Complex karyotype is a stronger predictor than del(17p) for an inferior outcome in relapsed or refractory chronic lymphocytic leukemia patients treated with ibrutinib-based regimens
Philip A. Thompson provided clinical care to patients, collected and analyzed data, performed the statistical analysis, and wrote the article. William G. Wierda, Alessandra Ferrajoli, Susan C. Smith, Zeev Estrov, Nitin Jain, Hagop M. Kantarjian, and Michael J. Keating were involved in the development of critical themes, provided clinical care to patients, and cowrote the article. Francesco Stingo performed the statistical analysis and cowrote the article. Susan M. O'Brien and Jan A. Burger designed clinical studies, were involved in the development of critical themes, provided clinical care to patients, and cowrote the article.
This study was presented in part at the 56th Annual American Society of Hematology Meeting; December 6-9, 2014; San Francisco, CA.
Abstract
BACKGROUND
Ibrutinib is active in patients with relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL). In patients treated with ibrutinib for R/R CLL, del(17p), identified by interphase fluorescence in situ hybridization (FISH), is associated with inferior progression-free survival despite equivalent initial response rates. Del(17p) is frequently associated with a complex metaphase karyotype (CKT); the prognostic significance of CKT in ibrutinib-treated patients has not been reported.
METHODS
This study reviewed 88 patients treated for R/R CLL at The University of Texas MD Anderson Cancer Center with investigational ibrutinib-based regimens from 2010 to 2013. Pretreatment FISH and lipopolysaccharide-stimulated metaphase cytogenetic analysis were performed on bone marrow.
RESULTS
An adequate pretreatment metaphase karyotype was available for 56 of the 88 patients. The karyotype was complex in 21 of the 56 cases; 17 of the 21 had del(17p) according to FISH. The overall response rate, including partial remission with persistent lymphocytosis, was 94%; 18% had complete responses. In a multivariate analysis (MVA), only CKT was significantly associated with event-free survival (EFS; hazard ratio [HR], 6.6 [95% CI 1.7-25.6]; P = .006). Fludarabine-refractory CLL (HR, 6.9 [95% CI 1.8-27.1], P = .005) and CKT (HR 5.9 [95% CI 1.6-22.2], P = .008) were independently associated with inferior overall survival (OS) in MVA. Del(17p) by FISH was not significantly associated with EFS or OS in MVA.
CONCLUSIONS
CKT is a powerful predictor of outcomes for ibrutinib-treated patients with R/R CLL and may be a stronger predictor of biological behavior than del(17p) by FISH. Because of their relatively poor outcomes, patients with CKT are ideal candidates for studies of consolidative treatment strategies or novel treatment combinations. Cancer 2015 © 2015 American Cancer Society. Cancer 2015;121:3612–3621. © 2015 American Cancer Society.
INTRODUCTION
Patients with chronic lymphocytic leukemia (CLL) with del(17p) by fluorescence in situ hybridization (FISH) have poor outcomes when they are treated with chemotherapy or chemoimmunotherapy; the median survival in such patients is approximately 2 years.1 Long-term survival can be achieved with allogeneic stem cell transplantation (allo-SCT) in some patients; with approximately 50% 5-year survival, patients with del(17p) have outcomes similar to those of patients without del(17p) after allo-SCT.2, 3
The Bruton tyrosine kinase (BTK) inhibitor ibrutinib4 is active in relapsed/refractory (R/R) CLL with a progression-free survival (PFS) of approximately 75% at 26 months.4 Patients with del(17p) have PFS inferior to that of patients without del(17p),4 with a median PFS of approximately 28 months.5 Ibrutinib resistance has been associated in some cases with the development of specific mutations in the B-cell receptor signaling pathway, most commonly the C481S mutation in BTK, which prevents irreversible binding of ibrutinib to BTK. Patients with del(17p) and/or a complex metaphase karyotype (CKT) may be more likely to develop these mutations.6 The optimal treatment for patients refractory to ibrutinib is not established; the response to subsequent salvage treatment is poor, and survival is short.7 The availability of B cell receptor signaling inhibitors has made the decision of whether to proceed with allo-SCT in high-risk patients more complex; there is no consensus regarding which patients with del(17p) should proceed to allo-SCT or regarding the optimal timing of allo-SCT.
