The Cytogenetic Profile In Lymphoid and Myeloid CML Blast Crisis

In acute leukemias, specific cytogenetic aberrations frequently correlate with myeloid or lymphoid phenotype of blasts and influence risk stratification. In chronic myeloid leukemia (CML) blast crisis (BC) it is not clear whether myeloid or lymphoid phenotype of blasts could be distinguished by specific chromosomal aberrations and have prognostic value. At diagnosis of CML, major route additional cytogenetic aberrations (ACA) like +8, i(17)(q10), +19, +der(22)t(9;22)(q34;q11) and minor route ACA like -X, del(1)(q21), del(5)(q11q14), +10,-21, resulting in an unbalanced karyotype have been described to adversely affect outcome. Patients with minor route ACA (for example reciprocal translocations other than the t(9;22)(q34;q11) (e.g. t(1;21), t(2;16), t(3;12), t(4;6), t(5;8), t(15;20)) resulting in a balanced karyotype did not show differences in overall survival and progression free survival compared to patients with the standard translocation, a variant translocation or the loss of the Y chromosome. Aim of this study was to analyze the impact of the phenotype (myeloid or lymphoid) on time to BC and on cytogenetic pattern.

73 out of 1524 evaluable patients (4.8%) randomized until March 2012 to the German CML-Study IV (a 5-arm trial to optimize imatinib therapy) progressed to BC. Cytogenetic data of 23 out of 32 patients with myeloid BC and 14 out of 21 patients with lymphoid BC were available. In 15 patients, cytogenetic analysis were missing whereas 2 and 3 patients had megakaryoblastic and mixed phenotype, respectively and were not considered in this analysis. Karyotypes of lymphoid and myeloid BC were divided in major route and minor route ACA and balanced and unbalanced karyotypes. Categorical covariates were compared with Fisher’s exact test, while continuous covariates were compared with the Mann-Whitney-Wilcoxon test. Survival probabilities after BC were compared using the log-rank test.

Out of 23 patients with myeloid BC, 14 (61%) had major route unbalanced ACA (n=10) or minor route unbalanced ACA (n=4), 4 had minor route balanced ACA and 5 patients had the translocation t(9;22)(q34;q11) or a variant translocation t(v;22) without ACA.13 out of 14 (93%) patients with lymphoid BC had major route unbalanced (n=10) or minor route unbalanced ACA (n=3) and 1 had the standard translocation t(9;22)(q34;q11) only. Between myeloid and lymphoid BC, the difference in the distribution of unbalanced ACA was apparent, but not statistically significant (p=0.06). The most frequently observed major route ACA was trisomy 8 in both groups (7 vs. 6), +der (22)t(9;22)(q34;q11) was more frequently found in myeloid than lymphoid BC (6 vs. 2), +19 was found in both phenotypes (3 vs. 3) whereas an isochromosome i(17)(q10) and an isoderivative chromosome ider(22)t(9;22)(q34;q11) were less frequent and found only in myeloid BC (1 for each vs 0 for each aberration). In lymphoid BC, 5 of 14 patients (36%) had ACA which involved chromosome 7 (del(7)(q22) and -7) whereas in myeloid BC only 2 patients (9%) had -7 (p=0.08). The balanced karyotype with a translocation t(3;21)(q26;q22) and the translocation t(9;11)(p22;q23) described in acute myeloid leukemia was observed in 3 patients with myeloid CML (2 and 1, respectively) and in none with lymphoid phenotype. No differences were observed in time to BC for patients with lymphoid vs. myeloid BC (p=0.31, median time: 409 vs. 453 days) and survival after onset of BC (p=0.9, median time: 544 vs. 284 days).

The proportion of unbalanced karyotypes was higher in lymphoid than in myeloid BC. In lymphoid BC alterations of chromosome 7 were more often present whereas +der(22)t(9;22)(q34;q11) was observed more frequently in myeloid BC. The reciprocal translocations t(3;21)(q26;q22) and t(9;11)(p22;q23) described in acute myeloid leukemias were only observed in myeloid BC. However these cytogenetic differences do not seem to alter the course of BC.

Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Hehlmann:Novartis: Research Funding; BMS: Consultancy, Research Funding. Hochhaus:Ariad: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; BMS: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding, Travel Other. Müller:Novartis: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria, Research Funding; Ariad: Honoraria. Saussele:Pfizer: Honoraria; BMS: Honoraria, Research Funding, Travel, Travel Other; Novartis: Honoraria, Research Funding, Travel Other.