chronic myeloid leukemia

Nilotinib versus dasatinib as second-line therapy in patients with Philadelphia chromosome-positive chronic myeloid leukemia in chronic phase who are resistant or intolerant to imatinib: a cost-effectiveness analysis based on real-world data

OBJECTIVE

To evaluate the cost-effectiveness of second-line nilotinib vs dasatinib among patients with Philadelphia chromosome-positive chronic myeloid leukemia in chronic phase (Ph+ CML-CP) who are resistant or intolerant to imatinib, from a US third-party perspective.

METHODS

A lifetime partitioned survival model was developed to compare the costs and effectiveness of nilotinib vs dasatinib, which included four health states: CP on treatment, CP post-discontinuation, progressive disease (accelerated phase [AP] or blast crisis [BC]), and death. Time on treatment, progression-free survival, and overall survival of nilotinib and dasatinib were estimated using real-world comparative effectiveness data. Parametric survival models were used to extrapolate outcomes beyond the study period. Drug treatment costs, medical costs, and adverse event costs were obtained from the literature and publicly available databases. Utilities of health states were derived from the literature. Incremental cost-effectiveness ratios, including incremental cost per life-year (LY) gained and incremental cost per quality-adjusted life-year (QALY) gained, were estimated comparing nilotinib and dasatinib. Deterministic sensitivity analyses were performed by varying patient characteristics, cost, and utility inputs.

RESULTS

Over a lifetime horizon, nilotinib-treated patients were associated with 11.7 LYs, 9.1 QALYs, and a total cost of $1,409,466, while dasatinib-treated patients were associated with 9.5 LYs, 7.3 QALYs, and a total cost of $1,422,122. In comparison with dasatinib, nilotinib was associated with better health outcomes (by 2.2 LYs and 1.9 QALYs) and lower total costs (by $12,655). Deterministic sensitivity analysis results showed consistent findings in most scenarios.

LIMITATIONS

In the absence of long-term real-world data, the lifetime projection could not be validated.

CONCLUSIONS

Compared with dasatinib, second-line nilotinib was associated with better life expectancy, better quality-of-life, and lower costs among patients with Ph+ CML-CP who were resistant or intolerant to imatinib.

Cytogenetic and molecular characteristics of 25 Chilean patients with a variant Ph translocation

Chronic myeloid leukemia (CML) is characterized by the presence of the Philadelphia chromosome (Ph), which results from a balanced translocation between chromosomes 9 and 22, the t(9;22)(q34;q11.2). In 5-10% of the cases, variants of the Ph (vPh) are detected, involving various breakpoints in addition to 9q34 and 22q11.2. Deletions on the der(9) and der(22) can be detected in approximately 10-15% of CML patients. The frequency of a deletion of the der(9) in vPh CML is variable. Most studies have shown high frequencies (30-45%) in this subgroup. We report the cytogenetic evaluation of 25 vPh cases, which represents 6.8% of the CML cases diagnosed at one institution in 20 years. The breakpoints of the partners of the vPh in our patients agree with those reported previously, except for a novel 18q23. We found a low incidence of deletions of the der(9) (10%) and der(22) (5%) in these patients, contrasting with several reports in the literature. This finding may reflect the extensive spectrum of aberrations in vPh, and the possibility that a considerable group of these aberrations may not affect the genetic stability of 5'ABL1 and 3'BCR. Epidemiologic differences may also exist and could explain our results. These differences would require further investigation.

Deletion size characterization of der(9) deletions in Philadelphia-positive chronic myeloid leukemia

About 95% of the CML patients with chronic myeloid leukemia (CML) have a Philadelphia chromosome resulting from a reciprocal translocation between bands 9q34 and 22q11.2 that juxtaposes the 3' region of the ABL gene to the 5' region of BCR. Over the past few years, submicroscopic deletions due to the loss of sequences proximal to chromosome 9 breakpoint or distal to chromosome 22 breakpoint have been found using fluorescence in situ hybridization (FISH). Among 150 CML bone marrow samples analyzed by molecular cytogenetics in our laboratory, 11 had a der(9) deletion detectable by FISH (deletion of the 5'ABL region and 3'BCR region in 10 samples and deletion of the 5'ABL region solely in 1 sample). To delineate the size of the deletions, FISH mapping was performed using 22 bacterial artificial chromosomes (BACs), 11 on either side of the breakpoints, the mean distance between BACs being 0.5 Mb. The deletion size of the 5'ABL region on the der(9) extended from 2 to 5 Mb, the minimal deletion size being localized between BACs RP11-101E3 and RP11-83J21. In two patients, the deletion size of the 3'BCR region was about 500 kb (between RP11-80O7 and RP11-681C06). The poor prognosis associated with these deletions was postulated by several workers to be explained by haploinsufficiency of a tumor suppressor gene. However, in our cases, the hypothetical deletion of one or more tumor suppressor genes is not sufficient to explain the poor response to interferon therapy, but the good response to imatinib treatment. We think that there could be one or more genes coding for interferon receptors or for proteins acting directly or indirectly with these receptors in the deleted regions.

Deletions of the 3′ BCR and 5′ ABL regions in patients with Philadelphia-positive chronic myeloid leukemia: a one-step process occurring in about 10% of the cases without any evidence of genetic instability in the target cells

Deletions of the 5'ABL region adjacent to the t(9;22)(q34;q11) have recently been reported in 8-32.7% of patients with chronic myeloid leukemia (CML). The deletions were visualized with fluorescence in situ hybridization using, in the majority of the cases, the Vysis LSI BCR/ABL ES (extra signal) probe. In our series, 10 of 99 CML patients (10.1%) were characterized by a 5'ABL deletion. We show that 3'BCR losses are observed in nearly all the cases with 5'ABL deletions. Moreover, the different genetic events (Philadelphia chromosome formation; 5'ABL and 3'BCR deletions) occur simultaneously in a one-step process without any evidence for genetic instability in the target bone marrow cells.

Contribution of fluorescence in situ hybridization analyses to the characterization of masked and complex Philadelphia chromosome translocations in chronic myelocytic leukemia

Bone marrow samples from 112 patients with chronic myelocytic leukemia were investigated using cytogenetic methods. Fluorescent in situ hybridization (FISH) with whole-chromosome paints and BCR-ABL probes was used to confirm and/or complete the banding findings when a variant or a masked Philadelphia chromosome (Ph) translocation was found. Eight variant Ph translocations were identified. Three-way Ph translocations were found in seven patients. Chromosome 4 was involved in two of these cases and chromosomes 3, 11, 14, 17, and 16 in one case each; in the patient with chromosome 16 involvement, a ring of the translocated chromosome 9 was identified, that is r(9)t(9;16;22). The eighth patient had a five-way Ph translocation: t(2;9;16;22;22). The BCR-ABL fusion gene was detected on the Ph chromosome in all eight cases; two cases presented also a deletion of the 5' ABL region on the derivative chromosome 9. In the five-way translocation, the 3' DNA sequence of the ABL oncogene was fused with the 5' DNA sequence of the BCR gene on the Ph chromosome and the 5' end of ABL was inserted into the other chromosome 22. A masked Ph chromosome was identified in one of the 112 patients; it involved the insertion of the 3' ABL into BCR on an apparently normal chromosome 22, resulting in the BCR-ABL fusion gene. In conclusion, FISH analyses allowed not only a more accurate characterization of complex Ph translocations with subtle abnormalities and the identification of cryptic rearrangements, but also the recognition of deletion of the 5' ABL region, which could carry with it a poor prognosis.