Abstract
Importance
The Bruton’s Tyrosine Kinase inhibitor ibrutinib is effective in patients with chronic lymphocytic leukemia (CLL). Reasons for discontinuation from this drug and outcomes following discontinuation have not been evaluated outside of clinical trials with relatively short follow-up.
Objective
To determine features associated with discontinuation of ibrutinib and outcomes.
Design
308 patients participating in four sequential trials of ibrutinib were included. These trials accrued patients included in this analysis from May 2010 until April 2014, and data were locked in June 2014.
Setting
The Ohio State University Comprehensive Cancer Center
Participants
Patients with CLL enrolled on 4 sequential clinical trials.
Main Outcome Measure
Patients were evaluated for time to discontinuation, reasons for discontinuation, and survival following discontinuation. For patients who discontinued due to progression, targeted deep sequencing was performed in samples at baseline and relapse.
Results
With a median follow-up of 20 months, 232 patients remain on therapy, 31 have discontinued because of progression, and 45 have discontinued for other reasons. Disease progression includes Richter’s transformation or progressive CLL. Richter’s appeared to occur early and CLL progressions later (cumulative incidence at 12 months: 4.5% (95% CI: 2.0% to 7.0%) and 0.3% (95% CI: 0% to 1.0%), respectively). Median survival following Richter’s transformation was 3.5 months (95% CI: 0.3–6.0), and 17.6 months (95% CI: 4.7-not reached) following CLL progression. Sequencing on peripheral blood from 8 patients with Richter’s transformation revealed 2 with mutations in BTK, and a lymph node sample showed no mutations in BTK or PLCγ2. Deep sequencing on 11 patients with CLL progression revealed BTK or PLCγ2 mutations in all. These mutations were not identified pre-treatment in any patient.
Conclusions and Relevance
This single institution experience with ibrutinib confirms it to be an effective therapy and identifies, for the first time, baseline factors associated with ibrutinib discontinuation. Outcomes data show poor prognosis after discontinuation, especially for those patients with Richter’s transformation. Finally, sequencing data confirm initial reports associating mutations in BTK and PLCγ2 with progression and clearly show that CLL progressions are associated with these mutations, while Richter’s transformation is likely not.
Introduction
Chronic lymphocytic leukemia (CLL) is the most prevalent leukemia in adults and is not considered curable outside of allogeneic stem cell transplantation. Significant advances have been made in the therapy, notably the emergence of kinase inhibitors for patients with relapsed disease. Prior to FDA approval of ibrutinib and idelalisib with rituximab, standard therapy for relapsed CLL could be expected to induce response rates of 30–50%1–3 and progression free survival (PFS) of generally less than 1 year. The Phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3 kinase) delta isoform inhibitor idelalisib4,5 and Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib have dramatically changed outcome for these patients.
BTK is a critical kinase in the B cell receptor signaling pathway. This pathway is amplified in CLL and results in amplification of proliferation and anti-apoptotic signals.6–9 By inhibiting BTK, ibrutinib eliminates the activation of these pro-survival pathways8 and microenvironment survival signals.8,10 In patients, this translates into high clinical response rates and durable remissions. The Phase I trial of ibrutinib in relapsed B cell malignancies showed activity in a variety of diseases,11 and the benefit in CLL has been confirmed in Phase Ib/II12,13 and Phase III trials14 of ibrutinib as a single agent. In the Phase III RESONATE study, ibrutinib was compared with ofatumumab. With a median follow-up of 9.4 months, overall response (ORR) was superior with ibrutinib, but more importantly both PFS (median 8.1 months for ofatumumab vs not reached for ibrutinib) and overall survival (OS) (12-month estimates: 81% for ofatumumab, 90% for ibrutinib) were significantly improved with ibrutinib.14 The OS benefit is particularly impressive considering that follow-up was short, and 14 months following the beginning of enrollment, patients who progressed on ofatumumab were allowed to cross over to ibrutinib.
