Despite CLL is a disease of the elderly with a median age at onset around 70 years, the majority of published clinical trials until 2010 enrolled patients with a median age between 58 and 64 years [
42]. The need of clinical trials specifically designed for older patients was recognized and the CLL5 trial showed that purine analog fludarabine was not superior to chlorambucil in older patients [
43]. While bendamustine with the anti CD20 monoclonal antibody rituximab (BR) was shown to be an effective treatment in fit patients >65 years [
11] and guidelines for the usage of bendamustine in CLL were published [
12], the CLL 11 trial was specifically designed for elderly and unfit patients. In this randomized phase 3 study, single agent chlorambucil was compared with chlorambucil associated with the anti CD20 monoclonal antibody rituximab or the second generation anti CD20 obinutuzumab [
10]. Chlorambucil plus obitutuzumab (Chlor+O) produced a significant PFS advantage as compared with the chlorambucil and rituximab. Furthermore, 37.7% of the patients who received chlorambucil and obinutuzumab attained an undetectable minimal residual disease in the peripheral blood and experienced prolonged PFS, especially in those cases with a favorable genetic profile, i.e., with a mutated configuration of the immunoglobulin gene [
10]. Thus, the combination of Chlor+O or the BR regimen became standard treatment regimens for older patients [
44].
4.1. Bruton Tyrosine Kinase Inhibitors
Five randomized trials showed the superiority of the BTKi ibrutinib, acalabrutinib and zanubrutinib as compared with chemo(immuno)therapy in previously untreated older patients. The salient efficacy data at the time of the primary pre-planned analyses in these trials are summarized in Table 1 and the incidence of adverse events of clinical interest are reported in Table 2.
Table 1.
Results of phase-3 clinical trials comparing the BTKi Ibrutinib, acalabrutinib and zanubrutinib or venetoclax-containing regimens versus standard chemo(immuno)therapy in older patients.
Table 1.
Results of phase-3 clinical trials comparing the BTKi Ibrutinib, acalabrutinib and zanubrutinib or venetoclax-containing regimens versus standard chemo(immuno)therapy in older patients.
|
N. of Patients
|
Median Age |
Median Follow-Up (months) |
% TP53 Aberrations |
PFS |
OS |
Reference |
BTKi vs comparator |
IBR vs. CHLOR |
269 |
Median age 72–73 yr |
18.4 |
0% |
18-months PFS: IBR 90%; Chlor 52% |
2-yr OS: IBR 98%, Chlor 85% |
50 |
IBR vs. IBR+R vs BR. |
547 |
71 y |
38 |
10% |
2-yr PFS: IBR 87%; IBR+R 88%; BR 74% |
2-yr OS: IBR 90%, IBR+R 94%, BR 95% |
21 |
IBR+O vs CHLOR+O |
229 |
70-72 |
31.3 |
16%/20% |
30-month PFS: IBR+O 77%; CHLOR +O 16% |
30-month OS: IBR+O 86%; CHLOR+O 85% |
105 |
ACALA+O, ACALA, CHLOR+O |
535 |
Median age 70 yr |
28.3 |
9% |
2-yr PFS: ACALA 87%; ACALA+O 93%; CHLOR+O 47% |
2-yr OS: ACALA 95%; ACALA+O 95%; CHOLOR+O 92% |
24 |
ZANU, BR |
479 |
Median age 70 yr,
|
26.2 |
0% |
24-mo PFS: ZANU 85.5%; BR 69.5% |
24-mo OS: ZANU 94.3%, BR 94.6% |
15 |
Venetoclax containing regimen vs comparator |
V+O vs. CHLOR+O |
432 |
72–74 |
28.1
|
11.1%
|
24-mo PFS: VO (88.2%) CHLOR+O: 64.1%
|
24-mo OS: VO 91.8% CHLOR+O 93.3% |
20 |
IBR+V vs CHLOR+O |
211 |
71
|
27.7 |
4.3% |
30-mo PFS: IBRU+V 80.5% CHLOR+O 35.8% |
NR |
23 |
Table 2.
Grade ≥3 adverse events of clinical interest with BTKi in phase-3 clinical trials comparing standard chemo(immuno)therapy and BTKi in older patients.
Table 2.
