Radioimmunotherapy in follicular lymphomas, a retrospective analysis of the Polish Lymphoma Research Group's (PLRG) experience

Ibritumomab is an 90Yttrium (90Y) labelled radioimmunoconjugate registered to treat follicular lymphoma relapsing or refractory after Rituximab therapy. Combining the specificity of anti CD20 monoclonal antibodies with the efficacy of radiotherapy, it is particularly effective in patients with advanced stages of disease with generalized lymphadenopathy. Twenty-one patients with follicular lymphoma, after failing 2-5 lines of previous treatment, were subjected to radioimmunotherapy in three Polish Lymphoma Research Group (PLRG) centres. Ibritumomab infusion was followed by 2 doses of Rituximab (250 mg/m2 at day -7 and 0) to enhance its biodistribution. Radioimmuno-conjugate was prepared in the Nuclear Medicine Departments of participating centres based on patient weight and full blood count results (14.8 MBq/kg, max 1200 MBq, reduced to 11.1 MBq/kg in cases with blood platelet 100 000-150 000 or leukocytes 1500-2000). 14.8 MBq/kg (0.4 mCi/kg) 100 thousand to 149 thousand/mm3 platelets 11.1 MBq/kg (0.3 mCi/kg). The primary endpoint of the study was the assessment of response rate and haematological toxicity. Objective responses were observed in all patients, with 10 partial and 12 complete regressions. Cytopenia, starting 3-4 weeks after radioimmunotherapy, reflected haematological toxicity - the only important side effect. Thrombocytopenia was more pronounced, with platelet counts of < 50,000/ul in every second patient. One patient developed myelodysplastic syndrome 21 months after the procedure. After the medium time of follow up over 2 years, 2 patients died. Median progression free survival (secondary study endpoint) was 15 months. Ibritumomab radioimmunotherapy is an efficient method of palliation treatment of heavily pre-treated follicular lymphoma patients, failing numerous previous treatment lines. Earlier application increases the number of complete responses and prolongs progression free survival. (author)