Ibrutinib has also been studied in combination with chemotherapy and immunotherapy. While laboratory data suggested that combination with CD20 antibodies may be less effective because of ITK inhibition15 which impairs NK cell ADCC16, trials of ibrutinib in combination with rituximab17 and ofatumumab18 have shown similarly impressive efficacy. It is yet to be determined whether a combination of ibrutinib with another active agent is superior to single agent ibrutinib. While response to ibrutinib has been high with therapy well-tolerated overall, some patients have relapsed while others have been taken off therapy for toxicity or other reasons. Our group and others have shown that relapse in CLL can be mediated by at least two separate mechanisms.19 One is by mutations in BTK which both decrease ibrutinib’s affinity for BTK and also changes the binding from irreversible to reversible. The other is through a variety of mutations in PLCγ2, the immediate downstream target of BTK. We have identified a number of mutations in PLCγ2 which are potentially gain of function and likely serve to allow the cell an ability to signal in the presence of ibrutinib. Herein, we describe the characteristics of patients who discontinue ibrutinib for relapse and non-relapse reasons, identify factors which may contribute to discontinuation, perform deep sequencing for known resistance mutations, and describe outcomes of patients after ibrutinib discontinuation.
Patients and Methods
Patients, Treatment Regimens, and Definitions of Clinical Endpoints
All patients at The Ohio State University Comprehensive Cancer Center who were enrolled on four sequential trials of ibrutinib in patients with CLL were included in this analysis. Study designs are outlined in Table 1. OSU 10032 (PCYC 1102) was a multi-institutional Phase Ib/II study of single agent ibrutinib in patients with relapsed/refractory or treatment naïve CLL. OSU 10053 (PCYC 1109) was a single institution Phase Ib/II study of ibrutinib in combination with ofatumumab in patients with relapsed/refractory CLL. OSU 11133 was a single institution Phase II study of single agent ibrutinib in patients with relapsed/refractory CLL. OSU 12024 (RESONATE) was a multi-institutional Phase III study of single agent ibrutinib vs ofatumumab in patients with relapsed/refractory CLL. From this study, all patients initially assigned to ibrutinib or who crossed over to ibrutinib following progression with ofatumumab were included. All patients participating in these institutional review board approved clinical studies signed written informed consent.
Table 1.
Studies Included in Analysis
| Study | Number of Patients |
Duration of Enrollment |
Patient Population |
Study Drug Schedule |
|---|---|---|---|---|
| OSU 10032 (PCYC 1102) | 50 | 7/20/10–3/19/12 | Relapsed or Refractory CLL/SLL (N=42) Untreated CLL/SLL (N=8) |
Ibrutinib 420 or 840 mg daily until disease progression |
| OSU 10053 (PCYC 1109) | 71 | 1/26/11–6/12/12 | Relapsed or Refractory CLL/SLL | Cohort 1: Ibrutinib 420 mg daily starting C1D1 until disease progression; Ofatumumab start C2D1 weekly × 8 weeks, then monthly × 4 months Cohort 2: Ibrutinib 420 mg daily starting C1D2 until disease progression; Ofatumumab start C1D1 weekly × 8 weeks, then monthly × 4 months Cohort 3: Ofatumumab start C1D1 weekly × 8 weeks, then monthly × 4 months. Ibrutinib start C3D1daily until disease progression. |
| OSU 11133 | 150 | 5/30/12–4/8/14 | Relapsed or Refractory CLL/SLL | Ibrutinib 420 mg daily until disease progression |
| OSU 12024 (RESONATE) | 37 | 7/31/12–3/10/14 | Relapsed or Refractory CLL/SLL | Ibrutinib 420 mg daily until disease progression |
Ion Torrent Deep Sequencing
DNA was extracted from cryopreserved cells using QIAmp DNA Mini kit (Qiagen; Hilden, Germany). BTK and PLCγ2 genes were analyzed using the Ion Torrent platform from Life Technologies (Carlsbad, CA). Details regarding library generation and sequencing can be found in the Supplemental eMethods.