Del(17p) CLL is frequently associated with CKT, which is defined as 3 or more distinct chromosomal abnormalities present in more than 1 metaphase.8 CKT has been associated with inferior outcomes for both treatment-naive patients9, 10 and R/R CLL patients undergoing therapy,11 including allo-SCT12; the prognostic significance of CKT in ibrutinib-treated patients is unknown. Obtaining metaphases for cytogenetic analysis has traditionally been challenging in CLL because of the low ex vivo mitotic rate of CLL cells. Frequently, no abnormalities are detected because only normal hematopoietic cells divide ex vivo or only poor-quality metaphases are obtained.10, 13 Array comparative genomic hybridization (CGH) or FISH does not require cell division14 and may detect abnormalities when no abnormal metaphases are obtained by conventional techniques. However, they provide limited information; array CGH detects genomic imbalances only and provides no information about balanced translocations or the mechanism of gain or loss; FISH provides information only about chromosomes specifically targeted by the probes used.8 Mitogens such as combined immunostimulatory CpG oligonucleotides and interleukin 2 can be used to stimulate ex vivo growth of CLL cells; this substantially increases the yield of analyzable metaphases and increases the proportion of cases in which cytogenetic abnormities are detected by conventional cytogenetic analysis to >80%.15 More than 20% of patients analyzed in this way will have CKT, whereas <1% will be detected by FISH alone.15
We analyzed long-term follow-up data for 88 patients with R/R CLL treated with ibrutinib-based regimens to determine whether subgroups of patients with del(17p) with differing outcomes could be identified and to assess possible novel predictors of outcomes with a particular focus on the prognostic significance of CKT.
PATIENTS AND METHODS
We reviewed 88 patients treated for R/R CLL at The University of Texas MD Anderson Cancer Center with investigational ibrutinib-based regimens from 2010 to 2013. We were interested in patients with long-term follow-up; therefore, only patients who had commenced treatment before June 2013 were included. Thirty-eight patients received ibrutinib monotherapy at either 420 or 840 mg/d, 36 received ibrutinib plus rituximab, and 14 received ibrutinib plus bendamustine and rituximab. Details of the combination regimens were presented previously.16, 17 All patients provided informed consent, and all studies were institutional review board–approved and were conducted according to the Declaration of Helsinki. Pretreatment FISH and lipopolysaccharide-stimulated metaphase cytogenetic analysis18 were performed on bone marrow, although the latter was not required per protocol. Material was considered adequate for karyotypic analysis if 10 or more metaphases were available in the presence of clonal abnormalities or 15 or more were available in the absence of clonal abnormalities.10 Clonal cytogenetic abnormalities were considered to be present when at least 2 or more metaphases showed identical chromosome gain or structural abnormalities or at least 3 metaphases showed identical chromosome loss.19
Statistical analyses were performed with SPSS 22 (IBM Corp, Armonk, NY) and GraphPad Prism 6 (GraphPad Software, La Jolla, Calif). Descriptive statistics were used to summarize patient characteristics. Dichotomous variables were compared with the chi-square test or Fisher's exact test. Univariate survival analyses were performed with the Kaplan-Meier method,20 and differences between groups were assessed with the log-rank test.21 Multivariate analysis (MVA) for dichotomous variables was performed with logistic regression. Multivariate survival analysis was performed with a Cox proportional hazards model.22 Variables with P values < .1 in univariate analyses were included in the multivariate models, and only cases with complete data for variables of interest were included in the multivariate models. Event-free survival (EFS) was defined as the time from the initiation of the study drug to permanent cessation of the study drug for any reason. Overall survival (OS) was defined as the time from the initiation of the study drug to death. Patients were censored at their last follow-up for EFS and survival outcomes. The final censoring date was July 14, 2014. EFS was chosen as an outcome measure rather than PFS to capture potentially significant events that may be associated with the presence of CKT, including the development of second cancers requiring systemic therapy and the decision to proceed to allo-SCT. Seven patients who underwent allo-SCT during partial remission or complete remission (CR) were censored for EFS analysis at the time of transplantation, but they continued to be followed for survival.
