Treatment of chronic lymphocytic leukemia has greatly advanced in the past few years since introduction of the fludarabine/cyclosphosphamide/rituximab regimen as first-line therapy. Nevertheless, 17p deletion represents a challenge because conventional treatment does not provide satisfactory results. 17p deletion and TP53 mutation are the major factors accounting for rapid disease progression, poor response to therapy, early relapse, and short survival. Allogeneic stem cell transplantation harbors curative potential but also considerable morbidity and mortality. Novel agents acting independently of the p53 signaling pathway, with favorable side-effect profiles, are promising. This review summarizes up-to-date knowledge about 17p deletion and the spectrum of treatment options.
Key points
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As there are also indolent clinical courses in the group of patients with 17p, criteria for treatment initiation should follow the recommendations of the International Workshop on Chronic Lymphocytic Leukemia.
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Physically fit patients with 17p-deleted CLL derive limited benefit from the current standard regimen for first-line therapy fludarabine/cyclophosphamide/rituximab.
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The most promising novel agents with a favorable risk profile, acting independently of the p53 signaling pathway are immunomodulatory drugs, PI3K inhibitors, BH3 mimetics and BTK inhibitors.
Introduction
The introduction of fluorescence in situ hybridization (FISH) of interphase nuclei in the routine diagnostics of chronic lymphocytic leukemia (CLL) has greatly advanced the evaluation of genetic abnormalities. Interphase FISH also allows the detection of genetic abnormalities in nondividing cells. By FISH, genomic aberrations are detected in approximately 80% of CLL cases with a disease-specific probe set. If more than just 1 chromosomal aberration is detected, according to the hierarchical model of Döhner and colleagues, the prognosis is determined by the most unfavorable alteration. Deletions of the short arm of chromosome 17 (17p deletion) are found in 3% to 10% of CLL cases at diagnosis and/or with first-line treatment indication and in 30% to 50% of relapsed/refractory CLL.
Breakpoints are distributed over the 17p10-p11.2 region. TP53 is located in band 17p13.1, is always affected, and is the centerpiece of pathogenic importance of 17p deletions; 80% to 90% of cases with monoallelic 17p deletion harbor TP53 mutation on the remaining allele. TP53 mutation occurs in 8% to 15% of patients at first-line treatment and up to 35% to 50% of cases in refractory CLL.
Introduction
The introduction of fluorescence in situ hybridization (FISH) of interphase nuclei in the routine diagnostics of chronic lymphocytic leukemia (CLL) has greatly advanced the evaluation of genetic abnormalities. Interphase FISH also allows the detection of genetic abnormalities in nondividing cells. By FISH, genomic aberrations are detected in approximately 80% of CLL cases with a disease-specific probe set. If more than just 1 chromosomal aberration is detected, according to the hierarchical model of Döhner and colleagues, the prognosis is determined by the most unfavorable alteration. Deletions of the short arm of chromosome 17 (17p deletion) are found in 3% to 10% of CLL cases at diagnosis and/or with first-line treatment indication and in 30% to 50% of relapsed/refractory CLL.
Breakpoints are distributed over the 17p10-p11.2 region. TP53 is located in band 17p13.1, is always affected, and is the centerpiece of pathogenic importance of 17p deletions; 80% to 90% of cases with monoallelic 17p deletion harbor TP53 mutation on the remaining allele. TP53 mutation occurs in 8% to 15% of patients at first-line treatment and up to 35% to 50% of cases in refractory CLL.
