• Disease clinical response to treatment - complete response rate. [ Time Frame: Pre-transplantation; post-transplantation (one week following Ybritumomab Tiuxetan (Zevalin) administration); And three months post-transplantation ] [ Designated as safety issue: No ]
  

• Haematopoietic and extra-haematopoietic toxicity of the Ybritumomab Tiuxetan (Zevalin) plus BEAM regimen. [ Time Frame: 36 months ] [ Designated as safety issue: Yes ]
  
• Overall response rate (complete + partial response) [ Time Frame: 36 month ] [ Designated as safety issue: No ]
  
• Progression-free-survival [ Time Frame: 36 month ] [ Designated as safety issue: No ]
  
• Overall survival [ Time Frame: 96 months ] [ Designated as safety issue: No ]
  
• Post-transplantation haematological and immunological reconstitution [ Time Frame: Until post-transplantation day +100 ] [ Designated as safety issue: No ]
  

Inclusion Criteria:

1. Give their written informed consent.

2. Abide by at least one of the following conditions:

   • Obtain no partial response after first-line chemotherapy including anthracyclines + rituximab (R-CHOP, R-MegaCHOP, R-EPOCH or the like), or else
   • Absence of partial response after having received salvage (post-induction) chemotherapy including R-IFE, R-ESHAP, R-ICE or the like.
   • Patients on first recidivation who do not attain partial remission after salvage chemotherapy.
   • Patients with transformed lymphoma, on first partial remission (No CR).
3. Stable disease at the time of transplantation.
4. Age ≥ 18 but ≤ 70.
5. Life expectancy of greater than three months.

Additionally, to be able to undergo haematopoietic stem cell transplantation, all patients should satisfy the requirements of routine clinical practice, i.e.:

1. Performance status (ECOG) < 3.
2. FEV1, DLCO and FVC ≥ 50% of the normal theoretical values.
3. Ventricular ejection fraction (through echocardiography or isotope ventriculography) ≥ 50%.
4. Total bilirubin and transaminases < 3 times the normal maximum value, except if attributable to the underlying disease.
5. Creatinine < 2 times the maximum normal value, and creatinine clearance > 40 ml/min, except if attributable to the underlying disease.
6. Absence of symptomatic heart disease, cirrhosis or active B or C virus hepatitis.
7. HIV negative.

Exclusion Criteria:

1. Impossibility of collecting, via apheresis, a number of CD34+ cells ≥ 2 x 106/kg.
2. Known hypersensitivity to mouse proteins.
3. Involvement of CNS by lymphoma.
4. Progressive lymphoma during the month prior to the date of transplantation.
5. Previous radioimmunotherapy.
6. Previous autologous transplantation of haematopoietic stem cells.
7. Pregnant or breastfeeding women, or adults of childbearing age who are not using an effective contraceptive method.
8. Being submitted to treatment in a clinical trial for 30 days prior to entry in this trial.
9. Active psychiatric disease, including addiction disorders.
10. Existence of active not-haematopoietic neoplasia, with the exception of cutaneous basal carcinoma or cervix intraepithelial carcinoma.