Structure and prognostic signifi cance of 13q14 deletion in chronic lymphocytic leukemia

Abstract

Introduction. 13q14 deletion is the most common chromosomal abnormality in chronic lymphocytic leukemia (CLL), and as the sole abnormality determines the most favorable prognosis of the disease. Using molecular genetic methods two subtypes of 13q14 deletion were identifi ed based on the size of the lost chromosomal material: small (type I) with the involvement of the D13S319 segment containing MIR15A/MIR16-1 and DLEU1 genes and large (type II) containing centromeric region of 13q14 involving RB1 gene. Data on the impact of type I and II deletions on the course of CLL are controversial.Aim — to evaluate the prognostic signifi cance of different variants of 13q14 deletion in CLL.Patients and methods. The study enrolled two cohorts of CLL patients. Cohort 1: 256 patients who were studied by FISH with DNA probes for detection of 13q14/D13S319, 11q23/ATM, 17p13/TP53 deletions, and trisomy 12 before immunochemotherapy. 101 patients with identifi ed 13q14/D13S319 deletion were analyzed with a DNA probe for RB1 locus for determination of deletion size (type I or type II). Cohort 2: 28 patients at different stages of the disease with deletion 13q14 detected by FISH were studied by using combination of standard and molecular cytogenetic methods (mFISH, mBAND, arrayCGH) to clarify the structure of 13q abnormalities.Results. In Cohort 1 chromosomal aberrations were detected in 75 % of patients: 13q deletion — 52 % (isolated — 36 % of all cases and 48 % of cases with deletion), 11q deletion — 19 %, +12 — 13 %, 17p deletion — 6 %. 13q14 deletion type I was detected in 56 %, type II — in 44 % of patients. Type II deletion correlated with the presence of 11q deletion (p = 0.05). Isolated deletions of type I and II were found in 61 and 39 %, respectively. Biallelic deletion was identifi ed in 12.7 % of patients with 13q deletion. Statistically signifi cant differences in OS were obtained in type I and II groups of patients with isolated 13q14 deletions: median OS was not reached and made 67.5 months, respectively, p = 0.05. In Cohort 2 structural abnormalities of chromosome 13 by conventional cytogenetic analysis (CCA) were identifi ed in 50 % of cases: 13q deletion — 11 cases; translocations involving 13q14 — 6 cases. In 5 cases with biallelic deletion identifi ed by FISH, 13q14 deletion by CCA was detected in two patients, and only in one allele.Conclusion. In general, 13q14 deletion is a cytogenetic factor of favorable prognosis for CLL but its structure is heterogeneous. Loss of tumor suppressor RB1 (type II deletion) negatively affects OS in patients treated with immunochemotherapy