Clinical and Interphase-FISH Studies of Deletion of Derivative Chromosome 9 in Patients with Chronic Myelogenous Leukemia.

Objective: To determine the frequency of the deletion of derivative 9 [der(9)] among chronic myeloid leukemia (CML) patients with classic Ph translocation and variant Ph translocation, and to assess the association between this deletion and clinical prognosis.

Methods: Cytogenetical analysis of bone marrow cells was performed by direct method and /or 24h culture method. RHG banding was used for karyotype analysis. Dual-color and dual-fusion DNA probe was used to perform interphase-FISH to investigate the deletion of der(9) in Ph+ CML patients and all patients were followed up.

Result: Cytogenetical studies showed typical Ph translocation in 76/105 and variant Ph translocation in 29/105. Interphase-FISH studies showed deletion of der(9) in 12 cases(15.8%) of 76 patients with classic Ph translocation and in 4 cases (13.7%) of 29 patients with variant translocation. The frequency of deletion was similar in classic and variant translocations (P>0.9). This result is contrary to previous reports which suggested that deletions are much more common in variant Ph translocation than in classic Ph translocation. When the deletion was seen in a patient, it was present in all the Ph+ metaphases and nuclei. Three patients with heterogeneous cell populations mixed with cells with single 5′-ABL or 3′-BCR deletion and with both 5′-ABL and 3′-BCR deletion. It may suggest clone evolution in the progression of deletion. Complete clinical information was available in 54 patients. There were no significant difference in peripheral leukocyte count, platelet count, hemoglobin and percentage of peripheral blood blast cells between patients with and without der(9)deletion. However, the results of following up showed that the median survival time of patients with der(9) deletion was significantly shorter than those without der(9) deletion (34 months vs 76 months; P<0.05, log-rank Test).

Conclusion: A deletion of der(9) is seen in about 1/6 Ph+ CML patients in china, with which Ph+ CML patients have shorter median survival time than those without it, indicating that it is a poor prognostic index. For evolution the prognosis of CML patients more precisely, it is best to perform cytogenetical analysis and FISH analysis for der(9) deletion simultaneously at diagnosis.