Therapy-Related Myeloid Neoplasms in Chronic Lymphocytic Leukemia and Waldenstrom’s Macroglobulinemia

Ricci Francesca, Tedeschi Alessandra, Montillo Marco and Morra Enrica.

¹Division of Hematology, Niguarda Ca’ Granda Hospital, Milano, Italy

Correspondence to: Francesca Ricci, M.D. Division of Hematology, Niguarda Ca’ Granda Hospital. Piazza Ospedale Maggiore 3, 20162 Milano, Italy. Tel. +39-0264442668, Fax: +39-0264442033. e-mail: francesca.ricci@ospedaleniguarda.it

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited

Abstract

Introduction
Advances in the treatment of Chronic Lymphocytic Leukemia (CLL) and Waldenström Macroglobulinemia (WM) have resulted in higher response rates and more durable remissions. Chemoimmunotherapy has become the standard of care and the addition of rituximab to combination chemotherapy is associated with improved outcomes.[1-5] As a result, the number of cancer survivors is rapidly growing and the late toxicities of treatment particularly therapy-related myeloid neoplasms (t-MN) have become a more important concern.
Some authors have reported an increasing incidence of these late complications over the years6 probably due to the better diagnostic criteria employed, increased age of population and  widespread and successful use of drug combination in cancer patients.
A comprehensive review of reported myelodysplasia and acute myeloid leukemia (MDS/AML) rates concluded that up to 10% of patients treated for indolent non-Hodgkin’s lymphoma (NHL) using either conventional dose alkylating agents-based regimens or high-dose therapy develop MDS or AML within a decade of primary therapy.[7] Based on these data the risk of therapy-related MDS/AML is an important consideration in the initial choice of therapy in these conditions.
In this review we have summarized the possible mechanisms of leukemogenesis, analyzed studies conducted to delineate the incidence of secondary MDS/AML in patients with CLL and WM and discussed the potential relationship between these events and treatment with NA and alkylating agents.

Drugs Inducing Secondary Myeloid Neoplasms and Mechanism of Leukemogenesis
Important discoveries have been made over recent years that have contributed to a better understanding of the pathogenesis of  neoplasm and in particular of secondary AML/MDS. There are several lines of evidence showing that different mechanisms cooperate in leukemogenesis defining a  multistep process.
Disease related immunodeficiency, resulting from both cell mediated and humoral-mediated immunity defects, has been postulated as a possible mechanism predisposing to second cancers in non Hodgkin lymphoma (NHL) and in particular in CLL and WM patients. B-cell impairment, low gammaglobulin levels and quantitative and functional defects of various subsets of T cells have all been documented in lymphoprolipherative diseases and are implicated in defective immune surveillance favouring second cancers. In line with this hypothesis is the documented incremented occurrence of malignant tumours in patients having a background of humoral immunodeficiency or abnormalities in T-cell function such as common variable immunodeficiency, ataxia-telangectasia, HIV disease.[8,9] Furthermore, some authors underline the crucial role of the immune system in the oncogenesis reporting an increased risk of second cancers also in untreated CLL and WM patients.[10,11]
However, several studies have raised concerns about the role of therapy in the development of second malignancies and t-MN are a well recognized distinct entity in the 2008 WHO classification of tumors of  hematopoietic and lymphoid tissues.[12]
Cytotoxic agents associated with this complication include alkylating agents, topoisomerase II inhibitors, ionizing radiation, antimetabolites and antitubulin agents.[12,13] The WHO classification considers therapy-related MDS/AML as a unique clinical syndrome even though some cases may satisfy the morphological or cytogenetic criteria for other entities. Indeed, particular cytotoxic agents are associated with therapy-related MDS/AML with characteristic biological and clinical features.
Alkylating agents damage DNA either by methylation or DNA inter-strand crosslink formation. The latency between treatment and t-MN is generally long, between 5 and 7 years and  may be preceded by a myelodysplastic phase. Most cases present deletion or loss of the long arm or total loss of chromosome 5 (5q-/-5) and/or deletion or loss of the long arm or total loss of chromosome 7 (7q-/-7).[14-16]
Topoisomerase II is an essential enzyme in eukaryotic cells and is thought to play an important role in DNA replication, transcription and cell division. This enzyme catalyzes the breaking and rejoining of both DNA strands. Topoisomerase II inhibitors block the enzymatic reaction through relegation and enzyme release, leaving the DNA with a permanent strand break. Multiple DNA-strand breaks lead to cell death.  Both the antineoplastic effect and the leukemogenic effect are due to chromosomal break-age and this breakage, resolved by chromosomal translocation, is the cause of the leukaemic transformation. A shorter latency of approximately 2 years characterized t-MN secondary to  topoisomerase II inhibitors. Balanced chromosome translocations frequently reported after exposure to this chemotherapeutic agents  involve 11q23 (MLL) or 21q22 (RUNX1). However, others may also occur, for example t(8;21) or t(15;17) in the case of therapy-related acute promyelocytic leukemia (t-APL).[12,17,18]
Antimetabolites share structural similarities with nucleotides, and can be incorporated into DNA or RNA, causing inhibition of cell proliferation. Among antimetabolite agents fludarabine is the nucleoside analogs (NA) more frequently used in the treatment of indolent lymphoproliferative disorders.[19] The combination of fludarabine with cyclophosphamide or other DNA damaging agents may increase the risk of MDS/AML due to synergistic effects in the ability to produce DNA damage. Fludarabine inhibits DNA repair and augments the cytotoxic effect of DNA damaging agents such as cyclophosphamide.[20] This enhancement of DNA damage may also affect marrow progenitor cells. Such a mechanism could explain the observed impairment of peripheral blood progenitor cell collection after prior fludarabine treatment and could predispose to an increased risk of therapy-related MDS/AML.[21] High occurrence of abnormalities of chromosome 5 and 7 has also been described  in MDS/AML secondary to NA therapy.[22-24]
In addition to typical genetic abnormalities, t-MN are characterized by molecular changes which may cooperate in the pathogenesis of the disease. FLT3 and p53 mutations are the most frequent described. Chimeric rearrangement of transcription factors, including AML1, CBFB, MLL or RARA and NPM1 mutations have also been reported.[25]
An important role in the multistep secondary
leukemogenesis has been recently attributed to the epigenetic changes. Epigenetic mechanisms such as DNA methylation, post-translational modifications of histone proteins and remodelling of nucleosomes affect chromatin structure and contribute to define heritable changes in gene expression. The abnormalities in DNA methylation profile have been described more commonly in therapy-related rather than de novo MDS/AML.[26]
Since only a small fraction of patients exposed to cytotoxic therapy developed t-MN, one of the important questions in the field is what predisposes individuals to develop the disease. A large number of studies have offered evidence demonstrating the importance of genetic variation in key genes, which include those involved in drug metabolism, protection of cellular entities from damage and repair of DNA damage. Mutations in these vital genes are rare while much more common are genetic polymorphisms in detoxification genes and in genes belonging to the major DNA repair pathways.[18]
Although the multistep leukemogenesis mechanism has not been completely clarified, the important knowledge achieved in the last years in this matter has laid the groundwork to a risk adapted therapeutic approach. An adequate screening of individual susceptibility to develop t-MN could influence initial treatment strategies with the goal of decreasing the incidence of these serious complications.