RESULTS
Baseline patient characteristics are shown in Table 1.
| Characteristic | Value |
|---|---|
| Age, median (range), y | 66 (35-83) |
| No. of prior therapies, median (range) | 2 (1-12) |
| Male sex, No. (%) | 67 (76) |
| Rai stage, No. (%) | |
| 0-II | 36 (41) |
| III-IV | 52 (59) |
| Bulky adenopathy ≥ 5 cm | 45 (51) |
| FISH hierarchy (n = 86), No. (%) | |
| Del(13q) | 13 (15) |
| No abnormalities | 10 (12) |
| Trisomy 12 | 1 (1) |
| Del(11q) | 28 (33) |
| Del(17p) | 34 (40) |
| Complex metaphase karyotype (n = 56), No. (%) | 21 (38) |
| IGHV mutation status, No. (%) | |
| Unmutated | 72 (82) |
| Mutated | 7 (8) |
| No PCR product obtained | 9 (10) |
| Fludarabine-refractory, No. (%) | 17 (19) |
| β2-microglobulin (n = 75), No. (%) | |
| ≥4.0 mg/l | 43 (57) |
| <4.0 mg/l | 32 (43) |
| Treatment regimen, No. (%) | |
| Ibrutinib monotherapy | 38 (43) |
| Ibrutinib + rituximab | 36 (41) |
| Ibrutinib + BR | 14 (16) |
- Abbreviations: BR, bendamustine and rituximab; FISH, fluorescence in situ hybridization; IGHV, immunoglobulin heavy-chain variable gene; PCR, polymerase chain reaction.
Relation Between Metaphase Karyotype Analysis and Del(17p) by FISH
Metaphase karyotype analysis was attempted for 63 patients, and metaphases were adequate for analysis in 56. The 7 cases for which metaphase analysis was attempted but inadequate data were available had poor-quality metaphases or fewer than 10 metaphases generated. The relationship between FISH and metaphase karyotype results is shown in Figure 1. Among 21 patients with CKT, 17 had del(17p) (odds ratio [OR] vs non-del(17p) patients, 22.7 [95% CI 5.2-99.6]; P < .001), 3 had del(11q), and 1 did not have FISH results available. There was no difference in the percentage of cells with a TP53 deletion by FISH according to the presence or absence of CKT (median, 65% [95% CI 7.5%-86.0%] vs 37% [95% CI 12.0%-96.5%]; P = .32). The 7 patients with TP53 deletion by FISH but without CKT predominantly had a diploid karyotype (n = 6), whereas 1 had add(17p).
Associations between del(17p) by FISH and metaphase karyotype results. FISH indicates fluorescence in situ hybridization.
There were 9 patients who had del(17p) detected by FISH but no abnormalities involving chromosome 17p noted by a concurrent metaphase cytogenetic evaluation. The median percentage of TP53 deletion by FISH in these patients was 30%; the range was 7.5% to 82%. Six of these 9 patients had diploid cytogenetics or noncomplex clonal abnormalities according to the metaphase cytogenetic analysis. Two of these 6 cases had a very low percentage of TP53 deletion by FISH (7.5% and 12%), whereas the remaining 4 cases had ≥24% TP53 deletion by FISH; 1 of these patients had a single metaphase with complex cytogenetic abnormalities, including monosomy 17, and thus did not meet criteria for clonality, but the patient had 37% TP53 deletion by FISH. Three patients had a complex karyotype and del(17p) detected by FISH but no abnormalities involving 17p on conventional cytogenetics; 2 had a low percentage of TP53 deletion by FISH (7.5% and 24%), whereas 1 had 83% TP53 deletion by FISH.
Response to Treatment
The overall response rate for the entire population was 94.3%; 18% achieved CR. The overall response rate did not differ according to baseline characteristics (Table 2). The CR rate was 50% among patients who received ibrutinib plus bendamustine and rituximab versus 10.7% for patients who received ibrutinib monotherapy or ibrutinib plus rituximab (OR, 40.1 [95% CI 3.0-538.5]; P = .005).