Grade ≥3 adverse events of clinical interest with BTKi in phase-3 clinical trials comparing standard chemo(immuno)therapy and BTKi in older patients.
Trial |
Median Follow-Up (months) |
Afib(*) |
Hypertension |
Bleeding |
Arthralgia |
Reference |
Resonate-2 |
18.4 |
IBRU *6%/1.5% CHLOR 0.7% |
IBRU 4% CHLOR 0% |
IBRU 4% CHLOR 2% |
IBRU 16%** CHLOR 7% |
106 |
Alliance
|
38 |
IBR *17%/9%; IBR+R *14%/6% BR 3%/3% |
IBR 29%, IBR+R 34% BR 15% |
IBR 2% IBR+R 4% BR 0% |
NR |
21 |
iLLUMINATE |
31.3 |
IBRU+O *12%/5% CHLOR+O 0% |
IBRU+O 4% CHLOR+O 4% |
NR |
IBRU+O 1% CHLOR+O 0% |
105 |
ACAL+O, ACAL, CHLOR+O |
28.3 |
A *4% A+O *3% CHLOR+O: *1% |
A 2% A+O 3% |
A 2% A+O 2%
|
A 0.6%; A+O 1.1% |
24
|
SEQUOIA |
26.2 |
ZANU *3% BR *3% |
ZANU 6% BR 5% |
ZANU 3.5% BR 1.5% |
ZANU 1% BR 0.5% |
15
|
Updated results with longer follow-up were published for these studies. In the RESONATE-2 trial, 269 patients 65 years of age or older were randomized to receive ibrutinib or the chemotherapy agent chlorambucil. Patients with del17p were excluded. At an extended median follow-up of 7.4 years [
49], the experimental arm showed an increased 7-year PFS of 59% vs 9% [HR 0.154; 95% CI (0.108-0.220)] and an OS benefit despite crossover to ibrutinib at progression in the chlorambucil arm, with a median OS not reached vs 89 months [HR 0.453, 95% CI (0.276–0.743)]. The benefit of ibrutinib was consistent across all subgroups and there was no significant difference in PFS in the ibrutinib arm in patients <70 or ≥70 years. Ibrutinib was well tolerated, with a median duration of treatment of 74 months and 42% of patients on ibrutinib with up to 8 years of follow-up. The most frequent all-grade adverse events (AEs) with ibrutinib were diarrhea (50%), cough (37%), and fatigue (37%). Most of the ibrutinib associated AEs decreased over time, with the exception of hypertension, which showed prevalence rates of 25%, 23%, and 25% of patients in years 5-6, 6-7, and 7-8, respectively [
49]. Grade ≥3 atrial fibrillation (AFib), grade 3 major hemorrhage and cardiac fatal events occurred respectively in 6%, 7% and 3% of patients in the experimental arm [
49]. Grade ≥3 infections with ibrutinib occurred in 23% of patients at a median follow-up of 29 months [
50]. Ibrutinib was discontinued because of AEs in 24% of patients and 23% required a dose reduction because of AEs. Noteworthy, greater quality of life (QOL) improvements were recorded with ibrutinib as compared with chlorambucil in Functional Assessment of Chronic Illness Therapy-Fatigue. However clinically meaningful improvements, though occurring more frequently with ibrutinib than chlorambucil, did not reach statistical significance [
50].
The Alliance trial (A041202) randomized 547 untreated CLL older patients (65 years of age or older) to receive ibrutinib (I), ibrutinib with rituximab (I+R) or BR [
21]. Patients with del(17p) were included. With a median follow-up of 55 months [
51], the estimated 48-month PFS was 76% in both I containing arms as compared with 47% in the BR arm and 48-month OS estimates were 85% in the I arm, 86% in I+R and 84%, BR arms. Adverse events of clinical interest with ibrutinib included all grade Afib in 19% of the patients as compared with 6% in the BR arm. All grade hypertension was recorded in 73% of the patients on ibrutinib and in 54% of the patients on BR. Interestingly the AE score was higher in the CIT arm for the first 6 cycles than in the ibrutinib containing arms, whereas it was lower with BR when comparing the entire duration of assessment. This observation should be interpreted with caution because only unsolicited, treatment-related grade 1–2 and all-cause grade 3–4 AEs were captured for patients in observation after BR [
52].
