Report of a European consensus workshop to develop recommendations for the optimal use of 90Y-ibritumomab tiuxetan (Zevalin®) in lymphoma

Monoclonal Antibodies: A Prospective and Retrospective View

BACKGROUND

Monoclonal Antibodies (mAbs) represent one of the most important classes of biotherapeutic agents. They are used to cure many diseases, including cancer, autoimmune diseases, cardiovascular diseases, angiogenesis-related diseases and, more recently also haemophilia. They can be highly varied in terms of format, source, and specificity to improve efficacy and to obtain more targeted applications. This can be achieved by leaving substantially unchanged the basic structural components for paratope clustering.

OBJECTIVES

The objective was to trace the most relevant findings that have deserved prestigious awards over the years, to report the most important clinical applications and to emphasize their latest emerging therapeutic trends.

RESULTS

We report the most relevant milestones and new technologies adopted for antibody development. Recent efforts in generating new engineered antibody-based formats are briefly reviewed. The most important antibody-based molecules that are (or are going to be) used for pharmacological practice have been collected in useful tables.

CONCLUSION

The topics here discussed prove the undisputed role of mAbs as innovative biopharmaceuticals molecules and as vital components of targeted pharmacological therapies.

Theranostic radiopharmaceuticals: established agents in current use

Although use of the term "theranostic" is relatively recent, the concept goes back to the earliest days of nuclear medicine, with the use of radioiodine for diagnosis and therapy of benign and malignant thyroid disease being arguably the most successful molecular radiotherapy in history. A diagnostic scan with ¹²³I-, ¹²⁴I-, or a low activity of ¹³¹I-iodide is followed by therapy with high activity ¹³¹I-iodide. Similarly, adrenergic tumours such as phaeochromocytoma and neuroblastoma can be imaged with ¹²³I-metaiodobenzylguanidine and treated with ¹³¹I-metaiodobenzylguanidine. Bone scintigraphy can be used to select patients with painful bone metastases from prostate cancer who may benefit from treatment with beta- or alpha-particle emitting bone seeking agents, the most recent and successful of which is ²²³Ra radium chloride. Anti-CD20 monoclonal antibodies can be used to image and treat non-Hodgkins lymphoma, though this has not been as commercially successful as initially predicted. More recently established theranostics include somatostatin receptor targeting peptides for diagnosis and treatment of neuroendocrine tumours with agents such as ⁶⁸Ga-DOTATATE and ¹⁷⁷Lu-DOTATATE, respectively. Finally, agents which target prostate-specific membrane antigen are becoming increasingly widely available, despite the current lack of a commercial product. With the recent licensing of the somatostatin peptides and the rapid adoption of ⁶⁸Ga- and ¹⁷⁷Lu-labelled prostate-specific membrane antigen targeting agents, we have built upon the experience of radioiodine and are already seeing a great expansion in the availability of widely accepted theranostic radiopharmaceuticals.

Consequences of radiopharmaceutical extravasation and therapeutic interventions: a systematic review

Purpose

Radiopharmaceutical extravasation can potentially lead to severe soft tissue damage, but little is known about incidence, medical consequences, possible interventions, and effectiveness of these. The aims of this study are to estimate the incidence of extravasation of diagnostic and therapeutic radiopharmaceuticals, to evaluate medical consequences, and to evaluate medical treatment applied subsequently to those incidents.

Methods

A sensitive and elaborate literature search was performed in Embase and PubMed using the keywords “misadministration”, “extravasation”, “paravascular infiltration”, combined with “tracer”, “radionuclide”, “radiopharmaceutical”, and a list of keywords referring to clinically used tracers (i.e. “Technetium-99m”, “Yttrium-90”). Reported data on radiopharmaceutical extravasation and applied interventions was extracted and summarised.

Results

Thirty-seven publications reported 3016 cases of diagnostic radiopharmaceutical extravasation, of which three cases reported symptoms after extravasation. Eight publications reported 10 cases of therapeutic tracer extravasation. The most severe symptom was ulceration. Thirty-four different intervention and prevention strategies were performed or proposed in literature.