Waldenstrom Macroglobulinemia
WM patients have a well documented increased risk of second cancers and in particular of secondary MDS/AML. Although disease-related immune-suppression has been suggested as one of the main causes of this increasing risk,10 the role of therapy in this important matter is under investigation.
Several studies have been conducted in Europe and in the United States to retrospectively examine the incidence of secondary MDS/AML in treated WM patients.
Alkylating agents and NA such as fludarabine and 2-chlorodeoxyadenosine (2-CdA) have been considered  appropriate first line agents for the treatment of WM.[27-28]
Among patients receiving alkylating agents the incidence of such events ranged from 0 to 6% (Table 1) in different retrospective studies.[29-33] Among them the most consistent data have been published by Ghobrial et al33 on 337 patients  with newly diagnosed  symptomatic WM. After a median duration of follow  up of 11 years death occurred in 237 (70%) patients. The cause of death was due to WM or complications of therapy in 125 cases (37%) cases. Of these, death due to MDS/AML occurred in 16 patients (4.7%) indicating that this is a serious and fatal complication of alkylating agents therapy.

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Table 1. MDS/AML occurrence in WM patients treated with alkylating agents

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More recently attention has been focused on long term toxicity of NA-based therapy [34,35] and retrospective comparative data has been reported by the French Cooperative Group on CLL/WM36 and by the Dana-Farber Cancer Institute.[37]
Leblond et al36 reviewed the incidence of secondary MDS/AML in 165 WM patients treated with NA agents in 3 trials performed from 1993 to 2003 by the French Cooperative Group on CLL/WM.
In the first trial [38] 71 relapsed/refractory WM patients initially treated with alkylating agents  received fludarabine. In the second trial [32] 92 patients in first relapse after alkylating agents were randomized to receive fludarabine and CAP regimen (doxorubicine, cyclophosphamide, prednisone). In the third trial [39] 49 patients with untreated or pretreated disease received fludarabine combined with cyclophosphamide.
The crude incidence of secondary MDS/AML varied from 1.4 to 8.9% in patients treated with fludarabine alone and was 6% in patients treated with fludarabine combined with cyclophosphamide. Incidence of such events were not different in the two groups of patients. More recently Leleu et al [37] carried out a retrospective study to delineate the incidence of secondary MDS/AML in a large population of patients with WM and to determine the potential relationship between these events and treatment with NA. Among the 439 consecutive patients considered in this study 329 were treated with (193) or without (136) NA and 110 patients remained untreated.  The median follow-up for all patients was 5 years. Overall 3 patients (1.6%) developed secondary MDS/AML among NA treated patients while no events were reported in both patients receiving other chemotherapeutic drugs and in untreated patients  The 15-year probabilities of developing secondary MDS/AML were 8%.  These data demonstrate an increased incidence of developing secondary MDS/AML among patients with WM treated with NA. The incidence of MDS/AML was not statistically different in patients treated with NA as first line treatment versus patients treated later in their disease history, in patients treated with either one or with multiple courses of NA, and in patients with history versus no history of treatment with an oral alkylating agent. Among the three patients who developed MDS/AML in this series, only one patient had previously received oral alkylating agents therapy. Furthermore, none of the clinical and laboratory features studied (gender, age, family history of haematological malignancies, markers of tumor burden, prognosis markers including WM-ISS) significantly predicted  the occurrence of  secondary MDS/AML events. However, no definite conclusion can be drawn because of the low number of events and therefore a lack of power in multivariate analysis might also explain that no risk factors except treatment with NA were observed.
Data reported in all these retrospective studies (Table 2) lead to conclude that although a role of NA in leukemogenesis has been wide recognized other data and prospective studies are needed to clarify  the impact of fludarabine and alkylating agent combination compared to fludarabine alone in the increased risk of  t-MN in WM patients.
In the last decade the use of rituximab has also been extensively evaluated in patients with WM and high activity of fludarabine and rituximab combination with or without cyclophosphamide has been demonstrated.
Treon et al [40] reported the long term outcome of a multicenter prospective study examining fludarabine and rituximab association in 43 WM patients with less than two prior therapies. With a median follow-up of 40.3 months, 3 patients (7%) developed myeloid malignancies: MDS in one case and AML in two cases. Among them one had previously received chlorambucil and another had previously undergone high-dose chemotherapy with an autologous transplantation. The median time from protocol therapy to secondary MDS/AML was 39.4 months. 
More recently toxicities data of fludarabine, cyclophosphamide and rituximab combination (FCR) have been reported by Leblond et al [41] in 55 WM patients. Among them 40  had been previously  treated with a median of 2 lines of therapy (range 1-4), including 24 patients with relapsed disease and 16 patients with refractory disease. After a median follow-up of 28 months secondary MDS/AML were observed in two heavily treated patients (3.6%).  Similar results have been observed by Tedeschi et al in a group of 43 untreated and  pretreated patients receiving FCR schedule: MDS occurred in three patients (6.9%), all of them previously heavily pretreated with alkylating agents, after 5, 24 and 60 months from FCR, respectively.[42] Based on these data, addition of rituximab to fludarabine containing regimens does not seem to increase the incidence of t-MN (Table 2).

