Time to first treatment and P53 dysfunction in chronic lymphocytic leukaemia: results of the O-CLL1 study in early stage patients

Abstract

Chronic lymphocytic leukaemia (CLL) is characterised by a heterogeneous clinical course. Such heterogeneity is associated with a number of markers, including TP53 gene inactivation. While TP53 gene alterations determine resistance to chemotherapy, it is not clear whether they can influence early disease progression. To clarify this issue, TP53 mutations and deletions of the corresponding locus [del(17p)] were evaluated in 469 cases from the O-CLL1 observational study that recruited a cohort of clinically and molecularly characterised Binet stage A patients. Twenty-four cases harboured somatic TP53 mutations [accompanied by del(17p) in 9 cases], 2 patients had del(17p) only, and 5 patients had TP53 germ-line variants. While del(17p) with or without TP53 mutations was capable of significantly predicting the time to first treatment, a reliable measure of disease progression, TP53 mutations were not. This was true for cases with high or low variant allele frequency. The lack of predictive ability was independent of the functional features of the mutant P53 protein in terms of transactivation and dominant negative potential. TP53 mutations alone were more frequent in patients with mutated IGHV genes, whereas del(17p) was associated with the presence of adverse prognostic factors, including CD38 positivity, unmutated-IGHV gene status, and NOTCH1 mutations.

Figure 1

Analysis of the prognostic impact of TP53 alterations in the O-CLL1 cohort. Kaplan–Meier curves of cases differently clustered on the basis of the presence of a TP53 mutation and del(17p). O-CLL1 patients were divided in different groups: WT/noDel patients with neither a TP53 mutation nor del(17p); Mut/noDel and Mut (germline)/noDel, patients with a TP53 mutation (somatic or germline, respectively) and without del(17p); Mut/Del, patients that show both a TP53 mutation and del(17p); WT/Del, patients harbouring only del(17p).

Figure 2

Influence of residual functionality of mutated P53 proteins on TTFT in O-CLL1 patients. Kaplan–Meier curves of cases belonging to the MUT/noDel group, clustered on the basis of (A) residual transactivation ability of the mutated P53 protein (≥ 20% versus < 20% with respect to WT P53) as determined in the yeast reporter strain yLFM-P21-5′; (B) dominant-negative (DN) or recessive (rec) classification of the mutated P53 protein, as determined in the yeast reporter strain yLFM-P21-5′.

Figure 3

Analysis of the prognostic impact of TP53 alterations in O-CLL1 cohort study. Cox multivariate analysis of biological and clinical variables found to be significant on univariate analysis. Presence of a TP53 mutation associated with del(17p) was forced in the model as measure of P53 dysfunction.

Figure 4

Determination of variant allele frequency (VAF) at 36 months after diagnosis or at progression in O-CLL1 cohort study. TP53 mutational status was re-assessed in 171 patients by NGS after 36 months from the initial test or at disease progression. Presented are the 8 cases with a TP53 mutation at diagnosis, which continued to express the same mutation, albeit with some degree of clonal expansion. FISH analysis for del(17p) was repeated in all cases after 36 months (36 m, red bars) or at the time of therapy need (prog, red bars): none of the cases negative for del(17p) (Mut/noDel) became del(17p) positive. Percentage increase in the VAF of the samples analysed at 36 m/prog, compared to the samples at T0 (grey bars), are indicated in the figure only for cases in which it clearly occurred (CA0082, DD0478, GM0252, PA0254, PG0028). The increment was calculated according to the formula: (VAF 36 m/prog–VAF T0)/VAF 36 m/prog × 100. Of the two cases that experienced progression, PG0028 presented an increase of the percentage of del(17p) positive cells and of VAF (78%). The other case (AA0396) showed no increase in VAF.