Conclusions

Extravasation of diagnostic radiopharmaceuticals is common. ^99mTc, ¹²³I, ¹⁸F, and ⁶⁸Ga labelled tracers do not require specific intervention. Extravasation of therapeutic radiopharmaceuticals can give severe soft tissue lesions. Although not evidence based, surgical intervention should be considered. Furthermore, dispersive intervention, dosimetry and follow up is advised. Pharmaceutical intervention has no place yet in the immediate care of radiopharmaceutical extravasation.

[Extravasation of radiopharmaceuticals: preventive measures and management recommended by SoFRa (Société Française de Radiopharmacie)]

Radiopharmaceuticals extravasation is rare but may have serious clinical issues. Because no specific recommendations are being proposed to date, the goals of our working group created within the French Society of Radiopharmacy are to determine preventive measures and to establish a pragmatic management of extravasation of these drugs. Our preventive measures are to recognize the symptoms (erythema, venous discoloration, swelling), to know the risk factors (which are related to radiopharmaceutical, patient, site of injection, injection technique) and severity (from erythema to skin necrosis, depending on the radionuclide) and how to avoid them (training and awareness of staff, choice of injection site, route of drug administration test, use of a catheter for administration of therapeutic radiopharmaceuticals). Management should be immediate. It can be facilitated by a specific emergency kit. General measures recommended are the immediate cessation of injection, aspiration of fluid extravasation, delimitation of the extravasated area with an indelible pen, informing the doctor. Specific measures taking into account the radiotoxicity of the radionuclide and the type of radiopharmaceutical were also established. The patient should be informed by the doctor about the risks and how to take care of. Traceability of the incident must be ensured. A multidisciplinary reflexion is essential to manage the extravasation as early and effectively as possible.

Yttrium-90 ibritumomab tiuxetan plus busulfan, cyclophosphamide, and etoposide (BuCyE) versus BuCyE alone as a conditioning regimen for non-Hodgkin lymphoma

Background

Radioimmunotherapy agents have a highly significant role in autologous stem cell transplantation as they improve tolerability and increase the efficacy of the conditioning regimen.

Methods

We retrospectively analyzed the efficacy and toxicity of yttrium-90 ibritumomab tiuxetan (Zevalin) combined with intravenous busulfan, cyclophosphamide, and etoposide (Z-BuCyE) compared with those of BuCyE alone followed by autologous stem cell transplantation in patients with relapsed or refractory B-cell non-Hodgkin lymphoma (NHL). The efficacy, toxicity, and engraftment characteristics were compared between 19 patients who received Z-BuCyE and 19 historical controls who received BuCyE.

Results

The 2 treatment groups shared similar baseline characteristics. The median time to platelet engraftment (>20×10⁹/L) and neutrophil engraftment (>0.5×10⁹/L) did not significantly differ between the Z-BuCyE group (12 days and 10 days, respectively) and the BuCyE group (12 days and 10 days, respectively). No significant differences were observed between the groups with respect to toxicities and treatment-related mortality. The median follow-up period was 30.4 months, and median event-free survival was generally better in the Z-BuCyE group (12.5 months) vs. the BuCyE group (6.2 months, P=0.236). No significant difference in overall survival between the groups was noted.

Conclusion

Adding ibritumomab tiuxetan to BuCyE high-dose chemotherapy may benefit patients with relapsed or refractory B-cell NHL with no risk of additional toxicity.