Statistical Considerations
Time to discontinuation of treatment was measured from the first date of treatment with ibrutinib until the date off-study, censoring patients who had not discontinued ibrutinib at the date of last contact; patients who went off study for transplant or continued treatment elsewhere (n=7) were censored at that time. Median follow-up was calculated among all patients (n=232) censored for time to discontinuation of treatment. Fine and Gray models of cumulative incidence20,21 were fit to identify variables associated with a particular failure type and in the presence of competing risks. Multivariable models of cumulative incidence were fit using forward selection, with variables no longer entering the model if p>0.05, unless deemed clinically important. All models were adjusted for monotherapy with ibrutinib versus combination therapy with ibrutinib and ofatumumab; other variables considered included age, sex, number of prior therapies, baseline LDH, FISH abnormalities del(17p), del(11q), trisomy 12, del(13q), MYC abnormalities and BCL6 abnormalities, as well as complex karyotype and IGHV mutational status. Survival following discontinuation was calculated from the date off study until the date of death from any cause, censoring patients at last contact. Survival estimates were calculated by the method of Kaplan-Meier and differences between curves were tested with the log-rank test. All tests were two-sided and statistical significance was declared at α=0.05. The cmprsk package within TIBCO Spotfire S+ Version 8.2 was used to analyze time-to-event data in the presence of competing risks, whereas SAS statistical software Version 9.3 (SAS, Cary, NC, USA) was used for all other data analyses.
Results
Patient Characteristics and Rate of Ibrutinib Discontinuation
A total of 308 patients were included in this analysis, with data locked as of June 9, 2014. This includes 237 patients treated with single agent ibrutinib on 3 clinical trials, and 71 patients treated with ibrutinib in combination with ofatumumab. Clinical characteristics for all patients can be found in Table 2. Three patients treated with ibrutinib plus ofatumumab had active Richter’s transformation at study entry. Patients were generally high risk, with a median of 3 prior therapies (range 0–16; 8 patients were previously untreated), 80% with unmutated IGHV, 58% with complex karyotype (3 or more distinct abnormalities), 37% with del(17p13.1), and 26% with del(11q22.3). With a median follow-up of 20 months (range 2–47), 232 patients (75%) remain on therapy, including 7 patients who were removed from study to pursue stem cell transplantation or to receive ibrutinib therapy commercially at another center. Of the 76 patients who discontinued therapy, only 31 (10% of 308 total) discontinued due to disease progression.
Table 2.
Clinical Characteristics
| Characteristic | Total (n = 308) |
|
|---|---|---|
| Study, num. (%) | ||
| OSU-10032 | 50 (16) | |
| OSU-10053 | 71 (23) | |
| OSU-11133 | 150 (49) | |
| OSU-12024 | 37 (12) | |
| Median Age, yrs (Range) | 65 (26–91) | |
| Number Male, (%) | 217 (70) | |
| Rai Stage, num. (%) | ||
| 0 | 11 (4) | |
| I | 69 (22) | |
| II | 22 (7) | |
| III | 44 (14) | |
| IV | 162 (53) | |
| Median Number of Prior Therapies (Range) | 3 (0–16) | |
| Median LDH U/L (Range) | 218 (96–1485) | |
| 8 unknown | ||
| FISH Abnormalities*, num. (%) | ||
| Del(17p) | 113 (37) | |
| Del(11q) | 80 (26) | |
| Trisomy 12 | 53 (17) | |
| Del(13q) | 156 (51) | |
| MYC abnormality | 64 (21) | |
| BCL6 abnormality | 26 (9) | |
| 3–6 unknown | ||
| Complex Cytogenetics (≥3 abnormalities), num. (%) | 169 (58) | |
| 15 unknown | ||
| IGHV Unmutated, num. (%) | 219 (80) | |
| 34 unknown | ||
FISH Abnormalities are not mutually exclusive.
Non-relapse discontinuation
Forty-five patients discontinued therapy for reasons other than disease progression. Twenty-eight discontinued because of infection, 8 due to other adverse events, and 9 due to other events including progressive multifocal leukoencephalopathy in one who received rituximab 363 days prior, medication noncompliance, comorbid medical condition (n=2), failure to thrive, sudden cardiac death, need for anticoagulation (n=2), and cerebrovascular event. Non-relapse discontinuations tended to occur early, with only 1 patient discontinuing therapy after 24 months for a reason other than progressive disease. Therapy limiting infections especially tended to occur early, with a median time to discontinuation of 102 days. Sixteen discontinuations due to infectious toxicity occurred during the first 6 months of therapy, 7 within 6–12 months, and 5 beyond 12 months.