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Table 2. MDS/AML occurrence in WM patients treated with fludarabine–based regimens.

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Although data on fludarabine treatment are more consistent,  recent analysis of long term toxicity after 2-CdA therapy has also been  published.
The MD Anderson Cancer Center performed a retrospective analysis of 111 consecutive, previously untreated patients with symptomatic WM who received 2 consecutive 4–6-week courses of either 2-CdA alone or in combination with other agents including prednisone, cyclophosphamide, and rituximab. Thirteen patients (12%) developed second malignancies, among them one patient had AML (0.9%). The median time to development of a second malignancy was 85.5 months.[43]
Laszlo et al [44] recently reported the results with 2CdA and rituximab combination in 29 WM patients in first line therapy or previously treated without NA. With a median follow-up of 43 months no secondary MDS/AML was observed.

Chronic Lymphocytic Leukemia
Second malignancies are frequent complications in patients with CLL. The most frequent event is CLL transformation to large B-cell non-Hodgkin’s lymphoma also known as Richter’s syndrome.[45-47] However, the secondary development of myeloproliferative disorders as well as solid tumors has also been documented in CLL patients.[48,49]
An increased incidence of these late complications has  occasionally been reported in patients receiving alkylating agents. However, occurrence of therapy-related MDS/AML after exposure to alkylating agents seems to be lower when they are used intermittently as opposed to prolonged, continuous exposure.[50]
The study of French Cooperative Group on CLL reported data of two randomized trials in 1535 patients with previously untreated stage A CLL.[50] In the first trial, 609 patients were randomly assigned to receive either daily chlorambucil or no treatment; in the second trial, 926 patients were randomly assigned to receive either intermittent chlorambucil plus prednisone or no treatment. Median follow-up for the first and second trials exceeded 11 and 6 years, respectively. CLL patients receiving either intermittent chlorambucil and prednisone or no treatment showed no increase of second tumors; in particular AML was observed in only one case (0.2%). However, a higher frequency of second cancers was reported in the group of patients treated with daily chlorambucil and AML occurred in 4  cases (1.3%).
No evidence of an increased risk of secondary MDS/AML was reported at M.D Anderson Cancer Center in a retrospective analysis of 1374 consecutive CLL patients, even though nearly three quarters of these patients had received prior treatment with alkylating agents.[51] Authors suggest that the suppressive properties of disease–related cytokines acting on myeloid clones may be responsible for the lack of an increased rate of secondary AML/MDS in CLL despite prolonged treatment with alkylating agents and disease related immunosuppression.
In contrast to the published experience with alkylating agents, secondary MDS/AML are rarely reported following NA as monotherapy in CLL patients.[52-56] However, the combination of NA with alkylating agents or other DNA damaging agents may increase the t-MN risk due to their synergistic effects (Table 3). 

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Table 3. MDS/AML occurrence in CLL patients treated with NA–based regimens.

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Morrison et al. presented data from intergroup CLL treatment trial comparing treatment with chlorambucil, fludarabine or chlorambucil plus fludarabine, in which a possible increase in the number of cases of therapy- related AML was observed.[57] With a median follow-up of 4.2 years, six patients (1.2%) developed therapy-related MDS or MDS evolving to AML, from 27 to 53 months after study entry. This includes five (3.5%) of 142 patients treated with chlorambucil plus fludarabine and one (0.5%) of 188 receiving fludarabine. In the group treated with chlorambucil alone MDS or AML were not observed. These findings may indicate that alkylating agents combined with NA may increase the risk of therapy-related MDS/AML in CLL patients.
These data have been recently confirmed by the prospective randomized phase 3 trial, E2997, comparing FC with F alone as initial therapy in 278 CLL patients. With a median follow-up of 6.4 years, there have been 13 cases of t-MN, 9 cases after FC and 4 after fludarabine alone. The increased incidence of t-MN after FC, usually in the absence  of additional treatment, suggests that FC is more leukemogenic than fludarabine.[58]
In contrast Robak et al.[45] did not observed any MDS or AML in a retrospective series of  1487 CLL patients treated with 2-CdA, alkylating agents or both.
In the last five years chemoimmunotherapy regimens including rituximab showed high activity in CLL patients improving quality and duration of responses.  The chemoimmunotherapy FCR has become a standard treatment for CLL based on the German CLL Study Group (GCLLSG) frontline CLL8 trial and the International REACH trial for patients in first relapse.[1,2]
Data of long term follow-up of FCR-therapy has been published by Badoux et al59 in a group of 284 previously treated patients followed in M. D. Anderson Cancer Center. Among them nine patients (3%) developed secondary MDS or AML (n=1) with a median of 20 months from starting FCR. Eight of these nine patients died after a median OS time of 23 months from FCR therapy. Comparable data has been reported by the same group4 with first-line FCR therapy: after a median follow-up  of 6 years MDS occurred during first remission in 8 of 224 patients (2.8%) receiving immunochemotherapy.
More recently results published by Cancer and Leukemia Group Study60 suggest that incidence of t-MN does not increase with Fludarabine-rituximab combination (FR) without cyclophosphamide. After a median follow-up of  117 months none of untreated patients receiving fludarabine-rituximab concurrent or sequential combination developed t-MN during remission. Only one patient experienced therapy-related MDS, however, this occurred 45 months after FR treatment and 9 months after salvage treatment with FCR combination.
Studies examining consolidative autologous stem cell transplantation in CLL have also reported an increased risk of t-MN. Gribben et al identified in the Dana Farber series,  an actuarial incidence of MDS/AML of 12% at 8 years.[61 ]The 137 patients considered in this series received conditioning regimen with cyclophosphamide and total body irradiation. Previous debulking therapy consisted of alkylating agents and/or fludarabine and/or rituximab. 
A lower incidence of secondary MDS/AML was reported by the German CLL-3 trial with three cases in 150 patients who underwent autograft.[62]
As well as the Dana Farber group a high occurrence of MDS/AML has also been described by  Milligan et al in patients enrolled in the Medical Research Council Chronic Lymphocytic Leukaemia-5 trial.[63] Of 115 newly diagnosed patients treated with fludarabine, 65 patients proceeded to autologous transplant. Conditioning was cyclophosphamide and total body irradiation in 49 (75%) patients and chemotherapy in 12 (18%). Ten patients developed MDS/AML; eight had undergone an autograft. Risk of MDS/AML was not associated with type of prior therapy. Five-year actuarial risk of developing MDS/AML postautograft was 12.4%. No analysed potential risk factor was predictive for MDS/AML development. Authors hypothesise that potential causative factors are fludarabine, low cell dose and transplant conditioning. The UK and German data differ in that there is an increased exposure to fludarabine and a lower infused cell dose in the UK. It has been suggested that the relatively low cell dose infused permitted a preferential expansion of damaged residual host stem cells, and that the myeloablative conditioning treatment will not destroy all hematopoietic cells with proliferative potential.
Recently results published of a phase 3 randomized trial of autografting in CLL versus observation for responding patients after first or second line treatment reported MDS in 4 patients: 3 in the autografiting arm (2.7%) and 1 in the observation arm (0.9%). The relatively low occurrence of MDS in the autotransplantation arm may be related to the limited follow-up of 5 years after randomization.[64]

