To evaluate the use of ibritumomab tiuxetan (Zevalin) as part of the non myeloablative conditioning with melphalan, fludarabine and thiotepa in patients submitted to allogeneic transplantation of haematopoietic stem cells from family donor's peripheral blood.

Inclusion Criteria:

1. Written informed consent

2. Histologically confirmed B-cell lymphoma of the following subtypes:

   • LBCDL
   • Grade 3b follicular lymphoma
   • Mantle-cell lymphoma
   • Transformed B-cell lymphoma
   • Burkitt lymphoma in patients not eligible for a conventional allogeneic transplant

3. High-risk B-cell CD20+ lymphoma defined by

   • Having attained less than PR after two chemotherapy lines
   • Post-transplantation relapse
   • Presence of disease detected through a metabolic approach (PET/CT or else CT+PET) either before or after autologous transplantation
   • Inability to collect enough stem cells for autologous transplantation

4. Stable disease at the time of transplantation

5. Age between 18 and 65

6. Performance status (ECOG) ≤ 2

7. Normal and suitable pulmonary function (DLCO ≥ 30%)

8. Left ventricular ejection fraction (LVEF) determined by ventriculography or echocardiogram ≥ 40%

9. Normal hepatic and renal function, with creatinine ≤ 2 mg/dl and Bi ≤ 1.5 mg/dl, and alkaline phosphatase ≤ 2.5 x UNL ; AST, ALT ≤ 2.5 x UNL (≤ 5 x UNL if hepatic infiltration)

Exclusion Criteria:

1. Prior treatment with radiopharmaceutical agents
2. HIV-associated lymphoma
3. Presence of human anti-mouse antibodies (HAMA) or anti-chimeric antibodies (HACA)
4. Patient's inability to follow the protocol
5. Hypersensitivity to 90Y-itritumomab tiuxetan
6. Presence of severe pathologies that preclude chemotherapeutic treatment
7. Pregnant women or pregnancy risk due to inappropriate contraceptive measures
8. Breastfeeding women