Using multivariable modeling, age was the only significant independent risk factor of therapy discontinuation for reason other than disease progression (hazard ratio (HR) for 10-year increase 1.87; 95% confidence interval (CI): 1.33–2.64, p<0.001; Table 3). Increasing number of prior therapies was also associated with non-relapse discontinuation although it was not statistically significant (HR 1.09, 95% CI: 1.00–1.19, p=0.054).
Table 3.
Multivariable Models for Cumulative Incidence of Two Failure Types: Disease Progression and Toxicity, Adjusted for Monotherapy
| Variable | Event=Progression | Event=Toxicity |
|---|---|---|
| HR (95% CI)/P | HR (95% CI)/P | |
| Age, 10 year increase | — | 1.87 (1.33, 2.64) / <0.001 |
| Number of Prior Treatments, 1 unit increase | — | 1.09 (1.00, 1.19) / 0.054 |
| BCL6 abnormality, Yes vs. No | 2.70 (1.25, 5.85) / 0.012 | — |
| Complex Karyotype, Yes vs. No | 4.47 (1.50, 13.34) / 0.007 | — |
A hazard ratio > 1 (< 1) indicates a higher (lower) risk of an event for the first category listed for dichotomous variables or increasing values of continuous variables.
Patients who discontinued ibrutinib therapy for non-relapse reasons tended to do poorly, with a median survival after discontinuation of 8 days (95% CI: 0 to 56). This was heavily influenced by patients coming off trial for infection, where 16 of the 28 patients with infection expired the same day they came off treatment, and only two were alive at last follow-up on days 63 and 176. Conversely, patients who discontinued therapy for non-infectious adverse events or other reasons had a median survival of 238 days, where 7 of the 17 patients had not expired at last follow-up, and 4 had survived more than a year following treatment discontinuation (eFigure 1).
Discontinuation due to disease progression
Of 31 patients who discontinued therapy due to disease progression, 13 progressed with CLL and 18 with Richter’s transformation, three of whom had previously transformed. Characteristics of these patients are listed in Table 4. While most of the patients with Richter’s developed diffuse large B cell lymphoma (78%), one patient each developed Hodgkin lymphoma, plasmablastic lymphoma, composite B and T cell lymphoma, and peripheral T cell lymphoma. Richter’s transformation tended to occur earlier than progressive disease due to CLL, where the estimated cumulative incidence of Richter’s transformation at 12 months was 4.5% (95% CI: 2.0% to 7.0%) and the estimated cumulative incidence of progressive disease due to CLL at 12 months was 0.3% (95% CI: 0% to 1.0%) (Figure 1).
Table 4.