Conclusions
The increased risk of secondary malignancies occurring in WM and CLL patients is well documented.
Overall published data reported frequently higher occurrence of t-MN in WM rather than in CLL patients, while in CLL patients transformation to Richter’s syndrome or the evolution to prolymphocytic leukemia is the more frequent long term complication.
The complex immunodeficiency resulting from B-cell impairment, hypogammaglobulinemia, T-cell dysfunction and decreased natural killer-cell activity, associated with these diseases may play a crucial role in leukemogenesis. However, there is  great concern that therapy, especially with alkylating agents and purine nucleoside analogs, may further contribute to increase the risk of this devastating complication.
Although in the last few years several retrospective studies have been published on this topic, the real impact on risk of secondary  MDS/AML complication of the single therapeutic agents has not been  definitively clarified.
Indeed assessment of the specific risk is often confounded in patients with indolent lymphoprolipherative diseases by frequent exposure to multiple lines of cytotoxic therapy. Rates of secondary myeloid malignancies also vary with the length of follow-up and  estimation may be falsely high if early reversible dysplastic features and cytopenia associated with cytotoxic treatment are misinterpreted.
Furthermore, the role played by additional immunosuppression due to the introduction of monoclonal antibodies in clinical practice needs to be better understood.     
These considerations lead to conclude that the impact of secondary MDS/AML and the role of old and new drugs in the development of these late complications needs to be better evaluated in larger prospective studies, especially in young patients. In view of these data, we suggest that risk versus benefit should be considered when treating younger WM and CLL patients.