Yttrium-90 (90Y) in the principal radionuclide therapies: an efficacy correlation between peptide receptor radionuclide therapy, radioimmunotherapy and transarterial radioembolization therapy. Ten years of experience (1999-2009)

The clinical application of the pure beta emitter (90)Y constitutes a fundamental advancement in non-invasive medicine. Nowadays, mainly three oncological therapies exploit the intrinsic emissive characteristic of (90)Y. Radionuclide therapies include peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumour (NET) treatment, radioimmunotherapy (RIT) in non-Hodgkin's lymphoma (NHL) treatment and transarterial radioembolization therapy (TARET) in unresectable hepatocellular carcinoma (HCC) and liver metastatic colorectal cancer (mCRC) treatment. The last ten years of clinical experience from E-PubMed research have been reviewed and an efficacy correlation between (90)Y-therapies has shown a better objective response rate for RIT (ORR 80±15%; range 53-100) compared to PRRT (ORR 23.5±14%; range 9-50), and TARET (ORR for mCRC, 40±25%; range 19-91, and ORR for HCC, 42±20%; range 20-82). This review reports on the state of the art of the efficacy of (90)Y-therapies from the last decade and discusses new perspectives of therapeutic development.

Changing therapeutic landscape--the last decade

Undoubtedly the most important event in the previous decade in lymphoma treatment was the establishment of immunotherapy as a prime modality. Addition of rituximab improves survival in almost every group of patients with CD20+ tumors. This has led to the appearance of a number of "me too" monoclonal antibodies (MoAbs) as well as MoAbs directed against other antigens whose usefulness remains to be proven during the next decade. We have also seen the raise and, probably unwarranted, fall of radioimmunotherapy. Conventional radiotherapy is losing ground. Regarding chemotherapy, the success of attempts to supplant R-CHOP-21 for front-line treatment of DLBCL with more dose-dense or dose-intense regimens remains doubtful and this issue is still unresolved. Bendamustine appeared as possibly the most effective cytotoxic agent for treatment of indolent lymphomas, while treatment of HL is becoming more tailored to prognostic features. This decade has also seen the advent of targeted drugs for lymphoma treatment. Their real impact will become known in the years to come. Finally, we may hope that advances in understanding the biology of lymphomas, made in the last decade, will help resolve remaining critical issues, treatment of T-NHLs and high-risk DLBCLs, being probably the most prominent.

Diversity in antibody-based approaches to non-Hodgkin lymphoma

Non-Hodgkin lymphoma (NHL) remains one of the most common cancers in the US, with survival dependent on the type and stage of disease. B-cell lymphomas account for approximately 85% of all cases of NHL, and are commonly treated with chemotherapy, or monoclonal antibodies (mAbs) that target CD20 antigens on the surface of malignant tumors. The use of mAbs, either as single agents or in combination with chemotherapy, has made a huge impact on NHL survival rates. Rituximab remains the most commonly used and established mAb, and is used in a wide range of NHLs, but does not produce an effective therapeutic response in all patients. Novel therapeutics with enhanced binding affinity or alternative antigen targets are currently in development and in some cases have demonstrated improved efficacy over currently available treatments. Radioimmunotherapy has been included in transplant conditioning regimens to improve long-term disease control while limiting toxicity. These regimens have been safe, effective, and feasible, and are therefore promising for patients who cannot tolerate high-dose chemotherapy and/or total body irradiation.

Evolution of anti-CD20 monoclonal antibody therapeutics in oncology

Approval of an anti-CD20 chimeric monoclonal antibody, rituximab, has revolutionized cancer treatment and also validated CD20 targeting for providing benefit and improvement of overall response rate in B cell malignancies. Although many patients have benefited from the treatment of rituximab, there are still significant numbers of patients who are refractory or develop resistance to the treatment. Here we discuss pre-clinically well-defined potential mechanisms of action for rituximab and review the ways next generation anti-CD20 monoclonal antibodies can potentially exploit them to further enhance the treatment of B cell malignancies. Although the relative importance of each of these mechanism remains to be established in the clinic, well-designed clinical trials will help to define the efficacy and understanding of which effector activity of modified next generation anti-CD20 mAb will be important in the treatment of B-cell malignancies.