Characteristics of Patients who Relapse During Ibrutinib Therapy
| Type of Relapse |
Monotherapy vs Combination with Ofatumumab |
Baseline FISH, complexity of karyotype |
Days on Study |
Primary Site of Relapse |
Time from Ibrutinib Discontinuation Until Next Therapy |
|---|---|---|---|---|---|
| DLBCL | Monotherapy | del(17p), del(13q), MYC; complex | 26 | LN | 18 |
| DLBCL | Monotherapy | del(17p), del(11q), MYC, BCL6; complex | 55 | LN | 21 |
| DLBCL | Monotherapy | del(13q), MYC; complex | 125 | LN | 21 |
| DLBCL | Monotherapy | del(17p), +12; complex | 170 | LN | No treatment |
| DLBCL | Monotherapy | Normal FISH; complex | 231 | LN | 7 |
| DLBCL | Monotherapy | del(17p), +12, MYC; complex | 261 | LN | No treatment |
| DLBCL | Monotherapy | del(11q), MYC; complex | 271 | LN | 1 |
| DLBCL | Monotherapy | del(17p), del(11q), +12, MYC, BCL6; complex | 309 | LN | 1 |
| DLBCL | Monotherapy | unknown | 387 | LN | 24 |
| DLBCL | Combination | del(17p); complex | 429 | LN, peripheral blood (CLL) | No treatment |
| DLBCL | Monotherapy | del(17p), del(13q); complex | 562 | LN | No treatment |
| DLBCL | Monotherapy | del(17p), MYC, BCL6; complex | 785 | LN, peripheral blood (CLL) | 12 |
| DLBCL progression** | Combination | del(13q), MYC; complex | 479 | LN | 11 |
| DLBCL progression** | Combination | BCL6; complex | 168 | LN | 33 |
| Composite B&T Cell Lymphoma | Combination | +12, del(13q); Not complex | 377 | LN | No treatment |
| Hodgkin lymphoma | Monotherapy | del(17p), del(11q), del(13q); complex | 308 | LN | 44 |
| Plasmablastic Lymphoma | Monotherapy | del(11q), del(13q); not complex | 337 | LN | 21 |
| Peripheral T Cell Lymphoma | Monotherapy | Normal FISH; unknown | 33 | LN | No treatment |
| CLL | Monotherapy | del(13q); complex | 474 | LN, peripheral blood | 1 |
| CLL | Monotherapy | Normal FISH; complex | 511 | LN, peripheral blood | 12 |
| CLL | Monotherapy* | del(11q), BCL6; complex | 664 | Peripheral blood | 21 |
| CLL | Monotherapy | del(17p), MYC; complex | 965 | LN, peripheral blood | 8 |
| CLL | Monotherapy | del(11q); not complex | 1119 | LN, peripheral blood | 2 |
| CLL | Monotherapy | del(17p), del(13q), MYC, BCL6; complex | 1216 | LN, peripheral blood | 29 |
| CLL | Monotherapy | del(17p); complex | 1295 | LN only | 1 |
| CLL | Combination | del(11q), del(13q); not complex | 115 | Ascites | 16 |
| CLL | Combination | del(17p); complex | 426 | unknown | Unknown |
| CLL | Combination* | del(17p); complex | 505 | Peripheral blood | 2 |
| CLL | Combination* | Normal FISH; Complex | 673 | LN only | 42 |
| CLL | Combination | del(17p), del(13q), MYC; complex | 693 | LN, peripheral blood | 17 |
| CLL | Combination | del(17p), del(13q), MYC, BCL6; complex | 1034 | LN only | 1 |
Patients previously reported19
Patients with history of Richter’s transformation at study entry
Figure 1. Cumulative Incidence of Discontinuation of Ibrutinib Therapy.
Rate of discontinuation is low overall, with relapse-related discontinuations less frequent than non-relapse. Richter’s transformation tends to occur earlier than progression with typical CLL (A). (B) shows close-up curves to highlight differences in discontinuation patterns between CLL progression, Richter’s transformation, and other events.
Due to the low frequency of relapse, failures due to Richter’s transformation or CLL were combined in an attempt to identify baseline factors that increased risk of disease progression. In modeling individual variables associated with disease-related discontinuation and adjusting for monotherapy with ibrutinib, increased number of prior therapies (HR 1.12) BCL6 abnormalities (HR 3.77), MYC abnormalities (HR 2.59), presence of del(17p) (HR 2.28), and complex karyotype (HR 5.17) were all significantly associated with a higher risk of progression (eTable 1). In multivariable analysis, presence of BCL6 abnormalities (HR 2.70, 95% CI: 1.25–5.85, p=0.012) and complex karyotype (HR 4.47, 95% CI: 1.50–13.34, p=0.007) remained independent risk factors (Table 3). Increased LDH at baseline was not significantly associated with disease progression when combining failure types, but appeared to be associated with development of Richter’s.
Patients with Richter’s transformation generally did poorly following relapse. Of 18 patients, 6 were unable to receive further therapy and died within 1 month of transformation. One patient was treated at another institution with an unknown regimen. The remaining 11 patients were treated with R-EPOCH (n=6), R-CHOP, R-ICE, rituximab/dexamethasone, OFAR, or brentuximab. One patient was lost to follow-up after treatment was started, but the 10 remaining patients all progressed during their next treatment regimen. Median survival from transformation was 3.5 months (95% CI: 10 days to 6.0 months; eFigure 2).