References 

1. Robak T, Moiseev S, Dmoszynska A, Solal-CélignyP, Warzocha K, Loscertales J, Catalano J, Afanasiev BV, Larratt L, Geisler C, Montillo M, Ganly P, Dartigeas C, Rosta A, Janssens A, Mendila M, Maurer J, Wenger MK. Rituximab, Fludarabine, and Cyclophosphamide (R-FC) Prolongs Progression Free Survival in Relapsed or Refractory Chronic Lymphocytic Leukemia (CLL) Compared with FC Alone: Final Results from the International Randomized Phase III REACH Trial. Blood (ASH Annual Meeting Abstracts) 2008; 112: lba-1 
2. Hallek M, Fischer K, Fingerle-Rowson G, Fink AM, Busch R, Mayer J, Hensel M, Hopfinger G, Hess G, von Grünhagen U, Bergmann M, Catalano J, Zinzani PL, Caligaris-Cappio F, Seymour JF, Berrebi A, Jäger U, Cazin B, Trneny M, Westermann A, Wendtner CM, Eichhorst BF, Staib P, Bühler A, Winkler D, Zenz T, Böttcher S, Ritgen M, Mendila M, Kneba M, Döhner H, Stilgenbauer S. International Group of Investigators; German Chronic Lymphocytic Leukaemia Study Group.Addition of rituximab to fludarabine and cyclophosphamide in patients with chronic lymphocytic leukaemia: a randomised, open-label, phase 3 trial. Lancet 2010; 376:1164-74.doi:10.1016/S0140-6736(10)61381-5
3. Dimopoulos MA, Anagnostopoulos A, Kyrtsonis MC, Zervas K, Tsatalas C, Kokkinis G, Repoussis P, Symeonidis A, Delimpasi S, Katodritou E, Vervessou E, Michali E, Pouli A, Gika D, Vassou A, Terpos E, Anagnostopoulos N, Economopoulos T, Pangalis G. Primary treatment of Waldenström macroglobulinemia with dexamethasone, rituximab, and cyclophosphamide. J Clin Oncol. 2007; 25: 3344-9.doi:10.1200/JCO.2007.10.9926 PMid:17577016
4. Tam CS, O'Brien S, Wierda W, Kantarjian H, Wen S, Do KA, Thomas DA, Cortes J, Lerner S, Keating MJ. Long-term results of the fludarabine, cyclophosphamide, and rituximab regimen as initial therapy of chronic lymphocytic leukemia. Blood 2008;112: 975-80. doi:10.1182/blood-2008-02-140582 PMid:18411418
5. Wierda W, O'Brien S, Wen S, Faderl S, Garcia-Manero G, Thomas D, Do KA, Cortes J, Koller C, Beran M, Ferrajoli A, Giles F, Lerner S, Albitar M, Kantarjian H, Keating M. Chemoimmunotherapy with fludarabine, cyclophosphamide, and rituximab for relapsed and refractory chronic lymphocytic leukemia. J Clin Oncol. 2005; 23: 4070-8. doi:10.1200/JCO.2005.12.516 PMid:15767647
6. Leone G, Mele L, Pulsoni A, Equitani F, Pagano L.The incidence of secondary leukemias. Haematologica. 1999; 84:937-45. PMid:10509043
7. Armitage JO, Carbone PP, Connors JM, Levine A, Bennett JM, Kroll S. Treatment-related myelodysplasia and acute leukemia in non-Hodgkin's lymphoma patients. J Clin Oncol. 2003; 21:897-906. doi:10.1200/JCO.2003.07.113 PMid:12610191
8. Dasanu CA, Alexandrescu DT. Risk for second nonlymphoid neoplasms in chronic lymphocytic leukemia. MedGenMed. 2007; 9: 35.
9. Greene, M.H., Hoover, R.N. and Fraumeni, J.F. Subsequent cancer in patients with chronic lymphocytic leucemia a possible immunologic mechanism. J Natl Cancer Inst. 1978; 61: 337-340.PMid:277720
10. Varettoni M, Tedeschi A, Arcaini L, Pascutto C, Vismara E, Orlandi E, Ricci F, Corso A, Greco A, Mangiacavalli S, Lazzarino M, Morra E. Risk of second cancers in Waldenstrom macroglobulinemia. Ann Oncol. 2011; Apr 27;--(--):--Robak T. Second malignancies and Richter's syndrome in patients with chronic lymphocytic leukemia. Hematology. 2004; 9:387-400 doi:10.1080/10245330400018599 PMid:15763979
11. Robak T. Second malignancies and Richter's syndrome in patients with chronic lymphocytic leukemia. Hematology. 2004; 9:387-400. doi:10.1080/10245330400018599 PMid:15763979
12. Vardiman JW, Arber DA, Brunning RD, Larson RA, Matutes E, Baumann I, Thiele J. Swerdlow SH, Campo E, Harris NL, Jaffe ES, Pileri SA, Stein H, Thiele J, Vardiman JW, ed. Therapy-related myeloid neoplasms - WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. Fourth Ed. Lyon, France: IARC Press. 2008; 127-9. 
13. Seymour JF, Juneja SK, Campbell LJ, Ellims PH, Estey EH, Prince HM. Secondary acute myeloid leukemia with inv(16): report of two cases following paclitaxel-containing chemotherapy and review of the role of intensified ara-C therapy. Leukemia. 1999; 13: 1735-40. doi:10.1038/sj.leu.2401552 PMid:10557046
14. Pedersen-Bjergaard J, Pedersen M, Roulston D, Philip P. Different genetic pathways in leukemogenesis for patients presenting with therapy-related myelodysplasia and therapy-related acute myeloid leukemia. Blood. 1995; 86: 3542–52.PMid:7579462
15. Mauritzson N, Albin M, Rylander L, Billstrom R, Ahlgren T, Mikoczy Z, Björk J, Strömberg U, Nilsson PG, Mitelman F, Hagmar L, Johansson B. Pooled analysis of clinical and cytogenetic features in treatment-related and de novo adult myeloid leukaemia and myelodysplastic syndromes based on a consecutive series of 761 patients analyzed 1976-1993 and on 5098 unselected cases reported in the literature 1974-2001. Leukemia. 2002; 12: 2366–78. doi:10.1038/sj.leu.2402713 PMid:12454741
16. Smith SM, Le Beau MM, Huo D, Karrison T, Sobecks RM, Anastasi J, Vardiman JW, Rowley JD, Larson RA. Clinical-cytogenetic associations in 306 patients with therapy-related myelodysplasia and myeloid leukemia: the University of Chicago series. Blood. 2003; 102: 43–52. doi:10.1182/blood-2002-11-3343 PMid:12623843
17. Rowley JD, Olney HJ. International workshop on the relationship of prior therapy to balanced chromosome aberrations in therapy-related myelodysplastic syndromes and acute leukemia: overview report. Genes Chromosomes Cancer 2002; 33:331-45. doi:10.1002/gcc.10040 PMid:11921269
18. Leone G, Fianchi L, Pagano L, Voso MT. Incidence and susceptibility to therapy-related myeloid neoplasms. Chem Biol Interact. 2010; 184:39-45. doi:10.1016/j.cbi.2009.12.013PMid:20026017
19. Keating MJ, O'Brien S, Lerner S, Koller C, Beran M, Robertson LE, Freireich EJ, Estey E, Kantarjian H. Long term follow-up of patients with chronic lymphocytic leukemia (CLL) receiving fludarabine regimens as initial therapy. Blood 1998; 92: 1165-71.PMid:9694704
20. Yamauchi T, Nowak BJ, Keating MJ, Plunkett W. DNA repair initiated in chronic lymphocytic leukemia lymphocytes by 4-hydroperoxycyclophosphamide is inhibited by fludarabine and clofarabine. Clin Cancer Res. 2001; 7: 3580-9. PMid:11705880
21. Morgan SJ, Seymour JF, Grigg A, Matthews JP, Prince HM, Wolf MM, Januszewicz EH. Predictive factors for successful stem cell mobilization in patients with indolent lymphoproliferative disorders previously treated with fludarabine. Leukemia. 2004;18: 1034-8.doi:10.1038/sj.leu.2403326 PMid:14990978
22. Morrison VA, Rai KR, Peterson BL, Kolitz JE, Elias L, Appelbaum FR, Hines JD, Shepherd L, Larson RA, Schiffer CA. Therapy-related myeloid leukemias are observed in patients with chronic lymphocytic leukemia after treatment with fludarabine and chlorambucil: results of an intergroup study, cancer and leukemia group B 9011. J Clin Oncol. 2002; 20: 3878-84.doi:10.1200/JCO.2002.08.128 PMid:12228208
23. McLaughlin P, Estey E, Glassman A, Romaguera J, Samaniego F, Ayala A, Hayes K, Maddox AM, Preti HA, Hagemeister FB. Myelodysplasia and acute myeloid leukemia following therapy for indolent lymphoma with fludarabine, mitoxantrone, and dexamethasone (FND) plus rituximab and interferon alpha. Blood. 2005; 105:4573-5. doi:10.1182/blood-2004-08-3035 PMid:15741224 PMCid:1895007
24. Carney DA, Westerman DA, Tam CS, Milner A, Prince HM, Kenealy M, Wolf M, Januszewicz EH, Ritchie D, Came N, Seymour JF. Therapy-related myelodysplastic syndrome and acute myeloid leukemia following fludarabine combination chemotherapy. Leukemia. 2010; 24: 2056-62. doi:10.1038/leu.2010.218 PMid:20962860
25. Pedersen-Bjergaard J, Christiansen DH, Desta F, Andersen MK. Alternative genetic pathways and cooperating genetic abnormalities in the pathogenesis of therapy-related myelodysplasia and acute myeloid leukemia. Leukemia. 2006; 20:1943-9. doi:10.1038/sj.leu.2404381 PMid:16990778
26. Voso MT, D'Alò F, Greco M, Fabiani E, Criscuolo M, Migliara G, Pagano L, Fianchi L, Guidi F, Hohaus S, Leone G. Epigenetic changes in therapy-related MDS/AML. Chem Biol Interact, 2010; 184:46-9. doi:10.1016/j.cbi.2009.10.013 PMid:19874806
27. Treon SP, Gertz MA, Dimopoulos M, Anagnostopoulos A, Blade J, Branagan AR, Garcia-Sanz R, Johnson S, Kimby E, Leblond V, Fermand JP, Maloney DG, Merlini G, Morel P, Morra E, Nichols G, Ocio EM, Owen R, Stone MJ. Update on treatment recommendations from the Third International Workshop on Waldenstrom's macroglobulinemia. Blood 2006; 107: 3442-6. doi:10.1182/blood-2005-02-0833 PMid:16410453
28. Vijay A. Gertz MA, Waldenstrom Macroglobulinemia. Blood 2007; 109: 5096-103.
29. Facon T, Brouillard M, Duhamel A, Morel P, Simon M, Jouet JP, Bauters F, Fenaux P. Prognostic factors in Waldenström's macroglobulinemia: a report of 167 cases. J Clin Oncol 1993; 11: 1553-8. PMid:8336194
30. Kyle RA, Greipp PR, Gertz MA, Witzig TE, Lust JA, Lacy MQ, Therneau TM Waldenström's macroglobulinaemia: a prospective study comparing daily with intermittent oral chlorambucil. Br J Haematol. 2000; 108: 737-42. doi:10.1046/j.1365-2141.2000.01918.x PMid:10792277
31. García-Sanz R, Montoto S, Torrequebrada A, de Coca AG, Petit J, Sureda A, Rodríguez-García JA, Massó P, Pérez-Aliaga A, Monteagudo MD, Navarro I, Moreno G, Toledo C, Alonso A, Besses C, Besalduch J, Jarque I, Salama P, Rivas JA, Navarro B, Bladé J, Miguel JF. Waldenström macroglobulinaemia: presenting features and outcome in a series with 217 cases. Br J Haematol 2001, 115: 575-82. doi:10.1046/j.1365-2141.2001.03144.x PMid:11736938
32. Leblond V, Lévy V, Maloisel F, Cazin B, Fermand JP, Harousseau JL, Remenieras L, Porcher R, Gardembas M, Marit G, Deconinck E, Desablens B, Guilhot F, Philippe G, Stamatoullas A, Guibon O. Multicenter, randomized comparative trial of fludarabine and the combination of cyclophosphamide-doxorubicin-prednisone in 92 patients with Waldenström macroglobulinemia in first relapse or with primary refractory disease. Blood 2001; 98: 2640-4. doi:10.1182/blood.V98.9.2640 PMid:11675332 
33. Ghobrial IM, Fonseca R, Gertz MA, Plevak MF, Larson DR, Therneau TM, Wolf RC, Hoffmann RJ, Lust JA, Witzig TE, Lacy MQ, Dispenzieri A, Vincent Rajkumar S, Zeldenrust SR, Greipp PR, Kyle RA. Prognostic model for disease-specific and overall mortality in newly diagnosed symptomatic patients with Waldenstrom macroglobulinaemia. Br J Haematol. 2006; 132: 158-64. doi:10.1111/j.1365-2141.2006.06003.x PMid:16611306
34. Leleu X, Soumerai J, Roccaro A, Hatjiharissi E, Hunter ZR, Manning R, Ciccarelli BT, Sacco A, Ioakimidis L, Adamia S, Moreau AS, Patterson CJ, Ghobrial IM, Treon SP. Increased incidence of transformation and myelodysplasia/acute leukemia in patients with Waldenström macroglobulinemia treated with nucleoside analogs. J Clin Oncol. 2009; 27: 250-5.doi:10.1200/JCO.2007.15.1530 PMid:19064987
35. Tedeschi A, Alamos SM, Ricci F, Greco A, Morra E Fludarabine-based combination therapies for Waldenström's macroglobulinemia. Clin Lymphoma Myeloma. 2009; 9: 67-70.doi:10.3816/CLM.2009.n.017
36. Leblond V, Tamburini J, Levy V, Choquet S, Taksin AL, Maloisel F and Morel P. Incidence of Disease Transformation and Development of MDS/AML in 165 Patients with Waldenström’s Macroglobulinemia (WM) Treated with Fludarabine (F)-Based Regimen in Three Studies (French Cooperative Group on CLL/WM). Blood (ASH Annual Meeting Abstracts) 2007; 110: 1291. PMid:17485551
37. Leleu X, Soumerai J, Roccaro A, Hatjiharissi E, Hunter ZR, Manning R, Ciccarelli BT, Sacco A, Ioakimidis L, Adamia S, Moreau AS, Patterson CJ, Ghobrial IM, Treon SP. Increased incidence of transformation and myelodysplasia/acute leukemia in patients with Waldenström macroglobulinemia treated with nucleoside analogs. J Clin Oncol. 2009; 27: 250-5. doi:10.1200/JCO.2007.15.1530 PMid:19064987
38. Leblond V, Ben-Othman T, Deconinck E, Taksin AL, Harousseau JL, Delgado MA, Delmer A, Maloisel F, Mariette X, Morel P, Clauvel JP, Duboisset P, Entezam S, Hermine O, Merlet M, Yakoub-Agha I, Guibon O, Caspard H, Fort N. Activity of fludarabine in previously treated Waldenström's macroglobulinemia: a report of 71 cases. Groupe Coopératif Macroglobulinémie. J Clin Oncol. 1998; 16: 2060-4.PMid:9626204
39. Tamburini J, Lévy V, Chaleteix C, Fermand JP, Delmer A, Stalniewicz L, Morel P, Dreyfus F, Grange MJ, Christian B, Choquet S, Leblond V. Fludarabine plus cyclophosphamide in Waldenström's macroglobulinemia: results in 49 patients. Leukemia 2005; 19:1831-4. doi:10.1038/sj.leu.2403885 PMid:16121217
40. Treon SP, Branagan AR, Ioakimidis L, Soumerai JD, Patterson CJ, Turnbull B, Wasi P, Emmanouilides C, Frankel SR, Lister A, Morel P, Matous J, Gregory SA, Kimby E. Long-term outcomes to fludarabine and rituximab in Waldenström macroglobulinemia. Blood 2009; 113: 3673-8.doi:10.1182/blood-2008-09-177329 PMid:19015393 PMCid:2670786
41. Leblond V, Compain L, Levy V, Tamburini J, Delmer A, Vargaftig J, Pégourié-Bandelier B, Mahe B, Le Guill S, Tournilhac O, Brottier-Mancini E, Delarue R, Buzyn A, Maigre M, Gardin C Choquet S. Fludarabine Plus Cyclophosphamide and Rituximab In Waldenström's Macroglobulinemia: Results In 55 Patients. Blood (ASH Annual Meeting Abstracts) 2010; 116: 1757. 
42. Tedeschi A, Benevolo G, Varettoni M, Battista M, Zinzani P, Visco C, Meneghini V, Pioltelli P, Sacchi S, Ricci F, Zaja F, Nichelatti M, Lazzarino M, Vitolo U, Morra E. Fludarabine, plus cyclophosphamide and rituximab in Waldenstrom’s Macroglobulinemia: an effective but myelosuppressive regimen to be offered to advanced disease patients. Cancer in press. 2011. 
43. Rakkhit R, Delasalle KB, Gavino MB, Thomas SK, Dimopoulos MA, Hagemeister FB, Rodriguez MA, McLaughlin P, Alexanian R, Weber DM. Incidence of Transformation to Large Cell Lymphoma and to Second Malignancies in Symptomatic Patients with Waldenstrom’s Macroglobulinemia (WM) Treated with Cladribine (2-CdA) Combination Induction Therapy. Blood (ASH Annual Meeting Abstracts) 2008; 112: 3065.PMid:18650451 
44. Laszlo D, Andreola G, Rigacci L, Fabbri A, Rabascio C, Mancuso P, Pruneri G, Radice D, Pinto A, Frigeri F, Calabrese L, Billio A, Bertolini F, Martinelli G. Rituximab and subcutaneous 2-chloro-2'-deoxyadenosine combination treatment for patients with Waldenstrom macroglobulinemia: clinical and biologic results of a phase II multicenter study. J Clin Oncol. 2010; 28: 2233-8. doi:10.1200/JCO.2009.23.6315 PMid:20368573
45. Robak T, Blonski JZ, Gora-Tybor J, Kasznicki M, Konopka L, Ceglarek B, Komarnicki M, Lewandowski K, Hellmann A, Lewandowski K, Moskwa A, Dmoszynska A, Sokolowska B, Dwilewicz-Trojaczek A, Tomaszewska A, Sulek K, Calbecka M. Second malignancies and Richter's syndrome in patients with chronic lymphocytic leukaemia treated with cladribine. Eur J Cancer 2004; 40: 383-9. doi:10.1016/j.ejca.2003.09.031PMid:14746857
46. Seymour J. and Campbell J. In: Cheson B.D, ed., Richter’s Syndrome in Chronic Lymphocytic Leukemia (Marcel Dekker, Nek York, Basel). 2002; 459-83. 
47. Giles FJ, O'Brien SM, Keating MJ. Chronic lymphocytic leukemia in (Richter's) transformation. Semin Oncol. 1998; 25: 117-25. PMid:9482533
48. Wiernik PH. Second neoplasms in patients with chronic lymphocytic leukemia. Curr Treat Options Oncol. 2004; 5: 215-23. doi:10.1007/s11864-004-0013-7 PMid:15115650
49. Travis LB, Curtis RE, Hankey BF, Fraumeni JF. Second cancers in patients with chronic lymphocytic leukemia. J Natl Cancer Inst. 1992; 84: 1422-7. doi:10.1093/jnci/84.18.1422
50. Dighiero G, Maloum K, Desablens B, Cazin B, Navarro M, Leblay R, Leporrier M, Jaubert J, Lepeu G, Dreyfus B, Binet JL, Travade P. Chlorambucil in indolent chronic lymphocytic leukemia. French Cooperative Group on Chronic Lymphocytic Leukemia. N Engl J Med. 1998; 338: 1506-14.doi:10.1056/NEJM199805213382104 PMid:9593789
51. Robertson LE, Estey E, Kantarjian H, Koller C, O'Brien S, Brown B, Keating MJ. Therapy-related leukemia and myelodysplastic syndrome in chronic lymphocytic leukemia. Leukemia 1994; 8: 2047-51. PMid:7807993
52. Keating MJ, O'Brien S, Lerner S, Koller C, Beran M, Robertson LE, Freireich EJ, Estey E, Kantarjian H. Long term follow-up of patients with chronic lymphocytic leukemia (CLL) receiving fludarabine regimens as initial therapy. Blood 1998; 92: 1165-71. PMid:9694704
53. Leporrier M, Chevret S, Cazin B, Boudjerra N, Feugier P, Desablens B, Rapp MJ, Jaubert J, Autrand C, Divine M, Dreyfus B, Maloum K, Travade P, Dighiero G, Binet JL, Chastang C. Randomized comparison of fludarabine, CAP, and ChOP in 938 previously untreated stage B and C chronic lymphocytic leukemia patients. Blood 2001; 98:2319-25.doi:10.1182/blood.V98.8.2319 PMid:11588025
54. Johnson S, Smith AG, Löffler H, Osby E, Juliusson G, Emmerich B, Wyld PJ, Hiddemann W. Multicentre prospective randomised trial of fludarabine versus cyclophosphamide, doxorubicin, and prednisone (CAP) for treatment of advanced-stage chronic lymphocytic leukaemia. The French Cooperative Group on CLL. Lancet 1996; 347:1432-8. PMid:8676625
55. Cheson BD, Vena DA, Barrett J, Freidlin B. Second malignancies as a consequence of nucleoside analog therapy for chronic lymphoid leukemias. J Clin Oncol 17:2454-60, 1999.PMid:10561309
56. Ricci F, Tdeschi A, Morra E, Montillo M. Fludarabine in the treatment of chronic lymphocytic leukemia: a review. Therapeutics and Clinical Risk Management 2009; 5: 187-207.
57. Morrison VA, Rai KR, Peterson BL, Kolitz JE, Elias L, Appelbaum FR, Hines JD, Shepherd L, Larson RA, Schiffer CA. Therapy-related myeloid leukemias are observed in patients with chronic lymphocytic leukemia after treatment with fludarabine and chlorambucil: results of an intergroup study, cancer and leukemia group B 9011. J Clin Oncol. 2002; 20: 3878-84.doi:10.1200/JCO.2002.08.128 PMid:12228208
58. Smith MR, Neuberg D, Flinn IW, Grever MR, Bennett JM, Dewald G, Paietta EM, Litzow MR, Rowe JM, Lucas D, Kitada S, Jelinek DF, Gribben JG, Byrd JC, Reed JC, Hussein MA, Appelbaum FR, Larson RA, Moore DF, and Tallman MS. Increased Incidence of Therapy Related Myeloid Neoplasia (t-MN) After Initial Therapy for CLL with Fludarabine-Cyclophosphamide (FC) Vs Fludarabine (F): Long-Term Follow-up of US Intergroup Study E2997. Blood (ASH Annual Meeting Abstracts) 2010 116: Abstract 924. 
59. Badoux XC, Keating MJ, Wang X, O'Brien SM, Ferrajoli A, Faderl S, Burger J, Koller C, Lerner S, Kantarjian H, Wierda WG. Fludarabine, cyclophosphamide and rituximab chemoimmunotherapy is highly effective treatment for relapsed patients with CLL. Blood 2011; 117: 3016-24. doi:10.1182/blood-2010-08-304683 PMid:21245487
60. Woyach JA, Ruppert AS, Heerema NA, Peterson BL, Gribben JG, Morrison VA, Rai KR, Larson RA, Byrd JC. Chemoimmunotherapy With Fludarabine and Rituximab Produces Extended Overall Survival and Progression-Free Survival in Chronic Lymphocytic Leukemia: Long-Term Follow-Up of CALGB Study 9712. J Clin Oncol. 2011; Feb 14 [Epub ahead of print]
61. Gribben JG, Zahrieh D, Stephans K, Bartlett-Pandite L, Alyea EP, Fisher DC, Freedman AS, Mauch P, Schlossman R, Sequist LV, Soiffer RJ, Marshall B, Neuberg D, Ritz J, Nadler LM. Autologous and allogeneic stem cell transplantations for poor-risk chronic lymphocytic leukemia. Blood 2005; 106: 4389-96.doi:10.1182/blood-2005-05-1778 PMid:16131571 PMCid:1895235
62. Dreger P, Döhner H, Greinix H, McClanahan F, Hensel M, Hertenstein B, Dührsen U, Hentrich M, Trümper L, Sonnen R, Emmerich B, Knauf WU, Hopfinger G, Hallek M, Kneba M, Schmitz N and Stilgenbauer S. Early Autologous Stem Cell Transplantation (autoSCT) May Overcome the Adverse Impact of Del 11q- in Poor-Risk Chronic Lymphocytic Leukemia (CLL): Results From the GCLLSG CLL3 Trial. Blood (ASH Annual Meeting Abstracts) 2009; 114: 879. 
63. Milligan DW, Fernandes S, Dasgupta R, Davies FE, Matutes E, Fegan CD, McConkey C, Child JA, Cunningham D, Morgan GJ, Catovsky D. National Cancer Research Institute Haematological Studies Group. Results of the MRC pilot study show autografting for younger patients with chronic lymphocytic leukemia is safe and achieves a high percentage of molecular responses.Blood 2005; 105: 397-404. doi:10.1182/blood-2004-01-0298 PMid:15117764
64. Michallet M, Dreger P, Sutton L, Brand R, Richards S, van Os M, Sobh M, Choquet S, Corront B, Dearden C, Gratwohl A, Herr W, Catovsky D, Hallek M, de Witte T, Niederwieser D, Leporrier M, Milligan D. Autologous hematopoietic stem cell transplantation in chronic lymphocytic leukemia: results of European intergroup randomized trial comparing autografting versus observation. Blood 2011; 117: 1516-21. doi:10.1182/blood-2010-09-308775 PMid:21106985