The iLLUMINATE trial compared ibrutinib plus obinutuzumab (I+O) to Chlor+O, in 229 patients older than 65 years, or younger with comorbidities as assessed by a CIRS score≥6 [
22]. A clear PFS advantage was documented in the I+O arm as compared with the Chlor+O arm, with an estimated 42-month PFS of 74% Vs 33% and with a 75% reduction in the risk of disease progression or death (HR 0.25; 95% CI: 0.16-0.39; p<0.0001). Interestingly, a significant PFS advantage in the I+O arm was also noted among patients with a favorable immunogenetic profile, i.e., with a mutated status of the immunoglobulin heavy chain gene (M-IGHV) (HR: 0.20; 95% CI: 0.07-0.59). Moreover patient with or without TP53 aberration (del17p or TP53 mutation) had a similar PFS (HR 0.9) in the experimental arm [
22].
Acalabrutinib is a second generation BTKi, characterized by a greater specificity for BTK with fewer off-target effects [
53].
ELEVATE-TN is a phase III randomized trial that enrolled 535 untreated patients ≥65 years or younger with creatinine clearance of 30–69 mL/min or CIRS >6 [
24]. The experimental arms were acalabrutinib with obinutuzumab (A+O) or without (A) and the control arm was Chlor+O. At a median follow up of 46.9 months [
14] a PFS of 87%, 78% and 25% was reported in the A+O, A and Chlor+O arms, respectively. The addition of obinutuzumab to acalabrutinib was associated with a significant prolongation of PFS as compared with A alone (p=0.0296). In the subgroup of patients with TP53 aberration (del17p and/or TP53 mutation) the estimated 4-year PFS was 75% in both acalabrutinib containing arms. IGHV mutational status was not predictive of an inferior PFS in patients treated with A and A+O. Median OS was not reached in all treatment arms and no survival advantage was observed in the experimental arms as compared with the CIT arm. Acalabrutinib-containing arms were associated with a higher incidence of all-grade headache, diarrhea, fatigue, arthralgia, cough, and upper respiratory tract infection. At a 4-year follow-up, grade ≥3 infections occurred in 23.6% patients in the A+O arm, in 16.2% patients in the A arm and in 8.3% in the Chlor+O arm. The incidence of any grade AFib and hypertension was 3.9%/7.9% and 6.1%/7.3% in patients exposed to A+O and A, respectively, as compared with a 0.6%/4.1% in the Chol+O arm. Although cross-trial comparisons should be interpreted with caution it is worth noting that these data on the incidence of cardiovascular events with acalabrutinib compare favorably with those reported in ibrutinib trials and that a head-to head comparison of acalabrutinib and ibrutinib in the relapsed/refractory setting showed a better tolerability profile in the acalabrutinib arm [
54]. At a 4-year follow-up, SPM, including non-melanoma skin cancer were reported in 15.7%, 13% and 4.1% of patients respectively treated with A+O, A and Chlor+O [
14].
Zanubrutinib is a second generation BTKi, that was tested in treatment naïve CLL in the SEQUOIA trial [
15]. Patients enrolled were older (>65 years) or younger with comorbidities (CIRS >6, creatinine clearance <70 mL/min, history of severe or frequent infections which rendered them unsuitable for FCR [
15]. Patients without del17p were randomized to receive zanubrutinib (group A) or BR (group B), while patients with del17p were enrolled in the non-randomized group C.
In 479 patients randomized to zanubrutinib or BR the ORR was 95% Vs 85% respectively. The experimental arm showed a significant prolongation of the 24-month PFS (85.5% Vs 69.5%) and a PFS advantage in the subgroup of M-IGHV became apparent in a recent updated report with median follow-up of 43.7 months [
55]. Median OS was not reached in both groups. Grade ≥3 AE and discontinuations due to AE were reported more frequently in the BR arm than in the zanubrutinib arm (79.7%/13.7% Vs 52.5%/ 8.3%). A 5% and 14.2 incidence of major bleeding and hypertension were reported in the zanubrutinib arm at a median follow-up of 26.2 months and, interestingly, any grade Afib was reported in 3% of the cases in the zanubrutinib arm and in the BR arm [
15].