Patients with CLL progression tended to have rapid disease progression following discontinuation of ibrutinib. One patient had rapid progression of nodes at another facility and was not seen again at OSU, so details of care are unknown. One patient had primarily progression in ascites and cytopenias, so was unmeasurable. Of the remaining 11, 2 had progression in the peripheral blood only, 3 had progression in the nodes only, and 6 had both. For patients with peripheral blood disease (n=8), the median increase in absolute lymphocyte count during the 6 months prior to ibrutinib discontinuation was 17.34×109/L (range 6.62–177.34). All patients had a normal lymphocyte count 6 months prior to discontinuation. For 5 patients where there was a time interval of >1 week between discontinuation of ibrutinib and start of next therapy, the average change in lymphocyte count between relapse and ibrutinib discontinuation was +0.75/day, and was +4.6/day from the time of ibrutinib discontinuation until next therapy. For the patients with nodal disease (n=9), the median increase in the sum of the products of lymph node diameter of the 3 largest nodes on CT scan was 10.85 cm (range 3.98–104.15). Three patients had palpable lymph nodes and a time of >1 week between ibrutinib discontinuation and next therapy. In these patients, the rate of change of the sum of the products of the 3 largest lymph nodes by physical exam was +0.35, 0, and 0.2 cm per day respectively prior to ibrutinib discontinuation, and +0.79, 1.18, and 4.63 cm per day after ibrutinib discontinuation.
After progression, patients tended to require the initiation of therapy quickly in order to achieve disease control (Table 4). Of the 13 patients, 11 received further therapy, most within a few weeks of discontinuing ibrutinib (median 10 days, range 1 to 42). Two were not able to receive further therapy and died at day 10 and 180, respectively, following discontinuation. Median survival from time of CLL progression was 17.6 months (95% CI: 4.7 to not reached; eFigure 2).
Association of BTK and PLCγ2 mutations with relapse on ibrutinib
We have previously shown that resistance to ibrutinib can be mediated through mutations in BTK or PLCγ2 in a small group of patients. To extend these findings, we have performed Ion Torrent deep sequencing for both of these genes at baseline and time of relapse for patients who have relapsed on ibrutinib (Table 5).
Table 5.
Ion Torrent Deep Sequencing of 13 Patients who have Relapsed on Ibrutinib in which Mutations have been Identified in BTK or PLCγ2*
| Baseline | Relapse | |||||||
|---|---|---|---|---|---|---|---|---|
| Patient | Type of Relapse |
Chromosome | Gene | AA change |
Coverage | Variant Frequency (%) |
Coverage | Variant Frequency (%) |
| 1 | CLL | 16 | PLCγ2 | R665W | 870 | 0 | 9977 | 5.5 |
| 16 | PLCγ2 | S707P | 2940 | 0 | 9980 | 5.3 | ||
| 16 | PLCγ2 | S707F | 2937 | 0 | 9996 | 3.3 | ||
| 16 | PLCγ2 | R742P | 1623 | 0 | 9987 | 6.1 | ||
| 16 | PLCγ2 | L845fs | 1200 | 0 | 5436 | 14.9 | ||
| 2 | CLL | 16 | PLCγ2 | R665W | 3230 | 0 | 9252 | 45 |
| 3 | CLL | X | BTK | C481F | 1837 | 0 | 6687 | 84 |
| 4 | CLL | X | BTK | C481S | 2730 | 0 | 4417 | 16.9 |
| 5 | CLL | 16 | PLCγ2 | R665W | 3465 | 0 | 2781 | 2 |
| 16 | PLCγ2 | S707Y | 8456 | 0 | 2346 | 6.6 | ||
| 16 | PLCγ2 | L845F | 3431 | 0 | 1025 | 23.8 | ||
| X | BTK | C481S | 875 | 0 | 2429 | 6.8 | ||
| 6 | CLL | X | BTK | C481S | 2086 | 0 | 5903 | 37.8 |
| 7 | CLL | X | BTK | C481S | 4453 | 0 | 490 | 47.5 |
