The Prognostic Value of TP53 Mutations in Chronic Lymphocytic Leukemia (CLL) Is Independent of del17p13: Implications for Overall Survival and Chemorefractoriness

CLL harboring del17p13 displays a dismal prognosis and a high risk of chemorefractoriness. We tested whether TP53 inactivation through mutation harbors the same prognostic role as del17p13 on 308 consecutive CLL. TP53 mutation status was assessed at diagnosis by direct sequencing of TP53 exons 2–10. Thirty-two TP53 mutations were observed in 31/308 (10.0%) CLL. Among 26 missense mutations, the median residual transactivation activity compared to germline TP53 was 8.9% (25^th–75^th percentile: 0.6–13.0%), and was ≤20% in 22/26 (84.6%) mutations. All microdeletions and microinsertions (4/32; 12.5%) led to frameshift. One non-sense mutation introduced a stop codon at position 213, and one mutation affected the 3′ splicing site of exon 8. Despite the statistical association between TP53 mutations and del17p13 in the whole cohort, the overlap between the two genetic lesions was restricted to a fraction of patients. By combining results of FISH and TP53 mutation analysis, 44/297 (14.8%) CLL carried TP53 inactivation: 18/44 (40.9%) showed TP53 mutation paired to del17p13; 10/44 (22.7%) showed TP53 mutations in the absence of del17p13; and 16/44 (36.3%) showed del17p13 in the absence of TP53 mutations. Univariate log-rank analysis identified both TP53 mutations and del17p13 as risk factors for short overall survival (OS). Median OS for patients with TP53 mutations was 79.6 months (5-year OS 66.2%), whereas median OS for patients without TP53 mutations was not reached and the 5-year OS was 85.2% (p<.001). Multivariate analysis selected TP53 mutations (HR 3.20; p=.002), along with age >65 years (HR 4.98; p<.001) and advanced Binet stage (HR 3.01; p<.001), as independent predictors of OS after adjustment for del17p13 and other potentially confounding biological and clinical covariates. Univariate log-rank analysis identified both TP53 mutations and del17p13 as risk factors of short time to chemorefractoriness. Median time to chemorefractoriness for patients with TP53 mutations was 6.3 months versus 72.7 months for patients without TP53 mutations (p<.001). Multivariate analysis selected TP53 mutations (HR 3.97; p<.001) as independent predictor of short time to chemorefractoriness after adjustment for del17p13 and other potentially confounding covariates. OS and time to chemorefractoriness did not differ between CLL harboring TP53 mutations in the absence of del17p13 and CLL harboring del17p13. Patients harboring TP53 mutations only and patients harboring both TP53 mutation and del17p13 were characterized by short time to chemorefractoriness compared to patients without any TP53 alteration or to patients harboring del17p13 only (p<.05). CLL that at diagnosis harbored del17p13 without TP53 mutations showed a significantly longer time to chemorefractoriness compared to CLL who at diagnosis carried both del17p13 and TP53 mutations (median: 55.2 months vs 5.5 months, respectively; p=.003). Notably, at diagnosis, the percentage of deleted nuclei was significantly lower in CLL harboring del17p13 only (median: 45.0%, 25^th–75^th percentiles: 7.3–67.4%) compared to CLL with both del17p13 and TP53 mutations (median: 66.5%, 25^th–75^th percentiles: 52.1–77.9%, respectively) (p=.020). The value of TP53 mutations in predicting chemorefractoriness was also assessed in patients who had been exposed to fludarabine (n=88). Multivariate analysis selected TP53 mutations as the sole independent predictor of short time to fludarabine refractoriness (HR 6.72; p<.001). Sequential samples were available for 14 CLL who had no TP53 abnormalities at diagnosis and who later developed chemorefractoriness. At the time of chemorefractoriness, TP53 abnormalities were acquired in 5/14 (35.7%) cases. The implications of this study are threefold:

• mutation in the absence of del17p13 is the sole mechanism of TP53 inactivation in 20% CLL harboring TP53 disruption;

• TP53 mutations carry the same prognostic relevance as del17p13 in terms of CLL progression, survival and risk of chemorefractoriness;

• because of the practical implications for choice of therapy, screening for TP53 mutations, in addition to del17p13 assessment, should be included in the initial prognostic assessment of CLL.