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Letters to the Editor
genes, including patients with PD (Online Supplementary Table S1).
Among the 14 R/R patients, prior to ibrutinib treat- ment four patients (29%) resulted TP53 WT and ten (71%) mutated by deep-sequencing analysis. Four of 11 (37%) carried the del(17p) and seven (50%) showed unmutated IGHV. Thirty-one TP53 mutations (3.1 muta- tion/patient; range, 1-11) were identified: 11 (35.5%) were major (mean VAF 31.9%; range, 10.5-78.8) and 20 (64.5%) minor (mean VAF 2.9%; range 1-6.8). Five patients carried one or two major mutations (#8271, #5708, #3547, #9225, #7458), three cases showed a com- plex mutational architecture (#5717, #8353 and #3425); two patients showed only minor mutations (3 in #3546 and 11 in #8540, respectively); four patients had no mutations (Online Supplementary Table S2). As expected, before ibrutinib, the TP53 mutational load of R/R patients was higher and more complex than that of TN patients. In the R/R patients, eight of 31 (26%) TP53 mutations (4 major and 4 minor) decreased, eight of 31 (26%) (4 major and 4 minor) persisted stable, 11 of 31 (35%) (2 major and 9 minor) were undetectable, four of 31 (13%) (2 major in #7458 and #8353; 2 minor in #3546) increased in three patients, and two novel minor muta- tions emerged in two cases already TP53-mutated prior to ibrutinib treatment (cases #5717, #3425) (Table 1; Online Supplementary Table S2). No novel TP53 mutations arose in TP53 WT patients over time under ibrutinib. In R/R patients, because of the more complex mutational profile of each patient we could not identify patient-relat- ed patterns, rather we documented different dynamics of different TP53 mutations within the same patient (Online Supplementary Table S2), possibly due to a different sensi- tivity to the drug, as suggested.12,13 Among R/R patients, four TP53-mutated and two WT continued ibrutinib (#8540, #6856, #3547, #9225, #5717, #6123), four dis- continued ibrutinib for adverse events (#5708, #8353, #7458, #3380), one shifted to venetoclax (#3425), three died (#3546, #8991, #8271).
No significant changes were observed in the mean CCF of TP53 mutations before and after ibrutinib: 60.7% versus 43.1% and 20.5% versus 20.2%, in TN and R/R patients, respectively. On the contrary, the lymphocyte count decreased significantly after ibrutinib treatment in TP53-mutated patients from both cohorts: from 40.7x109/L (range: 4.9-132.2x109/L) to 11.2x109/L (range, 1.2-135.7x109/L) (P=0.018, Mann-Whitney test) and from 39.7x109/L (range, 1.5-99.0x109/L) to 7.1x109/L (range, 1.4-18.9x109/L) (P=0.034), respectively. The decrease in lymphocytosis in the presence of a stable TP53 mutations CCF proves the effectiveness of ibrutinib both on TP53-mutated and WT CLL cells, regardless of previous therapies, at least during the first years of treat- ment.
In 13 of the 14 R/R patients, TP53 mutations were ret- rospectively evaluated by deep sequencing also before each line of CIT. At the first evaluated time point, three patients were mutated (2 with minor and 1 with one major mutation) and ten resulted WT; of the latter, six acquired major or minor TP53 mutations over time. Overall, among the nine mutated cases, 29 mutations were identified with the following dynamics: 13 (45%) (3 major and 10 minor) novel mutations emerged, seven (24%) minor mutations increased, six (21%) (3 major and 3 minor) persisted stable and three (10%) (1 major and 2 minor) decreased. The decrease in CCF for the latter was from 84.44% to 46%, from 3.3% to 2.01% and from 4.69% to 1.83%, respectively. No mutation was unde- tectable. While the increased and novel mutations were
significantly more common during the CIT phase (20/29 vs. 6/33, during CIT and ibrutinib, respectively; P<0.0001, Fisher’s exact test), the decreased and unde- tectable mutations were more frequent under ibrutinib treatment (3/29 vs. 19/33, during CIT and ibrutinib, respectively; P<0.0001) (Table 1).
In the present study, in TP53-mutated TN and R/R CLL patients, ibrutinib appears to decrease the major and minor mutations’ numerosity and complexity, since most mutations decreased (39% and 24%) or were unde- tectable (17% and 34%) and one third of mutations remained stable. On the other hand, a small proportion of TP53 mutations (9%, 2 minor, in TN; 13%, 2 major and 2 minor, in R/R cases) increased in CCF under ibruti- nib treatment, although without clear clinical conse- quences with the current follow-up. We observed no association between the dynamics of TP53 mutations and the type of mutation, or the exon involved, neither the type of karyotype (data not shown) nor the presence of del(17p) (8 TN with vs. 9 without del(17p), decreased/undetectable vs. increased/novel mutations, P=0.46; 4 R/R with vs. 3 without del(17p), P=1 at Fisher’s exact test).
With a prolonged follow-up of more than 2 years, up to 44 months, our data add to the initial findings of a gener- al stability of TP53 subclones over the early treatment period and support the notion that there is no specific positive selection of TP53 mutations under ibrutinib.7,14 Emergence of novel mutations proved exceptional events, mainly limited to R/R patients that display from the beginning a more complex mutational architecture, suggesting a potential influence of the previous CIT.13
However, in the long-term TP53 disrupted CLL patients tend to experience an inferior outcome.12,13 This can be due to an intrinsic genomic instability and a greater possibility of acquiring additional mutations con- ferring drug resistance and more frequent relapses in the long-term.7 Moreover, in vitro apoptosis and inhibition of proliferation are inferior in TP53 mutated than in WT cells exposed to ibrutinib, pointing to different mecha- nisms of cell fitness control in addition to the BCR path- way,15 that can make the difference over time.
In conclusion, in TP53-mutated CLL patients ibrutinib in any line of therapy decreases the TP53 complexity at least within the first years of treatment and it does not exert a positive selective pressure on pre-existing TP53 mutated clones, unlike CIT. In TP53 WT patients, ibruti- nib never induced the emergence of novel TP53 muta- tions after >2 years of exposure. These findings reinforce a broader use of a BTK inhibitor rather than CIT in the management of CLL, particularly for patients with an unfavorable genetic profile or with R/R disease.
Luciana Cafforio,1 Sara Raponi,1 Luca Vincenzo Cappelli,1 Caterina Ilari,1 Roberta Soscia,1 Maria Stefania De Propris,1 Paola Mariglia,1 Gian Matteo Rigolin,2 Antonella Bardi,2 Nadia Peragine,1 Alfonso Piciocchi,3 Valentina Arena,3 Francesca Romana Mauro,1 Antonio Cuneo,2 Anna Guarini,4 Robin Foà1 and Ilaria Del Giudice1
1Hematology Section, Department of Translational and Precision Medicine, Sapienza University, Rome; 2Hematology Section, Department of Medical Science, Azienda Ospedaliero-Universitaria Arcispedale S. Anna, University of Ferrara, Ferrara; 3GIMEMA Data Center, GIMEMA Foundation, Rome and 4Department of Molecular Medicine, Sapienza University, Rome, Italy
Correspondence:
ILARIA DEL GIUDICE - delgiudice@bce.uniroma1.it
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haematologica | 2022; 107(1)