| 8 | CLL | X | BTK | C481S | 1210 | 0 | 2689 | 74.7 |
| 9 | CLL | X | BTK | C481S | 2260 | 0 | 8699 | 6 |
| 10 | CLL | 16 | PLCγ2 | D1140G | 1372 | 0 | 5974 | 13.5 |
| X | BTK | C481S | 3109 | 0 | 6941 | 13 | ||
| 11 | CLL | X | BTK | C481S | 1119 | 0 | 4638 | 5.4/3.4** |
| 12 | Richter | X | BTK | C481S | 1622 | 0 | 497 | 51.9 |
| X | BTK | T474I | 264 | 0 | 112 | 4 | ||
| X | BTK | T474S | 264 | 0 | 112 | 4 | ||
| 13 | Richter | 16 | PLCγ2 | D334H | 629 | 0 | 27622 | 5.7 |
| X | BTK | C481Y | 487 | 0 | 16800 | 28.7 | ||
| X | BTK | C481R | 488 | 0 | 17699 | 24.2 | ||
| X | BTK | L528W | 310 | 0 | 9994 | 7.9 | ||
7 patients with Richter’s transformation did not have mutations identified in BTK or PLCγ2 with similarly deep coverage and are not included
Patient with 2 different allelic mutations with both resulted in C481S
In patients who progressed with Richter’s, peripheral blood was obtained at baseline and time of relapse in 8, whereas lymph node biopsy was obtained at relapse from 1 patient. The lymph node at progression showed no mutations in BTK or PLCγ2. Peripheral blood in 6 patients at progression was negative for mutations, but two patients had mutations: one had 3 separate mutations in BTK (C481S, T474I, T474S), and one had 3 separate mutations in BTK (C481Y, C481R, L528W) and D334H mutation in PLCγ2. Notably, these two patients were the only Richter’s patients who had a worsening lymphocytosis with CLL phenotype at the same time as Richter’s transformation, so it is possible that they had both progressive CLL as well as Richter’s.
In patients who progressed with CLL, samples at baseline (peripheral blood) and at the time of relapse (peripheral blood in 9, bone marrow in 2) was obtained on 11 of 13. Three of these patients have been previously reported,19 and had acquired mutations in BTK C481S, PLCγ2 R665W, and BTKC481S in association with PLCγ2 R665W, L845F, and S707Y. In the 8 remaining patients, 5 had sole mutations in BTK with C481S, one had BTK C481F mutation, and one had 5 separate mutations in PLCγ2 (R665W, S707P, S707F, R742P, and L845fs). One additional patient had both BTK and PLCγ2 mutations, with BTK C481S and PLCγ2 D1140G. Thus, all patients that have been identified at our institution to have progressive CLL after ibrutinib have had mutations in either BTK or PLCγ2 that were acquired during therapy. Relapse mutations were not identified pre-treatment in any patient with deep sequencing (Table 5).
Discussion
Here we describe the first large single center experience of patients treated with ibrutinib with a median follow-up of almost 2 years. We show that non-relapse discontinuation of therapy is more common early in therapy and becomes progressively infrequent. We show that Richter’s transformation and CLL progressions are both relatively uncommon in this very high-risk population, with Richter’s tending to occur earlier, and CLL progressions later. Finally, we confirm and extend our previous findings that CLL progression is associated with mutations in BTK or PLCγ2.
While previous publications of clinical trials report reasons for discontinuation from ibrutinib, this report greatly extends these findings by including a larger number of patients than any individual trial, and longer follow-up than other reports. As well, we report for the first time multivariable analysis identifying factors at baseline that are associated with discontinuation and outcomes following discontinuation from ibrutinib, which will be relevant for general oncology practice.