In group C, 109 patients with del17p and a median age of 70 (range 66–74) were treated with zanubrutinib single agent. The ORR was 94.5%. The estimated PFS at 18-month was 88.6%, with an OS of 95.1%. Safety data were consistent with those reported in previous studies of zanubrutinib. Clinically relevant AEs were AFib in 2.8% of patients, major bleeding in 5.6% with no central nervous system events [
56]. Other cancers were reported in 13%, 9% and 22% of patients in group A, B and C; it is worth noting that in group C 10.8% of cancer were basal cell carcinoma of the skin [
15].
4.2. The BCL-2 Inhibitor Venetoclax
BCL-2, a negative regulator of the mitochondrial pathway of apoptosis, was found to be upregulated in CLL as a consequence of chromosome 13q deletion causing loss of the negative regulatory miRNA-15a/16-1 [
57]. Venetoclax is the first BCL2 inhibitor and was approved by FDA and EMA for the treatment of CLL following the publication of studies that showed its efficacy in CLL with 17p- [
58], in relapsed/refractory CLL [
59] and in treatment naïve CLL [
20].
The CLL 14 study is a phase III trial that enrolled 432 previously untreated patients with a median age of 72 years. The patients had coexisting comorbidities as defined by CIRS >6 and/or CrCl <70 mL/min [
20]. The patients were randomized to receive venetoclax and obinutuzumab (V+O) or Chlor+O. A higher ORR was obtained with V+O (84.7%, including 49.5% CR) as compared with Chlor+O (71.2% including 48.1% CR) [
16]. At a median follow-up of 65.4 months PFS was longer in V+O arm than in the Chlor+O arm ([HR] 0.35 [95% CI 0.26–0.46]) and the estimated PFS rate at 5 years after randomization was 62.6% after V+O and 27.0% after Chlor+O [
60]. The PFS benefit provided by venetoclax was independent from IGHV mutational status and TP53 disruption. Interestingly, a longer PFS was observed with V+O as compared with Chlor+O both in the IGHV unmutated subset (HR 0.25; 95% CI, 0.17 to 0.37; P<.0001) and in the IGHV mutated subset (HR 0.36;95% CI, 0.19 to 0.68; P = .002) [
16]. However, it is worth noting that PFS in both arms was shorter in high-risk subsets, as defined by TP53 disruption and IGHV unmutated. No significant difference in OS was detected at last follow up [
60].
Fixed duration therapy with V+O and Chlor+ O produced deep responses with undetectable minimal residual disease (MRD), which represents a prognostic factor predictive for a longer for progression-free survival (PFS) [
10,
61].
In CLL 14 MRD was measured in peripheral blood (PB) and bone marrow (BM) by an allele-specific oligonucleotide polymerase chain reaction (ASO-PCR), with a cutoff for undetectable MRD (uMRD) at 10−4 [
16]. A higher percentage of patients attained an uMRD in PB at the end of treatment (EoT) in the V+O arm (75%) than in the Chlor+O arm (35.2%, P<0.001). Likewise, a higher fraction of patients was shown to attain uMRD in the BM in the V+O arm (56.9%) as compared with the Chlo+O arm (17.1%) (P<0.001). The duration of uMRD status was longer in the V+O arm than in the Chlor+O arm, with a median time to reach a detectable MRD at 10
-2 of 1,259 days vs 233 days (P <.0001). Interestingly, univariate and multivariate analysis for MRD conversion by NGS from <10
-4 at the end of treatment to ≥10
-4 in the whole cohort showed that age ≥75 years had no impact on the duration of uMRD [
16].
Treatment discontinuation due to AEs occurred in 16.0% and 15.4% of patients in the V+O arm and Chlor+O arm, respectively [
16]. The most common grade≥ 3 AEs was neutropenia, 52.8% in former arm vs 48.1 in latter arm. With grade ≥ 3 infection rate of 17.5% with the V+O arm and a 15.0% rate with the Chlor+O arm, the treatment proved to be well tolerated in this elderly patient population which showed a non-significant increase in the incidence of SPM in the V+O arm (12.7%) as compared with the Chlor+O arm (7.5%) (p=0.074) [
60]. A summary of AE of clinical interest with venetoclax containing regimens is shown in Table 3.
Table 3.
Grade ≥3 adverse events of clinical interest with venetoclax containing regimes in phase-3 clinical trials in older patients.
