TP53 Alterations In CLL - Parameters Influencing The Prognostic Impact: A Study On 3,988 Patients
Authors: Haferlach Claudia , Dicker Frank , Jeromin Sabine , Weissmann Sandra , Roller Andreas , Worseg Wenke , Alpermann Tamara , Kern Wolfgang , Haferlach Torsten , Kohlmann Alexander , Schnittger Susanne 
Published: October 2019

Abstract

Background
In CLL, the TP53 gene may be inactivated by deletion and/or mutations. Most cases with 17p deletion also carry TP53 mutations on the second allele. However, in a subset of cases only one allele seems to be disrupted by either mutation or deletion. It is still a matter of debate whether monoallelic TP53 abnormalities have the same poor prognostic effect as biallelic alterations. Further, a small subset of patients with TP53 deletions harboring mutated IGHV genes were described to exhibit a slowly progressive disease without treatment indication for years.

Aims
In this study, we addressed the following questions: 1. Frequency of TP53 alterations: mutation and deletion. 2. Characterization of the TP53 altered subsets with respect to IGHV mutation status, other molecular mutations and cytogenetics. 3. Impact on survival.

Patients and Methods
3,988 CLL patients were analyzed by DNA sequencing for TP53 mutations and by FISH for TP53 deletion status as well as for del(13q), del(11q) and +12. IGHV mutation status was determined in 3,505 patients. Further, SF3B1 (n=1,245), MYD88 (n=1,026), XPO1 (n=1,025), NOTCH1 (n=973), and FBXW7 (n=962) were analyzed by DNA sequencing.

Results
488/3,988 (12.2%) harbored a TP53 mutation (TP53mut) and 308/3,988 (7.7%) patients showed a TP53 deletion (TP53del) by FISH. 268 cases (6.7%) showed both a TP53del and a TP53mut, while 220 cases (5.5%) harbored a TP53mut only and 40 (1.0%) a TP53del only. 20.5% of TP53mut cases harbored more than one TP53mut. The frequency of TP53mut and TP53del increased significantly with age (≤40 yrs: 2.4%/2.4%; 41-50 yrs: 7.5%/4.0%; 51-60 yrs: 12.4%/6.8%; 61-70 yrs: 12.1%/8.1%; 71-80 yrs: 13.4%/9.1%; >80 yrs: 16.0%/9.9%; p=0.006 and p=0.013, respectively). In the entire cohort, 1,428/3,505 (40.7%) cases showed an unmutated and 2,077/3,505 (59.3%) a mutated IGHV status. The lowest frequency of IGHV unmutated was observed in cases without TP53 alteration (1,148/3,094; 37.1%) and the highest in patients with both TP53mut and TP53del (156/201; 77.6%). The frequency was in between in patients with TP53mut sole (106/176; 60.2%) and TP53del sole (18/34; 52.9%). Patients with both TP53mut and TP53del as well as patients with TP53del sole had a significantly shorter overall survival (OS) compared to patients with TP53mut sole or patients without TP53 alteration (OS at 5 yrs: 40.2% vs. 36.4% vs. 68.8% vs 85.4%; p<0.001; TP53mut sole vs TP53wt: p=0.003). Next, we evaluated the impact of the TP53 mutation load on survival. Therefore, we divided patients into 10 subgroups according to their mutation load (increments of 10%). The OS of patients with a mutation load <20% (n=150) did not differ from patients with TP53wt, while a mutation load ≥20% was significantly associated with shorter OS (HR: 4.9, p<0.001). An unmutated IGHV status was associated with shorter OS in the total cohort (HR: 2.3, p<0.001). In the subset of patients with TP53wt an unmutated IGHV status was also an adverse prognostic factor (OS at 5 yrs: IGHV unmutated vs mutated: 80.3% vs 88.6%, p=0.007). This was true also in cases with TP53del sole (median OS: 12 months vs not reached, p=0.001). In contrast, in patients with either TP53mut sole or both TP53mut and TP53del the IGHV status had no impact on OS. In the entire cohort univariate Cox regression analysis revealed the following parameters to be significantly associated with OS: TP53mut (HR: 4.0), TP53mut ≥20% (HR: 4.9), TP53del (HR: 7.1), IGHV unmutated (HR: 2.3), age >60 yrs (HR: 3.3), del(11q) (HR: 2.1), del(13q) sole (HR: 0.6), SF3B1mut (HR: 2.5) (for all p<0.001), and NOTCH1mut (HR: 1.6, p=0.025). Multivariate Cox regression analysis including parameters significantly associated with OS in univariate analyses revealed the following factors to be independently associated with shorter OS: TP53del (HR: 4.2, p<0.001), TP53mut ≥20% (HR: 2.4, p=0.008), age >60 yrs (HR: 2.6, p<0.001), SF3B1mut (HR: 2.4, p<0.001), and del(11q) (HR: 2.2, p=0.002).

Conclusions
1. TP53 alterations were observed in 13.2% of CLL patients, 6.7% showed both a deletion and a mutation, while 1% showed a deletion only and 5.5% a mutation only. 2. Both TP53 mutations and TP53 deletions are associated with an unmutated IGHV status. 3. TP53 deletions had the most adverse impact on survival, TP53 mutations had a significant impact on OS only if the mutation load was ≥20%. A small subset of patients with TP53 deletion sole and a mutated IGHV status seems to have a favorable outcome.

Disclosures:
Haferlach: MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Dicker:MLL Munich Leukemia Laboratory: Employment. Jeromin:MLL Munich Leukemia Laboratory: Employment. Weissmann:MLL Munich Leukemia Laboratory: Employment. Roller:MLL Munich Leukemia Laboratory: Employment. Worseg:MLL Munich Leukemia Laboratory: Employment. Alpermann:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Kohlmann:MLL Munich Leukemia Laboratory: Employment. Schnittger:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.