Perhaps most significant, these data confirm that ibrutinib is a drug capable of shifting the paradigm of therapy for relapsed disease. In our group of high-risk patients, the estimated cumulative incidence of progression at 18 months was only 8.9% (95% CI: 5.2 to 12.6%). As more patients are treated with ibrutinib off-study, we expect that outcomes will not be quite as positive as in clinical trials, given variability in compliance and follow-up, but certainly we will see patients with relapsed CLL living longer than has been seen in the past. As our data show an estimated cumulative incidence of non-relapse discontinuation of 15.6% (95% CI: 11.1 to 20.0%) at 18 months, there remains a need to identify new therapies for patients who do not tolerate ibrutinib or who are unable to continue because of concomitant medications.
These data also confirm and extend earlier reports of the association of BTK and PLCγ2 mutations with CLL relapse. Interestingly, in our experience thus far, these mutations are associated with all CLL relapses. While we have not yet characterized all of these mutations, our research thus far has shown that BTK C481 mutations interfere with ibrutinib binding, and PLCγ2 mutations are potentially gain-of-function. We are currently characterizing the additional mutations identified as part of this analysis. From this small subset of patients, it appears that these mutations may help to identify a patient who is relapsing with CLL. Importantly, we still do not see evidence of these mutations at baseline, suggesting that they are indeed the result of selective pressure from the drug, although sampling only peripheral blood compartment is a limiting factor and it is possible that these mutations may be present in the blood at very low levels or in other niches at baseline. Finally, our data suggest that Richter’s transformation is not associated with these mutations in most cases and opens the question of resistance mechanisms in this patient population.
While this analysis presents data from a large number of patients and we attempt to control for confounding variables through multivariable analyses, our study is limited by the retrospective nature of the data and the single center experience. It is possible that patterns at our institution may not be generalizable to the entire ibrutinib-treated population and it will be important to confirm these findings in larger multi-center patient populations. However, given that this drug is relatively new and discontinuations are infrequent with short follow-up, it will likely be many years before larger series with longer follow-ups are available.
Ultimately, we show that patients who progress while on ibrutinib, especially those with Richter’s transformation, have poor outcomes. While the incidence of progression is low with this duration of follow-up, it is expected that more patients will relapse with extended follow-up. We show that patients tend to progress quickly, especially when the drug is stopped, which points to a need for clinical trials to allow shorter washout periods for these patients. As well, physicians may consider waiting to discontinue ibrutinib until an alternative therapeutic plan can be formed, and potentially even continuing ibrutinib in combination with Richter’s-directed therapy in select patients.
These data show that continued clinical trials are needed in this disease, and that scientific progress cannot stop even with a breakthrough drug like ibrutinib. Patients with Richter’s transformation remain a high research priority to identify new targets and new therapies. As well, the question of whether high risk patients may benefit more from transplant or kinase inhibitor is unanswered. There remains much to be learned about the biology of CLL from kinase inhibitor drugs, and the ideal drug, target, or combination for all patients is likely yet to be identified.
Supplementary Material
Acknowledgements
The authors wish to thank the patients and families who provided samples for this work. This work was supported by a Specialized Center of Research from the Leukemia and Lymphoma Society, P50-CA140158, P01 CA95426, R01 CA177292, and K23 CA178183 from the National Cancer Institute, The D. Warren Brown Foundation, Four Winds Foundation, The Sullivan Chronic Lymphocytic Leukemia Research Fund, Mr. and Mrs. Michael Thomas, Mr. and Mrs. Al Lipkin, The Harry T. Mangurian Jr. Foundation, Pelotonia, and Conquer Cancer Foundation. For OSU 10032, 10053, and 12024, Pharmacyclics, Inc. was involved in the design and conduct of the studies and provided study drug for OSU 11133. Pharmacyclics, Inc. was not involved in data analysis for this manuscript, but did approve the manuscript prior to submission. JAW had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Footnotes
Trial Registration: NCT01105247, NCT01217749, NCT01589302, and NCT01578707
Conflicts of Interest: KJM has received research support and has served as a consultant for Pharmacyclics. KAB has received research funding from Pharmacyclics and Janssen. SMJ has received research funding from Pharmacyclics. JAJ has served as a consultant for Pharmacyclics and Janssen. The remaining authors declare no relevant conflict of interest.
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