| Characteristic | Overall Response, No. (%) | P | Complete Remission, No. (%) | P |
|---|---|---|---|---|
| Total cohort (n = 88) | 83 (94.3) | 16 (18) | ||
| Age | ||||
| ≤65 y (n = 46) | 45 (97.8) | 6 (13.0) | ||
| >65 y (n = 42) | 38 (90.5) | .137 | 9 (21.4) | .296 |
| Sex | ||||
| Male (n = 67) | 63 (94.0) | 15 (22.4) | ||
| Female (n = 21) | 20 (95.2) | .835 | 0 (0) | .017 |
| Treatment regimen | ||||
| Ibrutinib monotherapy (n = 38) | 35 (92.1) | 5 (13.2) | ||
| Ibrutinib + rituximab (n = 36) | 34 (94.4) | 3 (8.3) | ||
| Ibrutinib +BR (n = 14) | 14 (100) | .551 | 7 (50.0) | .001 |
| FISH hierarchy | ||||
| Other (n = 24) | 24 (100) | 8 (33.3) | ||
| Del(11q) (n = 28) | 27 (96.4) | 2 (7.1) | ||
| Del(17p) (n = 34) | 32 (94.1) | .904 | 5 (14.7) | .040 |
| IGHV mutation status | ||||
| Mutated (n = 9) | 7 (77.8) | 4 (44.4) | ||
| Unmutated (n = 72) | 67 (93.1) | .471 | 9 (12.5) | .012 |
| Complex karyotype | ||||
| Yes (n = 21) | 19 (90.5) | 2 (9.5) | ||
| No (n = 35) | 34 (97.1) | .283 | 6 (17.1) | .430 |
| Number of prior therapies | ||||
| <2 (n = 48) | 45 (93.8) | 10 (20.8) | ||
| ≥2 (n = 40) | 38 (95.0) | .801 | 5 (12.5) | .301 |
| Fludarabine-refractory | ||||
| Yes (n = 17) | 15 (88.2) | 1 (5.9) | ||
| No (n = 71) | 68 (95.8) | .228 | 14 (19.7) | .173 |
| β2-Microglobulin | ||||
| ≥4.0 mg/l (n = 43) | 43 (93.0) | 4 (9.3) | ||
| <4.0 mg/l (n = 32) | 32 (100) | .127 | 8 (25.0) | .067 |
| Rai stage | ||||
| 0-II (n = 36) | 35 (97.2) | 9 (25.0) | ||
| III-IV (n = 52) | 48 (92.3) | .328 | 6 (11.5) | .099 |
| Bulky adenopathy (≥5 cm) | ||||
| Yes (n = 45) | 41 (91.1) | 5 (11.1) | ||
| No (n = 43) | 42 (97.7) | .184 | 10 (23.3) | .130 |
- Abbreviations: BR, bendamustine and rituximab; FISH, fluorescence in situ hybridization; IGHV, immunoglobulin heavy-chain variable gene.
In MVA, receiving a bendamustine-containing regimen was strongly associated with the odds of achieving CR (OR, 85.2 [95% CI 3.2-2247.7]; P = .008). Patients with an unmutated immunoglobulin heavy-chain variable (IGHV) gene (OR, 0.001 [95% CI 0.000-0.273]; P = .014) had lower odds of achieving CR, whereas patients with a baseline β2-microglobulin level ≥ 4.0 mg/l (OR, 0.05 [95% CI 0.002-1.13]; P = .051) showed a trend toward lower odds of achieving CR. There was no association between high-risk FISH, sex, or advanced Rai stage and the odds of achieving CR in MVA.
EFS
The median follow-up for surviving patients was 28 months (range, 14-48 months). In univariate analyses, the following were significantly associated with shorter EFS: female sex (median EFS, 22 months vs not reached [NR]; P = .001), advanced Rai stage disease (median EFS, 38.3 months for Rai stages III and IV vs NR for Rai stages 0-II; P = .047), del(17p) (32 months vs NR, P = .021), and CKT (19 vs 39 months, P < .001; Fig. 2). There was a strong trend toward inferior EFS for patients with fludarabine-refractory disease (median EFS, 27 months vs NR; P = .059). There was no association between EFS and a proportion of cells with del(17p) ≥ 50% by FISH, an age > 65 years, the mutation status, bulky lymphadenopathy ≥ 5 cm, a baseline β2-microglobulin level ≥ 4.0 mg/L, or more than 2 prior therapies. In MVA, only CKT was significantly associated with EFS (hazard ratio [HR], 6.6 [1.7-25.6]; P = .006). There was no association between del(17p) by FISH and EFS in MVA (P = .995). When only patients with del(17p) were analyzed, there was a strong trend (P = .056) toward inferior EFS for those with a complex karyotype versus those without one (Fig. 2). We separately analyzed all patients for whom karyotyping was attempted and divided them into 3 groups: those with a diploid karyotype or insufficient metaphases for analysis, those with a complex karyotype, and those with noncomplex clonal abnormalities. Those with a complex karyotype had inferior EFS (P < .0001). There was no significant difference in EFS between patients with a diploid karyotype/insufficient metaphases and those with noncomplex clonal abnormalities (Fig. 2).