Risk stratification
Genomic abnormalities identify subgroups of CLL patients with different time to progression and survival. It is widely acknowledged that patients with 17p deletion and/or TP53 mutation belong to the ultra–high-risk group. In a multivariate analysis of 100 patients with B-cell CLL, B-prolymphocytic leukemia, or Waldenström macroglobulinemia, TP53 mutation was the strongest prognostic factor for survival and predicted nonresponse to purine analogs, such as fludarabine and pentostatin. Another study of 53 patients with B-cell CLL had reported an association of TP53 gene mutations with poor clinical outcome and drug resistance. In a prospective study of 560 untreated patients, samples were analyzed by conventional cytogenetics. Abnormalities of chromosome 17 were correlated to poor prognosis and observed as the only cytogenetic finding with independent prognostic value in multivariate analysis. In a cohort of 325 patients with CLL analyzed by FISH, 17p deletions were found in 7%. In the multivariate analysis, 17p deletion was identified as a significant prognostic factor: patients with 17p deletion had the worst prognosis.
Nevertheless, there seem to be prognostic differences in the 17p-deleted subgroup itself. There is evidence that acquired 17p deletion by clonal evolution harbors a poor prognosis. A retrospective study of 99 CLL patients with 17p deletion at diagnosis showed clinical heterogeneity; some patients had an indolent clinical course. No progression within 18 months was a favorable sign for long-term stable disease. Risk factors for poor survival in this study were Rai stage 1 or higher, an unmutated immunoglobulin heavy chain variable (IGHV) status, and a 17p deletion in more than 25% of nuclei. Another study described a small subset of patients with loss of TP53 and stable disease at a median follow-up of 64 months. All patients with an indolent clinical course had mutated IGHV status.
The cutoff values for determining 17p deletion by FISH vary (usually 3%–12%) and have to be established in every laboratory by hybridization of normal controls. In one study, initially a level of 20% of 17p-deleted cells was defined as a critical threshold ; however, this 20% threshold seems to have resulted from technical artifact. Based on the same patient cohort, the cutoff was later revised and set to 10%.
The clone with a 17p deletion might be suppressed by effective therapy: 15 patients with 17p deletion at diagnosis and response to therapy (nodular partial remission [PR] or complete remission [CR]) had no evidence for 17p deletion at the time of response. At the time of disease relapse or progression, however, the vast majority of patients again had 17p deletions.
Therapeutic approach
17p deletion and TP53 mutation are prognostic markers for nonresponse to conventional chemotherapy. Thus, alternative therapeutic approaches are needed, which act independently of the p53 signaling pathway ( Fig. 1 ). As discussed previously, there are also indolent clinical courses in the group of patients with 17p deletion and, therefore, criteria for treatment initiation should be obeyed as set forth in the recommendations of the International Workshop on Chronic Lymphocytic Leukemia. Outside clinical trials, treatment approaches for patients with 17p deletion and/or TP53 mutation are chemoimmunotherapy, such as fludarabine, cyclophosphamide, and rituximab (FCR); alemtuzumab; and allogeneic stem cell transplantation. Novel treatment strategies, like targeted therapies, can be offered in clinical trials.
Fludarabine/Cyclophosphamide/Rituximab
Chemoimmunotherapy with FCR is today the standard of care in treatment-naive physically fit CLL patients. In the CLL8 trial, 17p deletions were found in 10% (29/306) of patients in the fludarabine and cyclophosphamide (FC) arm versus 7% (22/315) of patients in the FCR arm. A significant improvement in overall response rate (ORR) and progression-free survival (PFS) was demonstrated for FCR versus FC treatment ( Fig. 2 ). This was not the case for CR and 3-year overall survival (OS) (see Fig. 2 , Table 1 ).
| FC | FCR | P Value | |
|---|---|---|---|
| 17p Deletion | 29/306 (10%) | 22/315 (7%) | |
| CR | 0/29 (0%) | 1/22 (5%) | 0.43 |
| ORR | 10/29 (34%) | 15/22 (68%) | 0.025 |
| PFS at 3 y | 0 | 18% | 0.019 |
| OS at 3 y | 37% | 38% | 0.25 |
These experiences with the FCR combination show that physically fit patients with 17p-deleted CLL may derive some benefit from the current standard regimen for first-line therapy.
