Detection of 13q14 Deletion by FISH Is Not Sufficient to Define a Group of Good Prognosis Patients with Chronic Lymphocytic Leukemia.

In a cohort of 329 previously untreated newly diagnosed stage A CLL, we detected del13q by FISH in 172 patients (52%) using the D13S319 probe. Conventional cytogenetics was performed in the 105 cases with del13q followed in our institution. The other important prognostic markers ( ZAP70, IgVH, CD38, proliferation markers) and clinical progression were also available for all patients.

We first studied the large cohort of stage A patients and found that deletion 13q had no prognostic impact on PFS. When considering more specifically the presence of deletion 13q as sole anomaly (n=143), PFS was not significantly different from that of patients with no aberration detected by FISH analysis (del 13q, del11q, del17p and trisomy 12) (n=98). Moreover, the distribution of prognostic factors (ZAP70, sTK, mutational status, CD38 expression, lymphocytosis) was not statistically different among these two groups.

We aimed at deciphering further these del13q cases through analysis of the percentage of deleted cells, the presence of mono versus biallelic deletions, and the presence of additional aberrations as detected by FISH and conventional cytogenetics in the 105 del13q cases followed in our institution.

The size of the del13q clone, as reflected by the percentage of del13q cells by FISH, was highly variable, ranged from 7 to 90 %, and had no prognostic significance on PFS.

Monoallelic deletions were present in 77 cases, fully biallelic deletions in 9 cases, and concomitant bi and monoallelic deletions in 19 cases. The 9 cases with biallelic deletions had a significantly shorter PFS and were associated with other unfavorable prognostic markers. As biallelic deletions are most likely to represent progression from monoallelic cases, it is understandable that no clear prognostic impact was evidenced between cases with monoallelic deletions and with concomitant variable amount of bi and monoallelic deleted cells. Twenty cases (20 monoallelic and 6 biallelic) were further studied by array-CGH. Minimal deleted region (MDR) was included in all deletions but the size of the deletion was variable and in most cases much larger than MDR. Among the 6 bi allelic cases, one of the deletions was restricted to the MDR in all cases, pointing out to the importance of the level of miRNA expression.

Additional aberrations were found in 44/105 del13q cases. In 17 patients, one or more alterations were detected by FISH techniques : del11q (n=8), trisomy 12 (n=8) or del17p (n=5). By conventional cytogenetic all these aberrations were also detected, as well as other rare ones in 16 additional cases, either isolated or associated in a complex karyotype in 5 cases. Presence of additional aberrations had a significant unfavourable impact on PFS, even when excluding del11q, del17p and tri12, and considering the non recurrent aberrations that were detected by conventional cytogenetics only.

Presence of 13q deletion should not be considered as a good prognostic marker by itself among stage A patients. Moreover, del13q cases are highly heterogeneous, and the presence of deletion 13q should not be interpreted without considering both alleles or the presence of concomitant genetic alterations.

No relevant conflicts of interest to declare.