Eradication of CD19+ leukemia by targeted calicheamicin θ

Children with relapsed and refractory acute lymphoblastic leukemia (ALL) still face a critical prognosis. We tested the hypothesis that targeted calicheamicin theta (θ) using an anti-CD19-immunoconjugate may provide an effective treatment strategy for CD19(+) ALL. Calicheamicin θ is a rationally designed prodrug of the natural enediyene calicheamicin γ, obtained by total synthesis. It offers the advantage of increased in vivo stability and 1000-fold higher antitumor potency over calicheamicin γ. First, we demonstrate efficacy of calicheamicin θ against primary pre-B leukemic cells and multidrug-resistant leukemia cell lines (IC(50) = 10(-9) to 10(-12) M). Second, conjugation of calicheamicin θ to an internalizing murine anti-CD19 monoclonal antibody was demonstrated to affect neither calicheamicin θ mediated cytotoxicity nor binding of the antibody to the target molecule. Third, anti-CD19-calicheamicin θ immunoconjugate revealed a maximum tolerated dose of 10 μg/kg and CD19-specific and long-lasting eradication of established leukemia was demonstrated in a xenograft model. Finally, we show that the antileukemic effect of anti-CD19-calicheamicin θ is mediated by induction of apoptosis proceeding through the caspase-mediated mitochondrial pathway. On the basis of these results, we conclude that anti-CD19-calicheamicin θ immunoconjugates may offer a novel and effective approach for the treatment of relapsed CD19(+) ALL.

Dexa-BEAM as salvage therapy in patients with primary refractory aggressive Non-Hodgkin lymphoma

Although aggressive NHL in relapse after remission can still be cured by second-line treatment followed by high-dose therapy and autologous stem cell transplantation, the long-term prognosis of patients who fail to obtain remission after first-line therapy remains extremely poor. We retrospectively evaluated a series of 29 consecutive patients with primary refractory high-grade NHL who were treated with Dexa-BEAM (DB) as uniform salvage therapy at a single institution. Twenty-nine patients with aggressive NHL primary refractory to CHOP or CHOP-like induction therapy with a median age of 47 (range, 22 - 64) years received 1 - 2 cycles of DB and were candidates for subsequent autologous stem cell (PBSC) mobilization and transplantation (PBSCT). Follow-up of all patients was updated in March 2004. Eight of 29 patients (28%) responded to one cycle of DB (1 complete/7 partial remissions); 2 of whom are alive after PBSCT (1 autologous/1 matched unrelated donor), 1 patient died after autologous PBSCT. Reasons for failure to proceed to high-dose therapy in spite of response to DB were recurrent progressive disease (n = 2), septicemia (n = 1), and allogeneic transplant-related mortality after mobilization failure to DB (n = 2). Twenty-one patients failed to respond to DB and died of progressive disease. Overall survival was 7% after 41 months. We conclude that Dexa-BEAM salvage therapy is not effective in patients with truly primary refractory high-grade NHL. The efficiency of rituximab combined with Dexa-BEAM or novel chemotherapeutic strategies needs to be established.

Follicular lymphoma: today's treatments and tomorrow's targets

Over the past two decades, the incidence of follicular lymphoma has increased. Contemporary treatments include combinations of chemotherapy and monoclonal antibodies, radioimmunotherapy, new targeted agents and stem-cell transplantation. Prognostic tools are becoming more important in helping clinicians and patients decide on the most appropriate therapeutic regimens. Gene expression profiling and biomarkers are promising additions to this armamentarium. When patients do require therapy, the addition of rituximab to chemotherapy seems to improve remission duration and may improve overall survival. Radioimmunotherapy capitalises on the capacity to target radiation directly to malignant cells, and is currently approved for the treatment of relapsed/refractory follicular lymphoma. Further investigation is needed to clarify the role of stem-cell transplantation in follicular lymphoma. Only well-designed clinical trials can provide answers to the many questions that remain regarding the optimal treatment and sequence of treatments for patients with follicular lymphoma.