EFS analysis. (A) EFS according to FISH hierarchy for all patients. (B) EFS according to the presence or absence of a complex metaphase karyotype. (C) EFS for patients without a complex karyotype according to FISH. (D) EFS for patients with del(17p) according to the coexistence or absence of a complex karyotype. (E) EFS for all patients according to the presence or absence of fludarabine-refractory disease. (F) EFS according to the karyotype group for all patients for whom a karyotype was attempted. EFS indicates event-free survival; FISH, fluorescence in situ hybridization
Events During Treatment and Timing of Events
Events and the timing of events leading to permanent treatment cessation are shown in Table 3. Treatment was very well tolerated, with permanent treatment cessation due to toxicity occurring in only 3 patients; all events occurred before 12 months of therapy (persistent diarrhea in 1, gastrointestinal bleeding in the setting of acquired von Willebrand's disease in 1, and recurrent infections in 1). Nine patients developed progressive CLL, and 5 developed Richter transformation. Notably, all cases of progressive CLL developed beyond 6 months of therapy, and 7 of the 9 cases occurred beyond 12 months of therapy. The 5 cases of Richter transformation occurred 2, 4.5, 13, 21, and 21.5 months after the initiation of therapy. The patient who experienced transformation at 4.5 months had complex chromosomal abnormalities on metaphase analysis but fewer than 10 metaphases available for analysis and was, therefore, included in the unknown karyotype group. Of the 35 patients without CKT, only 1 developed disease progression, and 1 developed Richter transformation, whereas none required therapy for other cancers; none of the 7 patients with del(17p) who did not also have CKT developed disease progression or other cancers, with the only 2 events in these 7 patients being cessation of treatment after 4 months due to gastrointestinal bleeding and death during CR from CLL at 32 months due to staphylococcal pneumonia. In contrast, 4 cases of CLL progression, 3 of Richter transformation, and 3 of other cancers requiring therapy were seen in the 21 patients with CKT. Seven patients underwent planned allo-SCT during remission and were censored for EFS analysis on the date that ibrutinib was last taken.
| Event | Complex Karyotype (n = 21) | No Complex Karyotype (n = 35) | Karyotype Unknown (n = 32) | Total | <12 mo of Therapy | ≥12 mo of Therapy |
|---|---|---|---|---|---|---|
| Death in remission | 4 | 3 | 1 | 8 | 4 | 4 |
| Progressive disease | 4 | 1 | 4 | 9 | 2 | 7 |
| Richter transformation | 3 | 1 | 1 | 5 | 2 | 3 |
| Toxicity | 0 | 1 | 2 | 3 | 3 | 0 |
| Other cancer requiring therapya | 3 | 0 | 0 | 3 | 0 | 3 |
| Allogeneic stem cell transplantb | 3 | 2 | 2 | 7 | 5 | 2 |
| Total events | 17 | 8 | 10 | 35 | 16 | 19 |
- a Ovarian cancer in 2 patients and acute myeloid leukemia in 1 patient.
- b Patients undergoing planned allogeneic stem cell transplantation were censored for the event-free survival analysis at the last ibrutinib dose.
