[Study of deletion of derivative chromosome 9 in patients with Ph+ chronic myeloid leukemia]

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

Cytogenetic analysis of bone marrow cells was performed by direct method and/or 24 h culture method. RHG banding was used for karyotype analysis. Dual-color and dual-fusion DNA probe was used to perform FISH for investigating the deletion of der(9) in Ph+ CML patients.

Cytogenetics studies showed typical Ph translocation in 76/105 and variant Ph translocation in 29/105 cases. Interphase-FISH studies showed deletion of der(9) in 12 (15.8%) of 76 patients with classic Ph translocation and in 4 (13.7%) of 29 patients with variant translocation. The frequency of deletion was similar in classic and variant translocations (P > 0.05). When the deletion was seen in the patient, it was present in all the Ph+ metaphases and nuclei. In 3 patients there were mixed cell populations with either 5'-abl or 3'-bcr deletion and all the 3 patients had both 5'-abl and 3'-bcr deletion. The median survival time of patients with deletion was significantly shorter than those without deletion (34 months vs 76 months; P < 0.05).

Deletion of der(9) is seen in about 1/6 of Ph+ CML patients in our study on Chinese CML patients, Ph+ CML patients with the deletion have shorter median survival time than those without it, indicating that it is a poor prognostic index.