Current status and future perspectives for yttrium-90 ((90)Y)-ibritumomab tiuxetan in stem cell transplantation for non-Hodgkin's lymphoma

Haematopoietic SCT is currently considered a therapeutic option mainly in relapsed or refractory non-Hodgkin's lymphoma (NHL) owing to high post-transplantation relapse rates and significant toxicity of conventional myeloablative conditioning for allogeneic SCT. Radiolabelled immunotherapy combines the benefits of monoclonal antibody targeting with therapeutic doses of radiation, and is a promising advance in the treatment of malignant lymphomas. It is now under investigation as a component of conditioning prior to SCT, with the aim of improving outcomes following SCT without increasing the toxicity of high-dose chemotherapy pre-transplant conditioning. An expert panel met at a European workshop in November 2006 to review the latest data on radiolabelled immunotherapy in the transplant setting, and its potential future directions, with a focus on (90)Y-ibritumomab tiuxetan. They reviewed data on the combination of standard/high/escalating dose (90)Y-ibritumomab tiuxetan with high-dose chemotherapy, and high/escalating dose (90)Y-ibritumomab tiuxetan as the sole myeloablative agent, prior to autologous SCT, and also (90)Y-ibritumomab tiuxetan as a component of reduced intensity conditioning prior to allogeneic SCT. The preliminary data are highly promising in terms of conditioning tolerability and patient outcomes following transplant; further phase II studies are now needed to consolidate these data and to investigate specific patient populations and NHL subtypes.

Yttrium-90-ibritumomab tiuxetan (Zevalin) combined with high-dose BEAM chemotherapy and autologous stem cell transplantation for chemo-refractory aggressive non-Hodgkin's lymphoma

OBJECTIVE

To determine the safety and outcome following standard-dose ibritumomab tiuxetan followed by BEAM high-dose chemotherapy and autologous stem cell transplantation (ASCT) in patients with chemo-refractory aggressive non-Hodgkin's lymphoma.

PATIENTS AND METHODS

The study included 23 patients, median age 55 years (range, 35-66) with chemo-refractory lymphoma, either primary refractory (n = 11) or in refractory relapse (n = 12). Rituximab 250 mg/m(2) followed by ibritumomab tiuxetan 0.4 mCi/kg were given on day -14 and high-dose BEAM chemotherapy started on day -6.

RESULTS

All patients engrafted. Twenty-one patients are evaluable for response; 11 achieved CR, 9 achieved PR, 5 of whom converted to CR with additional radiation therapy (overall CR rate 76%). With a median follow-up of 17 months (range, 4-27) 16 patients are alive and 12 are progression-free. The estimated 2-year overall and progression-free survival are 67% (95% CI, 46-87%) and 52% (95% CI, 31-72%), respectively. The day-100 rate of treatment-related mortality was 9% (95% CI, 2-33%) and the 2-year cumulative incidence of relapse was 31% (95% CI, 17-57%). Extensive prior therapy (>3 lines), high LDH and IPI score at ASCT, bulky disease, and progression during last chemotherapy were risk factors for reduced survival.

CONCLUSION

Ibritumomab tiuxetan-BEAM and ASCT is relatively safe and may improve outcome in patients with refractory lymphoma. Although excess nonrelapse mortality can not be ruled out, relapse rate was relatively low, resulting in improved outcome. Standard-risk patients with chemo-sensitive disease may also benefit from ibritumomab tiuxetan-BEAM and ASCT. This hypothesis merits further study in larger-scale prospective randomized studies.

EANM procedure guideline for radio-immunotherapy for B-cell lymphoma with 90Y-radiolabelled ibritumomab tiuxetan (Zevalin)

BACKGROUND

In January 2004, EMEA approved 90Y-radiolabelled ibritumomab tiuxetan, Zevalin, in Europe for the treatment of adult patients with rituximab-relapsed or -refractory CD20+ follicular B-cell non-Hodgkin's lymphoma. The number of European nuclear medicine departments using Zevalin is continuously increasing, since the therapy is often considered successful. The Therapy, Oncology and Dosimetry Committees have worked together in order to define some EANM guidelines on the use of Zevalin, paying particular attention to the problems related to nuclear medicine.

