Cytogenetics is one of the most important prognostic factors in acute myeloid leukemia (AML). Breems et al., based on banding techniques (BT), have identified a monosomal karyotype (MK) to be associated with particularly poor survival. MK is defined by the presence of an autosomal monosomy in conjunction with at least one other autosomal monosomy or structural abnormality. However, classical BT may be not sufficient to confirm the “real” loss of a particular chromosome, especially in patients with complex karyotype (≥ 3 or ≥ 5 separate abnormalities) where parts of „missing” chromosomes could be involved in structural aberrations such as: additions, derivative chromosomes, rings, marker chromosomes and dicentrics. Molecular cytogenetic techniques, such as FISH, could be useful to verify if observed monosomy was “total” (loss of a complete chromosome) or “partial” (loss of only a part of chromosome including centromere).
The aim of our study was to assess if the type of monosomy (total or partial), defined using FISH influences the prognosis of AML patients with MK.
Materials and methods: Fifty newly diagnosed AML patients with MK, treated between January 2005 and January 2011 with PALG AML1/2004 and AML2/2004 protocols were included into the study. Cytogenetic analysis was performed on metaphases from bone marrow aspirates taken at diagnosis using standard BT. Karyotypes were centrally reviewed by two independent cytogeneticists and reported in accordance with the ISCN. In 41 cases FISH was performed with painting probes and in justified cases additionally with satellite probes and locus-specific probes to assess the type of monosomy. In 9 patients no confirmation by FISH was needed.
In 8/50 (16%) patients FISH verification proved the complex, but not monosomal (total or partial) karyotype. These patients were excluded from further study. The median age of 42 evaluable patients was 58 years (range 20–71 years). There were 26 males and 16 females. Twenty three (55%) patients received intensive induction chemotherapy according to PALG protocols (Holowiecki et al. Leukemia 2004), 8 patients - low dose cytarabine and 11 patients with high frailty index received treatment with hydroxyurea (n=9), and best supportive care (n=2).
In 38/42 (90.5%) analyzed cases with MK abnormalities were complex. In all but one ≥5 separate aberrations were present. In 27/42 (64.3%) cases a total monosomy was confirmed by FISH (group A) and in 15/42 (35.7%) cases FISH revealed a monosomy to be the partial one (group B). Both groups A and B were comparable in terms of age, sex, immunophenotype and factors associated with tumor mass (leukemic bone marrow infiltration, WBC and peripheral blood blast count, as well as LDH activity). There was also no difference in the proportion of intensive and non-intensive treatment strategies between both groups. Six (26,1%) of intensively treated patients achieved complete remission (CR). The CR rate in patients with partial monosomy (40%) was higher than in total monosomy group (15,4%), however the difference was not significant (p=0.19; Fisher's exact test). The median overall survival (OS) for all evaluable patients was 66 days (range 1–659 days) and the probability of OS at 1 yr was 14% (95% CI 4–23%). Total monosomy was the only factor associated with decreased probability of OS both in univariate (p=0.036) (Fig. 1) and multivariate (p=0.037) analyses in AML patients with MK.
Additionally, in patients with total monosomy the frequency of distinct monosomies was analyzed. The most frequent monosomies were monosomy 7 (n=13; 48%) and monosomy 18 (n=10; 37%). Other total monosomies included: monosomy 17 (n=3; 11%), monosomy 16 (n=2; 7%) and others (n=4). We did not observe any total monosomy 5.
Our results indicate for the first time that partial monosomy is associated with significantly better OS than total monosomy in high risk AML with MK and provide further evidence for the heterogeneity of this defined cytogenetic group. These data also clearly demonstrate an important role of FISH method for precise evaluation of complex karyotype, which results in correct classification within MK group, as well as in adequate description of monosomy type.
Wierzbowska:Genzyme: Membership on an entity's Board of Directors or advisory committees. Dmoszynska:Roche: Honoraria; Mundipharma:.
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