OS
The following were significantly associated with shorter OS in the univariate analysis: fludarabine-refractory CLL (28 months vs NR, P = .009), del(17p) (33 months vs NR, P = .012), and CKT (25 months vs NR, P = .007; Fig. 3). There was a trend for shorter survival in patients with a baseline β2-microglobulin level ≥ 4.0 mg/l (42 months vs NR, P = .078). There was no association between OS and the percentage of cells with del(17p) by FISH, an age > 65 years, sex, an advanced Rai stage, bulky lymphadenopathy ≥ 5 cm, the IGHV mutation status, or more than 2 prior therapies. In MVA, fludarabine-refractory CLL (HR, 6.9 [95% CI 1.8-27.1], P = .005) and CKT (HR, 5.9 [95% CI 1.6-22.2], P = .008) were significantly and independently associated with shorter survival. There was no association between del(17p) and OS (P = .885) in MVA. A separate analysis showed that patients with a complex karyotype had survival inferior (P = .02) to that of patients with noncomplex clonal abnormalities or either a diploid karyotype or insufficient metaphases for analysis. There was no significant difference in survival between patients with a diploid karyotype or insufficient metaphases for analysis and those with noncomplex clonal abnormalities (Fig. 3).
OS analysis. (A) OS according to FISH for all patients. (B) OS according to the presence or absence of a complex metaphase karyotype. (C) OS according to the FISH hierarchy for patients without a complex metaphase karyotype. (D) OS for patients with del(17p) according to the coexistence or absence of a complex karyotype. (E) OS according to the presence or absence of fludarabine-refractory disease. (F) OS according to the karyotype group for all patients for whom a karyotype was attempted. FISH indicates fluorescence in situ hybridization; OS, overall survival.
DISCUSSION
Ibrutinib represents a major advance in the treatment of patients with CLL and particularly those with high-risk R/R CLL. Patients with del(17p) have PFS inferior to that of patients without del(17p),4 but other baseline factors predictive of outcomes have not been established. This retrospective analysis demonstrated that the presence of CKT at study entry was associated with inferior EFS and OS in R/R patients with CLL treated with ibrutinib-based regimens; the outcomes of patients with CKT were poor, with a median survival of only 25 months. In contrast, there was no association between del(17p) and EFS or OS in MVA. The association between del(17p) and inferior PFS in patients treated with ibrutinib may, therefore, in large part be due to the coexistence of CKT rather than the presence of del(17p) per se. Patients without CKT, including the subgroup of patients with del(17p), appeared to have excellent disease-specific outcomes with ibrutinib-based therapy, with a very low rate of CLL progression or Richter transformation; patients with del(17p) but without CKT had relatively good outcomes and appeared to have a low risk of disease progression, although small numbers limit conclusions for this subpopulation. In addition, we identified fludarabine-refractory disease as being associated with inferior OS in MVA.
Technical challenges associated with metaphase cytogenetic analysis have limited its widespread utilization in CLL. During the period of enrollment for the studies we report here, we used lipopolysaccharide stimulation for the culturing of bone marrow specimens, which reportedly achieves rates of analyzable metaphases of approximately 50%.10, 23 The rate of successful metaphase generation was higher in our patient population (56 of 63 patients); this higher rate of metaphase generation may in part be explained by the R/R population, which may have more proliferative CLL clones than untreated populations. There were discrepancies between FISH and metaphase karyotyping in several cases. Notably, 9 of 24 patients with del(17p) detected by FISH had no clonal abnormalities involving 17p detected by the metaphase karyotype. In 2 of 9 cases, the percentage of TP53 deletion by FISH was low, and this likely represented a subclonal population; metaphase analysis may by chance have not detected the 17p deletion because of its low frequency. In the remaining cases, which had ≥24% TP53 deletion by FISH, mitoses may have been obtained from nonneoplastic normal cells rather than the CLL population. These discrepant results illustrate the technical difficulties involved in conventional cytogenetic analysis in CLL, and despite the important information provided by conventional karyotyping, FISH, therefore, remains an essential component of the pretreatment evaluation. It is possible that because of the relative insensitivity of our karyotyping technique, successful metaphase generation is more likely in cases with aggressive CLL clones. To determine whether the ability to generate sufficient CLL metaphases for analysis was strongly associated with outcome, we divided all patients for whom karyotyping was attempted into 3 groups: those with CKT, those with noncomplex clonal abnormalities, and those with either a diploid karyotype or insufficient clonal metaphases for analysis. Importantly, there was no difference in EFS or survival between patients with noncomplex clonal abnormalities and those with either a diploid karyotype or insufficient clonal abnormalities (a significant number of which likely represented a technical failure to generate CLL metaphases for analysis). Recent technical advances, such as the use of CpG oligonucleotides and interleukin 2, pokeweed mitogen, and phorbol myristate acetate, allow the generation of sufficient metaphases for analysis in at least 80% of patients and may limit the number of patients misclassified as a result of technical failure.8, 23 Our laboratory recently started using this combination for conventional karyotyping in CLL. We plan to repeat this analysis with this newer karyotyping technique in a currently enrolling randomized study of 200 patients receiving ibrutinib with or without rituximab.