PURPOSE

The purpose of this guideline is to assist the nuclear medicine physician in treating and managing patients who may be candidates for radio-immunotherapy. The guideline also stresses the need for close collaboration with the physician(s) treating the patient for the underlying disease.

Preparation and evaluation of 89Zr-Zevalin for monitoring of 90Y-Zevalin biodistribution with positron emission tomography

PURPOSE

To evaluate whether (89)Zr can be used as a PET surrogate label for quantification of (90)Y-ibritumomab tiuxetan ((90)Y-Zevalin) biodistribution and dosimetry before myeloablative radioimmunotherapy.

METHODS

Zevalin was labelled with (89)Zr by introducing N-succinyldesferal (N-sucDf) as a second chelate. For comparison of the in vitro stability of (89)Zr-Zevalin and (88)Y-Zevalin (as a substitute for (90)Y), samples were incubated in human serum at 37 degrees C up to 6 days. Biodistribution of (89)Zr-Zevalin and (88)Y-Zevalin was assessed at 24, 48, 72 and 144 h p.i. by co-injection in nude mice bearing the non-Hodgkin's lymphoma (NHL) xenograft line Ramos. The clinical performance of (89)Zr-Zevalin-PET was evaluated via a pilot imaging study in a patient with NHL, who had undergone [(18)F]FDG-PET 2 weeks previously.

RESULTS

Modification of Zevalin with N-sucDf resulted in an N-sucDf-to-antibody molar ratio of 0.83+/-0.04. After radiolabelling and purification, the radiochemical purity and immunoreactivity of (89)Zr-Zevalin always exceeded 95% and 80%, respectively. (89)Zr-Zevalin showed the same stability in serum as (88)Y-Zevalin, with a radiochemical purity >95% during a period of 6 days. The co-injected (89)Zr-Zevalin and (88)Y-Zevalin conjugates showed a very similar biodistribution, except for liver and bone accumulation at 72 and 144 h p.i., which was significantly higher for (89)Zr than for (88)Y. PET images obtained after injection of (89)Zr-Zevalin showed clear targeting of all known tumour lesions.

CONCLUSION

(89)Zr-Zevalin and (88)Y-Zevalin showed a very similar biodistribution in mice, implying that (89)Zr-Zevalin-PET might be well suited for prediction of (90)Y-Zevalin biodistribution in a myeloablative setting.

Ibritumomab tiuxetan for non-Hodgkin's lymphoma

Targeted radiation therapy, or radioimmunotherapy, has been an important recent advancement in the treatment of patients with B-cell non-Hodgkin's lymphoma (NHL). 90Y ibritumomab tiuxetan comprises the murine monoclonal antibody ibritumomab, the linker chelator tiuxetan and the radiolabeled isotope 90yttrium. 90Y ibritumomab tiuxetan has been demonstrated to be efficacious in the treatment of B-cell NHL. Initial Phase I/II trials established the therapeutic dose of ibritumomab tiuxetan for low-grade NHL to be 0.4 mCi/kg, or 0.3 mCi/kg for patients with mild thrombocytopenia. Currently, there are many ongoing trials of ibritumomab tiuxetan with different dose schedules and intensities, in combination with chemotherapy and with stem cell transplantation, in an attempt to improve response rate and duration and to study its effectiveness in other B-cell lymphomas, including diffuse large B-cell lymphoma and mantle cell lymphoma. Radioimmunotherapy has great promise and the safe incorporation of 90Y ibritumomab tiuxetan into treatment will hopefully result in improved survival for patients with NHL.

