Retinoblastoma gene deletions in b‐cell chronic lymphocytic leukemia

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Abstract
Approximately 10% of B‐cell chronic lymphocytic leukemia (B‐CLL) cases have structural chromosomal aberrations involving band 13q14. To evaluate a possible role of RB1 gene deletions in B‐CLL we investigated the malignant cells of 27 patients by molecular genetic and cytogenetic techniques. Four of the cases had chromosomal aberrations that involved 13q14 (including one case with a 13q14 deletion that was observed in a single metaphase cell), and 11 had other chromosomal abnormalities, whereas the malignant cells of 12 patients were either cytogenetically normal or failed to divide in vitro. Eight patients (30%) were found to have hemizygous deletions of the RB1 gene. These cases included all four patients with chromosomal changes at 13q14, but also three patients without chromosome abnormalities and one case with a chromosomal aberration not involving 13q. The deletions were interstitial in all cases but one, as defined by probes located centromeric and telomeric of the RB1 locus. Inactivation of RB1 may thus be a significant event in the development of some B‐CLL clones.