Table 3.
Grade ≥3 adverse events of clinical interest with venetoclax containing regimes in phase-3 clinical trials in older patients.
Trial |
Median Follow-Up (months) |
Infusion Related Reactions
|
Tumor Lysis Syndrome |
Neutropenia |
Infections |
Afib* |
Reference |
CLL14 |
28.1 |
V+O 9% Chlor+O 10.3% |
V+O 0.5% Chlor+O 1.9% |
V+O 52.8% Chlor+O 48.1% |
V+O 17.5% Chlor+O 15.0% |
NA |
20 |
GLOW |
27.7 |
NA |
Ibr+V 0% Chlor+O 5.7% |
Ibr+V 34.9% Chlor+O 49.5% |
Ibr+V 12.3% Chlor+O 8.6% |
Ibr+V^ 14%/6% Chlor+O 1.9%0%
|
23 |
A prespecified secondary endpoint of CLL14 was represented by the evaluation of health-related QOL and the burden of CLL-specific symptom severity, based on the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 (EORTC QLQ-C30) and the MD Anderson Symptom Inventory (MDASI) with the CLL module (MDASI-CLL). In the V+O arm a relevant improvement of general health status and QOL was recorded at cycle 3, whereas improvement was delayed until cycle 8 with Chlor+O. CLL related symptoms (measured with MDASI-CLL) were similar between the two arms and they remained low during treatment and follow up. The authors concluded that treatment with venetoclax-obinutuzumab was associated with an earlier improvement compared to control arm and that no negative signals on QOL with the V+O regimen were observed [
62].
4.3. Combination Therapy
Ibrutinib and venetoclax exert a preferential anti-leukemic activity in different anatomic compartments. Ibrutinib induces a rapid shrinkage of lymphadenopathy, while venetoclax leads to a rapid clearance of peripheral blood. In ex vivo model of CLL, Pin Lu et al., demonstrated that ibrutinib inactivated a subpopulation of CLL cells more frequently encountered in the proliferation centers of the lymph nodes, whereas venetoclax was able to induce the cell death of resting CLL cells especially in peripheral blood [
63]. Moreover, BTK inhibition was shown to enhance mitochondrial BCL2 dependence of CLL cells, favoring the killing by venetoclax [
64]. Based on these biologic data, trials combining a BTKi and venetoclax were designed, showing high efficacy of this combination in all age groups [
23,
65,
66,
67].
In the GLOW trial, that included older patients (>65 years) and/or patients with comorbidities, i.e., with CIRS>6 or creatinine clearance <70 mL/min) [
23], 210 untreated CLL patients were randomized to receive 3 months of lead-in ibrutinib followed by 12 months of ibrutinib and venetoclax (I+V) or Chlor+O (6 cycles). Patients with TP53 disruption were excluded. A similar ORR was observed (86.8% with I+V and 84.8% with Chlor+O), but CR rates were higher with I+V (38.7% Vs 11.4%). Interestingly, uMRD at end of treatment was observed in the PB and BM in the I+V arm (54.7% and 51.9%, respectively). With a median follow-up of 27.7 months, PFS was longer with for I+V than with Chlor+O (hazard ratio, 0.216; 95% confidence interval 0.131-0.357; P<.001), with an estimated 24-month PFS rate of 84.4% with I+V vs 44.1% with Chlor+O. The PFS advantage was evident across all the specified subgroups, including patients ≥65 years. With a median follow up of 34.1 months, OS was not significantly different in the two arms.
AE events of clinical interest with I+V are summarized in Table 3. The overall incidence of grade≥3 AEs was similar in the 2 arms (75.5% and 69.5% of patients in the I+V arm and Chlor+O arm, respectively). The administration of 3 cycles of ibrutinib prior to venetoclax reduced the number of patients at high risk of tumor lysis syndrome (TLS) (1.9% vs 24.5% at baseline) and no case of TLS occurred in the I+V arm. SPM were reported in 7.5% and 9.5% of patients treated respectively in the I+V and Chlor+O arms. The overall number of deaths at the primary analysis was similar for the two arms, however I+V was associated with four cardiac/sudden deaths that occurred in patients with higher CIRS and ECOG PS score, underlining the importance of a complete cardiologic assessment before ibrutinib based treatment [
23].