Advances in the treatment for haematological malignancies

Despite the progress made in the last decade in the treatment of haematological malignancies, most of the patients still have a dismal prognosis. However, the improved knowledge of tumour biology opened the possibility to develop new 'intelligent' therapeutic strategies, the so-named targeted therapies. These approaches aim to selectively kill cancer cells by basing this selectivity on both the expression of a specific molecule on their surface or the activation of particular molecular pathways secondary to malignant transformation. In this article, the authors review the main targeted therapies available in haematology, such as monoclonal antibodies, tyrosine kinase, farnesyltransferase, as well as proteasome inhibitors, antiangiogenesis compounds and antisense oligonuceotides. Finally, the authors focus on the application of imatinib mesylate in chronic myeloid leukaemia as the paradigm of molecular treatment. Although these novel therapies are beginning to fulfil their promise, continued research efforts are needed to determine the optimal role of these strategies in haemato-oncology.

Initial evaluation of 227Th-p-benzyl-DOTA-rituximab for low-dose rate α-particle radioimmunotherapy

Radioimmunotherapy has proven clinically effective in patients with non-Hodgkin's lymphoma. Radioimmunotherapy trials have so far been performed with beta-emitting isotopes. In contrast to beta-emitters, the shorter range and high linear energy transfer (LET) of alpha particles allow for more efficient and selective killing of individually targeted tumor cells. However, there are several obstacles to the use of alpha-particle immunotherapy, including problems with chelation chemistry and nontarget tissue toxicity. The alpha-emitting radioimmunoconjugate (227)Th-DOTA-p-benzyl-rituximab is a new potential anti-lymphoma agent that might overcome some of these difficulties. The present study explores the immunoreactivity, in vivo stability and biodistribution, as well as the effect on in vitro cell growth, of this novel radioimmunoconjugate. To evaluate in vivo stability, uptake in balb/c mice of the alpha-particle-emitting nuclide (227)Th alone, the chelated form, (227)Th-p-nitrobenzyl-DOTA and the radioimmunoconjugate (227)Th-DOTA-p-benzyl-rituximab was compared in a range of organs at increasing time points after injection. The immunoreactive fraction of (227)Th-DOTA-p-benzyl-rituximab was 56-65%. During the 28 days after injection of radioimmunoconjugate only, very modest amounts of the (227)Th had detached from DOTA-p-benzyl-rituximab, indicating a relevant stability in vivo. The half-life of (227)Th-DOTA-p-benzyl-rituximab in blood was 7.4 days. Incubation of lymphoma cells with (227)Th-DOTA-p-benzyl-rituximab resulted in a significant antigen-dependent inhibition of cell growth. The data presented here warrant further studies of (227)Th-DOTA-p-benzyl-rituximab.

Radiation therapy for localized low-grade non-Hodgkin's lymphomas

The most common low grade B-cell non-Hodgkin's lymphomas are follicular lymphomas, and extranodal marginal zone lymphomas, also known as mucosa-associated lymphoid tissue (MALT) lymphomas. Localized presentations of follicular lymphoma occur in 20-30% of cases, while for MALT lymphomas, stage I-II disease presentations occur in 70-90%. These are radiation-sensitive lymphomas. Following moderate dose local radiation treatment (30-35 Gy) for these stage I and II low grade lymphomas, the clinical results indicate long-term local control and possible cure. While local control is achieved with minimal morbidity with involved-field radiation therapy, a significant proportion of patients relapse with systemic disease outside of radiation fields. For follicular lymphoma, this occurs in approximately 50% of patients after 15 years, and for non-gastric MALT lymphoma, 30-40% after 10 years. Although patients with relapsed systemic disease are not curable with chemotherapy, the disease often behaves in an indolent fashion and prolonged survival is observed. For gastric MALT lymphomas, radiation therapy is indicated in patients whose lymphoma did not respond to Helicobacter pylori eradication therapy, or in gastric lymphoma not related to this microorganism. The subject of causative agents responsible for non-gastric MALT lymphomas is under active study and the identification of putative microorganisms will lead to improved treatment strategies for these unusual lymphomas, similar to the success in gastric lymphomas over the last decade.