The precise mechanisms by which del(17p) and CKT contribute to the development of ibrutinib resistance are not clear. These patients may have a higher likelihood of developing specific resistance mutations such as the C481S mutation in BTK and activating mutations in phospholipase Cγ2 because of genomic instability.6 However, these mutations represent only a subset of cases with clinical drug resistance, and additional gene mutations present at the baseline or evolving during therapy may also be important; we did not have gene sequencing data available for patients treated in these studies. Elucidating other causes of ibrutinib resistance to allow subsequent treatment to be rationally selected according to the specific resistance pattern in an individual remains a major research priority.
Important questions remain unanswered regarding the optimal management of high-risk patients, such as those with CKT, initially treated with ibrutinib-based regimens. In contrast to allo-SCT, which achieves long-term remission in approximately 50% of patients with conventionally defined high-risk CLL,2, 24, 25 long-term survival outcomes for high-risk patients treated with ibrutinib-based therapy are unknown; a median OS of only 25 months with ibrutinib-based treatment for patients with CKT, however, clearly indicates a high-risk disease requiring the development of more potent therapy. One potential strategy could be to perform allo-SCT in high-risk patients after ibrutinib-based induction. However, although allo-SCT has been shown to overcome the poor prognosis associated with del(17p),2, 3 only 1 study specifically addressed the outcomes of patients with CKT treated with allo-SCT,12 and it suggested that patients with CKT had poorer outcomes after allo-SCT than those without CKT. This study was small (n = 51), and the majority of patients received in vivo T-cell depletion; in vivo T-cell depletion with alemtuzumab as part of reduced-intensity conditioning for allo-SCT for CLL has been associated with a higher relapse rate and poorer survival outcomes.2 Larger studies are required to address the important question of whether allo-SCT ameliorates the poor outcomes associated with CKT. The outcomes of patients treated with allo-SCT after induction with B cell receptor signaling inhibitors or BCL2 inhibitors such as ABT199 (Venetoclax) are also unknown, as is the optimal timing of allo-SCT in patients responding to ibrutinib. The value of posttransplant maintenance treatment with novel agents will also be important to address in future studies. Finally, the potential for combinations of ibrutinib with other novel agents, particularly BCL2 inhibitors, to induce deeper and more durable remissions and whether this will, in turn, obviate allo-SCT in these high-risk patients need to be assessed.
In summary, CKT may be associated with a particularly poor outcome for R/R CLL patients treated with ibrutinib-based regimens; in contrast, patients with del(17p) in the absence of CKT may have relatively favorable outcomes and require a less aggressive approach. These findings, however, require confirmation in larger groups of patients with more sensitive karyotyping techniques. Because of their poor outcomes, patients with CKT are likely an ideal group for future studies of novel ibrutinib-based combinations or sequential therapies, including allo-SCT.
FUNDING SUPPORT
No specific funding was disclosed.
CONFLICT OF INTEREST DISCLOSURES
Philip A. Thompson receives funding from the CLL Global Research Foundation; he has also received a Haematology Society of Australia and New Zealand New Investigator Scholarship. Susan M. O'Brien, Nitin Jain, and Jan A. Burger have received research funding from Pharmacyclics; Susan M. O'Brien has also received funding from Gilead. William G. Wierda has served as an advisor/consultant for Sanofi, Genentech/Roche, Pharmacyclics, Celgene, Gilead, GlaxoSmithKline/Novartis, Genzyme, Merck, AbbVie, and Emergent; he has been contracted for research for GlaxoSmithKline/Novartis, AbbVie, Genentech, Karyopharm, Pharmacyclics, Ascerta, Gilead, Jansen, Emergent, Juno Therapeutics, and KITE Pharma.