Alemtuzumab
The CD52 antibody, alemtuzumab, has been approved for the treatment of fludarabine-refractory CLL in the United States and European Union since 2001 and, since 2007/2008, for first-line treatment of CLL patients. In this context, it has generally been used primarily for those who are not expected to respond to fludarabine, primarily patients with 17p deletion and/or TP53 mutation. The producing company, however, has recently withdrawn the drug from the market.
Alemtuzumab has proved its efficacy, especially in high-risk CLL patients. One randomized trial investigated efficacy and safety of intravenous alemtuzumab compared with chlorambucil in CLL first-line treatment ; 297 patients were included. Alemtuzumab was significantly superior regarding the ORR (83% vs 55%, P <.0001) and rate of complete remissions (24% vs 2%, P <.0001). Alemtuzumab was able to eliminate minimal residual disease in 11 of 36 complete responders.
Another important trial on alemtuzumab evaluated efficacy, safety, and clinical benefit of alemtuzumab in 93 fludarabine-refractory CLL patients who had been exposed to alkylating agents. The ORR was 33% with 2% CR and 31% PR; the median OS was 16 months. There was no information about cytogenetics. The CLL2H trial of the German CLL Study Group (GCLLSG) showed that subcutaneous administration of alemtuzumab in the refractory situation is equally effective as intravenous administration and harbors less adverse effects. A comparatively high number of patients had a 17p deletion (31/103; 30%). Between the different cytogenetic subgroups there were no significant differences in ORR, OS ( Fig. 3 ), PFS, or time to treatment failure. This finding confirms the efficacy of alemtuzumab independent of the p53 signaling pathway.
The combination of alemtuzumab with dexamethasone followed by alemtuzumab maintenance therapy or allogeneic stem cell transplantation in ultra–high-risk CLL (17p deletion or fludarabine refractoriness) was investigated in the CLL2O trial of the GCLLSG. The results were updated at the American Society of Hematology annual meeting 2012; 70 of 131 eligible patients had a 17p deletion with either untreated (n = 42) or relapsed (n = 28) disease. The response rates were particularly high in untreated patients (ORR 98%) but also in the relapsed patients (ORR 79%). At a median follow-up time of 21 months, the median PFS was 38 months in first-line treatment and 10.3 months in relapsed patients. The median OS was not reached in the untreated and 21.3 months in the relapsed subgroup. Compared with the results of the FCR arm of the CLL8 trial (see Table 1 ; ORR 68%, PFS 11.3 months), response rates as well as PFS in the untreated subgroup were higher. Another multicenter study in 39 patients with TP53 deletion tested the combination of alemtuzumab with methylprednisolone ; 39 patients (17 untreated, 22 previously treated) with 17p ( TP53 ) deletion were included. The ORR was 85% and the CR rate was 36%. Concerning the previously untreated subgroup, the CR rate was even higher with 65% versus 14% in previously treated patients ( P = .003). Also, PFS was longer in untreated compared with previously treated patients (18.3 vs 6.5 months, P = .010). Grades 3 to 4 infections occurred in 51% of the patients. In summary, the combination of Alemtuzumab with high-dose steroids led to high response rates, but survival was still inferior to the patients without TP53 alterations in the CLL8 trial of the GCLLSG.
Allogeneic Stem Cell Transplantation
According to the European Group for Blood and Marrow Transplantation transplant consensus, indications for allogeneic hematopoietic stem cell transplantation in CLL include patients with p53 abnormalities requiring treatment. In these patients, transplantation should be considered early during the course of the disease.
