Mutational and Cytogenetic Analyses Of 177 CLL Patients With Trisomy 12: A Retrospective Study Of The CLL French Intergroup

Cytogenetic abnormalities are of key importance for predicting clinical course and response to therapy in patients with chronic lymphocytic leukemia (CLL). Trisomy 12 (tri12), the third most frequent chromosomal aberration in CLL patients (10-20%), is associated with an intermediate prognostic risk but represents a clinical heterogeneous entity. Recently, next generation sequencing have revealed recurrent mutations in genes that were unknown to be involved in CLL pathogenesis, including NOTCH1, MYD88, SF3B1, XPO1 and BIRC3. In patients harboring tri12, NOTCH1 mutations have been shown to be present in up to 25% of cases and to confer unfavorable outcome explaining in part the clinical heterogeneity of tri12 patients. To better understand the genetic basis and prognosis of tri12 patients, we performed a multicenter retrospective study combining extensive mutational and cytogenetic analysis.

Patients carrying tri12 were identified using fluorescence in situ hybridization (FISH) and/or chromosome banding (CB). Main clinical and biological characteristics were collected and included in univariate analysis of prognostic factors, comprising age, Binet stage (A vs. B-C), splenomegaly, lymphocyte doubling time (LDT), LDH, beta2microglobulin (B2M), CD38 expression, IGHV mutational status, percentage of interphase nuclei positive (INP) for tri12, additional FISH (del13q, del11q, del17p) or chromosomal aberrations and presence of complex karyotype (> 2 CB abnormalities). Search for mutations was performed by Sanger direct sequencing for TP53 (exons 5-10), NOTCH1 (exon 34), MYD88 (exons 14-16), SF3B1 (exons 14-16) and XPO1 (exons 14-15). Primary and secondary endpoints were time to first treatment (TFT), response to therapy, time to next treatment (TNT) and overall survival (OS).

The study population comprised a total of 177 untreated patients including 112 and 75 patients with stage A and B-C CLL, respectively. The median age at diagnosis was 62 years old (range, 31-87) and 33% of patients were female. B2M was superior to 4 mg/L in 30/92 (32%) patients and LDH elevated in 65%. CD38 expression was positive (>30%) in 58% and IGHV status was unmutated in 60%. Among the whole study population, all patients were positive for tri12 by FISH and 158/165 by CB. Tri12 was associated by CB with tri19 in 21 patients (13.2%), tri18 in 12 patients (7.5%), tri3 in 1 patient (<1%), t(14;18) in 9 patients (5.7%), t(14;19) in 3 patients (2%) and del14q in 7 patients (4.5%). Complex karyotype was present in 42 patients (26%) and tri12 was the sole abnormality observed by CB in 71 patients (45%). Out of 170 patients analysed with the four probes by FISH, tri12 was the sole abnormality in 114 patients (67%) and was associated with del13q, del11q and del17p in, respectively, 44 (26%), 8 (4%) and 10 (6%) patients. The median percentage of INP for tri12 was 58% (range, 5-100). TP53, NOTCH1, MYD88 and SF3B1 mutations were tested in 113 patients and identified in, respectively, 9 (8%), 19 (17%), 1 (<1%) and 1 (<1%) patients. No mutation of XPO1 was observed. Among the stage A population of 112 patients, 64 (57%) needed treatment with a median TFT of 45 months (range, 1-170). A shorter TFT was significantly associated with a LDT inferior to one year (P=0.0001), and the presence of TP53 (P=0.04) mutation while the presence of another trisomy (P=0.03) was associated with a significantly longer TFT. By multivariate analysis, only TP53 mutation retain prognostic significance for TFT (HR=3.9, 95%CI=1.02-15.04). Among the 75 stage B-C patients, 62 were treated, 51 evaluable for response to therapy and 28 received a second line of treatment. The only prognostic variable associated with poor response to therapy was the presence of NOTCH1 mutation (P=0.01). Finally, regarding the whole tri12 population, Binet stage (A vs. B-C), splenomegaly, lymphocytosis, LDH, B2M, the percentage of INP and the IGHV unmutated status were associated with worst OS in univariate analysis.

The most frequent molecular abnormalities observed in our tri12 cohort were TP53 and NOTCH1 mutations that occurred in, respectively, 8 and 17% of cases. NOTCH1 mutations were associated with poor response to therapy and TP53 mutations with a shorter time to first treatment.

Leblond:Mundipharma: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau; Janssen: Honoraria, Membership on an entity’s Board of Directors or advisory committees; Roche : Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau.