Clinical Lymphoma and Myeloma最新文献

Acute leukemias are complex diseases on multiple levels, and laboratory efforts over the past 3 decades have focused on better understanding of the molecular underpinnings and their stem cell biology. We now have a panoply of technologic advances that allow us to characterize individual leukemias by molecular profiles that relate directly to clinical behavior, to detect minimal residual disease, and to begin to develop “targeted” therapeutic strategies based on molecular considerations. There are a number of challenges surrounding this task: first, how to combine these agents with traditional chemotherapeutics and/or with each other to maximize leukemic cell kill and increase the cure rate; second, how to use these targeted agents in the minimal residual disease with potential curative intent; third, for patients unable to tolerate or unlikely to benefit from aggressive approaches, how to use one or more of these agents to reduce tumor bulk and either permit some restoration of normal marrow function or induce morphologic and functional differentiation of the leukemic clone to overcome the leukemia-associated bone marrow failure; and lastly, how to measure the effects of these agents on the molecular and cellular biologic levels in ways that correlate with and might even predict overall clinical outcome. These challenges are further complicated by the inherent heterogeneity in host biology; disease etiology and biology; and interactions among host, disease, and treatment that ultimately determine individual clinical outcomes. Toward this end, we will discuss selected issues surrounding new clinical trial designs and the development of clinically relevant molecular endpoints that might facilitate the development of new treatment approaches that will improve the outlook for adults with acute leukemias.

Lenalidomide is an immunomodulatory drug (IMiD™) with erythropoietic activity in myelodysplastic syndromes (MDS) that is karyotype dependent. The MDS-003 multicenter registration trial in deletion of chromosome 5q (del[5q]) showed that lenalidomide suppresses the del(5q) clone in patients who achieve transfusion independence and is a prerequisite for sustained restoration of effective erythropoiesis. Long-term outcome data indicate that cytogenetic response to lenalidomide might confer a survival advantage compared with cytogenetic nonresponders, with a corresponding reduced risk for acute myeloid leukemia (AML) progression. In lower-risk, transfusion-dependent patients with MDS without del(5q), lenalidomide has significant, albeit less erythropoietic, activity that could relate to dual effects on both the MDS clone and the bone marrow environment. The most common adverse effects are neutropenia and thrombocytopenia, which occur early and with greater frequency in patients with del(5q), consistent with the drug's action to suppress the MDS clone. Combination strategies are now in both MDS and AML that could further broaden the therapeutic potential of lenalidomide.

Bacterial infection is the most common complication of chemotherapy-induced neutropenia particularly in patients with hematologic malignancies. Bacterial infections predominate during the initial phases of neutropenic episodes. The spectrum of bacterial infection continues to evolve globally and locally at the institutional level, as do patterns of antimicrobial susceptibility/resistance. These trends are often associated with local treatment practices (eg, use of antimicrobial prophylaxis, open versus restricted formularies, clinical pathways and/or guidelines) and have a significant effect on the nature of empiric antimicrobial therapy. Increasing rates of resistance among gram-positive and gram-negative bacteria are posing new therapeutic challenges. These challenges can to some extent be overcome by new drug development. Many novel agents for the treatment of resistant gram-positive infections have been developed and are being evaluated in clinical trials. Newer agents for the treatment of Clostridium difficile associated diarrhea are also in the pipeline. Far fewer options to treat multi-drug resistant gram-negative infections exist, and new drug development is lagging behind. Consequently, the judicious use of currently available agents is essential. This is best achieved by the development of multidisciplinary antibiotic stewardship teams that gather baseline data, make recommendations for appropriate antimicrobial usage, and provide monitoring and feedback services to clinical care providers. Along with strict adherence to infection control policies, antimicrobial stewardship provides the best strategies for the management of infectious complications in patients with hematologic malignancies and other high-risk settings.

Burkitt lymphoma/leukemia (BL) has become a very curable mature B-cell neoplasm. Current standard regimens, focused on the unique characteristics of this disease, are composed of cyclical intensive chemotherapy and aggressive intrathecal prophylaxis. Using this approach, complete response rates of 80%–90% are routinely achieved, and survival is now approaching 80% with the addition of rituximab to these intensive regimens. Prophylactic cranial irradiation and prolonged maintenance have no proven benefit and are not recommended. The more widespread use of highly active antiretroviral therapy in the HIV patient with BL has allowed the use of similar aggressive therapies that are used for the non-HIV BL patients, with commensurate improvements in outcomes in this high-risk population. Future improvements for patients with BL could rely on standardization of gene expression profiling (to ensure more accurate diagnoses and prognostication of disease and to understand mechanisms of treatment resistance) and to develop novel biologically targeted approaches to treatment. The next generation of clinical trials to further improve survival will have the challenge of identifying high-risk patients who might be candidates for novel agents that could be incorporated into existing regimens with the goal of curing all patients with this disease.

Anemia is the most frequent peripheral cytopenia observed in myelodysplastic syndromes (MDS) and has been recognized among the most important factors affecting the outcome of patients with MDS. In patients who are not candidates for potentially curative approaches, therapeutic options for symptomatic anemia include red blood cell (RBC) transfusion and iron chelation, hematopoietic growth factors, immunosuppression, immune-modulatory drugs, and hypomethylating agents. In about 40% of patients, regular RBC transfusions are the only therapeutic option that can be offered. The onset of a regular transfusion requirement significantly worsens the survival of patients with MDS. Transfusion-dependent patients invariably develop secondary iron overload. Elevated serum ferritin was proven to be associated with worse survival in transfusion-dependent patients, and recent data obtained using magnetic resonance imaging show both hepatic and myocardial iron accumulation in heavily transfused patients. According to evidence-based guidelines, patients with sideroblastic anemia, 5q- syndrome, or other forms of refractory anemia, in whom long-term transfusion therapy is likely, are recognized as the best candidates to receive iron chelation therapy. In addition, patients who are candidates for allogeneic stem cell transplantation might also benefit from chelation therapy because iron overload is associated with increased transplantation-related mortality. RBC transfusions and iron chelation are the mainstay of therapy for many individuals with MDS. However, critical issues remain to be clarified in order to optimize treatment, including the identification of target hemoglobin levels to prevent anemia-related morbidity and more accurate information on the effect of iron-mediated organ damage on the outcome of patients with MDS.

Patients with chronic lymphocytic leukemia (CLL) with high-risk cytogenetic features such as del(17p13) have limited treatment options and decreased overall survival. Dysfunction of p53 leads to resistance to fludarabine-based therapies. Cyclin-dependent kinase inhibitors (CDKi) are a novel class of agents that induce apoptosis in CLL cells independent of p53 mutational status. The synthetic flavone flavopiridol demonstrated promising in vitro activity in CLL. In initial phase I studies using a continuous infusion dosing schedule in a variety of malignancies, no clinical activity was observed. Detailed pharmacokinetic modeling led to the development of a novel dosing schedule designed to achieve target drug concentrations in vivo. In phase I testing, this dosing schedule resulted in acute tumor lysis syndrome (TLS) as the dose-limiting toxicity. With the implementation of a standardized protocol to prevent severe TLS, flavopiridol was administered safely, and responses were observed in heavily pretreated, fludarabine-refractory patients, cytogenetically high-risk patients, and patients with bulky lymphadenopathy. In a pharmacokinetic analysis, flavopiridol area under the plasma concentration-time curve (AUC) correlated with clinical response and cytokine release syndrome. Phase II studies are under way with encouraging preliminary results. Flavopiridol is currently under active investigation in combination with other agents and as a means to eradicate minimal residual disease in patients following cytoreductive chemotherapy. Several other investigational CDKi in preclinical and early clinical development are briefly discussed in this review.

Though B-chronic lymphocytic leukemia (CLL) is known to be a heterogeneous disease, only recently has the familial component of CLL been more thoroughly investigated. This entity is seen in approximately 5%–10% of all patients with CLL and can be associated with earlier age of diagnosis, higher female prevalence, and increased incidence of other lymphoproliferative disorders (LPDs), such as non-Hodgkin lymphoma and the more recently described monoclonal B-cell lymphocytosis CLL in family members. The prognostic parameters and clinical course of familial CLL is not clearly distinguishable from that of sporadic disease. In addition, it is not clear that the treatment responses for progressive disease has any discernible difference in familial versus sporadic CLL. The genetic etiology of CLL is unknown, and early work on familial CLL has not yet uncovered any obvious gene or group of genes that can be clearly related to the pathophysiology of CLL. However, the detailed genetic study of familial CLL is likely to be critical in uncovering relevant genes. At present it is best to indicate to concerned CLL patients that their relatives are at relatively low risk of developing CLL or other LPDs.

Thrombopoietin (TPO) is the physiologic regulator of platelet production and works by binding to its receptor on megakaryocyte precursor cells, thereby activating a large number of antiapoptotic and cell maturation pathways. “First-generation” recombinant forms of TPO were developed over a decade ago and were found to increase the platelet count in patients undergoing nonmyeloablative chemotherapy, in patients with immune thrombocytopenic purpura (ITP) and myelodysplasia, as well as in platelet apheresis donors. Thrombopoietin did not improve platelet counts in patients undergoing stem cell transplantation or acute leukemia induction. Further development ended when antibodies formed against one of the recombinant proteins. Subsequently, 2 “second-generation” TPO mimetics have been developed and are entering clinical practice: romiplostim and eltrombopag. Romiplostim is an injectable peptide TPO mimetic that activates the TPO receptor just like native TPO. Eltrombopag is an oral nonpeptide TPO mimetic that activates the TPO receptor by binding to a different region of the TPO receptor that does not compete with TPO binding. Both increased the platelet counts in healthy subjects and in over two thirds of patients with ITP both before and after splenectomy; responses were maintained for at least 1 year. Romiplostim and eltrombopag are now US Food and Drug Administration approved for the second-line treatment of patients with ITP. Adverse events have been few, but long-term assessment for reticulin formation, increased bone marrow blasts, and thromboembolism is ongoing. Studies are under way to assess the efficacy of these drugs in the treatment of other thrombocytopenic disorders associated with chemotherapy, myelodysplasia, and chronic hepatitis.

T-cell prolymphocytic leukemia is a rare postthymic malignancy with distinctive clinical, morphologic, immunophenotypic, and cytogenetic features. The clinical course is typically aggressive with poor response to conventional chemotherapy and short survival. Treatment with purine analogues and alemtuzumab has resulted in significantly higher response rates and improved survival. Nevertheless, responses are relatively short, and the only potential curative treatment is allogeneic stem cell transplantation. The age and comorbidities of many of the patients has limited this option, but the growing use of nonmyeloablative transplantation has now widened the patient eligibility for this approach.

Recent seminal discoveries have significantly advanced the field of stem cell research and received worldwide attention. Improvements in somatic cell nuclear transfer (SCNT) technology, enabling the cloning of Dolly the sheep, and the derivation and differentiation of human embryonic stem cells raised hopes that normal cells could be generated to replace diseased or injured tissue. At the same time, in vitro and in vivo studies demonstrated that somatic cells of one tissue are capable of generating cells of another tissue. It was theorized that any cell might be reprogrammed, by exposure to a new environment, to become another cell type. This concept contradicts two established hypotheses: (1) that only specific tissues are generated from the endoderm, mesoderm, and ectoderm and (2) that tissue cells arise from a rare population of tissue-specific stem cells in a hierarchical fashion. SCNT, cell fusion experiments, and most recent gene transfer studies also contradict these hypotheses, as they demonstrate that mature somatic cells can be reprogrammed to regain pluripotent (or even totipotent) stem cell capacity. On the basis of the stem cell theory, hierarchical cancer stem cell differentiation models have been proposed. Cancer cell plasticity is an established phenomenon that supports the notion that cellular phenotype and function might be altered. Therefore, mechanisms of cellular plasticity should be exploited and the clinical significance of the cancer stem cell theory cautiously assessed.