Several investigations have shown graft-versus-leukemia activity in CLL. A retrospective review of European Group for Blood and Marrow Transplantation data was conducted to assess the curative potential of allogeneic hematopoietic stem cell transplantation in CLL patients with 17p deletion. The course of 44 patients with a median age of 54 years was analyzed. The 3-year OS and PFS rates were 44% and 37%. CR after HCT was ongoing in 9 patients with a follow-up time between 4 and 8.5 years. The CLL3X trial of the GCLLSG investigated the long-term outcome of reduced-intensity conditioning allogeneic stem cell transplantation in CLL patients ; 13 of 72 (18%) patients who proceeded to transplantation harbored a 17p deletion. With a median follow-up of 43 months, 7 of these had still an ongoing complete remission. The 4-year event-free survival and OS rates were 45% and 59%. Neither event-free survival nor OS was significantly different between the various cytogenetic subgroups, implicating that allogeneic stem cell transplantation may overcome the cytogenetic risk profile.
In summary, allogeneic stem cell transplantation should be recommended as a consolidation strategy for patients with 17p deletion requiring therapy with younger age, good performance status, and preferentially a remission after induction therapy as well as few prior therapies.
Flavopiridol
Flavopiridol (alvocidib) is a cyclin-dependent kinase inhibitor, which induces apoptosis in CLL cells, independently of p53, and decreases the expression of antiapoptotic molecules, such as Mcl-1 and XIAP. A prospective study in 64 relapsed CLL patients with 21 (33%) 17p-deleted cases showed no association of 17p deletion with response ( P >.50), which was defined as CR, nodular PR, or PR. Furthermore, there was no significant difference in PFS between present and absent 17p deletion (12.1 vs 10.3 months; P = .94). In a recently published follow-up of 112 patients, the ORRs did not differ between the cytogenetic subgroups ( P = .17). CLL with 17p deletion showed an ORR of 48%. Also, PFS was not different between the subgroups with 10.4 months for 17p-deleted patients. Nevertheless, the risk for progression increased over time for patients with 17p deletion or 11q deletion: at 24 months, just 4% of 17p-deleted patients versus 24% in the group without 17p or 11q deletions were still progression-free. The median OS in 17p-deleted patients was 19.8 months and again not different from other cytogenetic subgroups. The further commercial development of flavopiridol was stopped, however, based on results of a pivotal trial, which showed satisfactory clinical activity in a high-risk subgroup but also considerable toxicity.
Lenalidomide
Lenalidomide is an orally bioavailable immunomodulatory drug derived from thalidomide. Its effects in CLL are mediated by stimulation of natural killer cells and cytotoxic T cells and by influencing the tumor microenvironment. Two adverse events are characteristic: tumor flare and tumor lysis. Two phase II trials showed the efficacy of lenalidomide in relapsed or refractory CLL with ORRs of 47% and 32%, respectively. A separate analysis of cases with high-risk cytogenetics (17p or 11q deletion) was published for the first trial; 6 of 45 patients had a 17p deletion. In this small subgroup, no CR and just one PR were achieved. In the second trial, 8 of 44 (18%) patients had a 17p deletion. Overall response in these patients was 13%. A recent phase I trial identified 20 mg as the maximum tolerated dose in relapsed and refractory CLL. Neutropenia and thrombocytopenia were the most common adverse events. Another phase II trial of lenalidomide combined with rituximab in 59 patients with relapsed and refractory CLL showed an ORR of 66%, with 12% CR and 12% nodular PR; 25% of the patients had a 17p deletion and the ORR in this subgroup was 53%. Moreover, patients with 17p deletion without refractoriness had a similar time to failure as patients with neither 17p deletion nor refractoriness ( Fig. 4 ). Currently, lenalidomide is being further investigated in first-line trials and as maintenance therapy after successful induction treatment (eg, CLLM1 trial of the GCLLSG).
Related posts:
The Significance of Stereotyped B-Cell Receptors in Chronic Lymphocytic Leukemia
The Role of Minimal Residual Disease Measurements in the Therapy for CLL
The Evolving Role of Stem Cell Transplantation in Chronic Lymphocytic Leukemia
Biology of Chronic Lymphocytic Leukemia in Different Microenvironments
The Significance of Stereotyped B-Cell Receptors in Chronic Lymphocytic Leukemia
Chimeric Antigen Receptor Therapy for Chronic Lymphocytic Leukemia
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