• Efficacy (in order to evaluate the response) of a sequential treatment scheme of Bortezomib in combination with Fludarabine,Cytarabine and Idarubicin continued with Bortezomib monotherapy for patients with relapsed or refractory AML ≥18 years old. [ Time Frame: 1 year ] [ Designated as safety issue: No ]
  

• Evaluate the safety and tolerance of the sequential treatment scheme proposed with Bortezomib combined with Fludarabine, Cytarabine and Idarubicin and in monotherapy, measured on clinical toxicities and laboratory incidences [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
  
• Evaluate the Minimal Residual Disease (MRD)impact that will be monitored by multiparametric flow cytometry carried out at different moments during the treatment [ Time Frame: 1 year ] [ Designated as safety issue: No ]
  

Initially a phase I will be performed to determine the appropriate dose of Cytarabine to be used in Flag-Ida regimen in combination with Velcade; for that reason, first 9 patients will be distributed to 3 different cohorts with 3 patients in each cohort, which will be treated at each Cytarabine dose level (200 mg/m2-500 mg/m2-1000 mg/m2)in combination with the other drugs from Flag scheme and the fixed dose of Velcade at 1,3 mg/m2. Once the appropriate Cytarabine dose is determined,the recruitment will be completed with 40 patients and evaluations and visits program will be realized in three periods: Pre-treatment, Treatment and Follow-up. The Pre-treatment includes Screening and baseline visits. After providing informed consent, patients will be evaluated for study eligibility.

Eligible patients included in the study will receive the first cycle, which consist of Fludarabine, Cytarabine and Idarubicin in combination with 2 times per week of Velcade administration. Each 28-day treatment, patients will be evaluated, and in absence of disease progression or unacceptable toxicity, patients will start second cycle with Bortezomib in monotherapy two times per week followed by a 10 days rest period. That is, patients who response with acceptable toxicity will receive the combined sequential scheme twice (as induction and consolidation).

Patients will be evaluated the day 1 of each cycle,during the treatment period, in order to know the response before carrying on the treatment. Once the Treatment period is completed, patients will be evaluated during the Follow-up period, one monthly visit in year 1, and every 3 months for 3 next years. On each center criteria, autologous/allogeneic transplant can be planned depending on age and HLA identical sibling donor make it possible: it will be done following the sequential scheme (Velcade-Flag-Ida and Velcade in monotherapy); if the patient is not candidate for a transplant or has no donor, he/she will receive 2 sequential scheme. Safety will be evaluated through all adverse events monitoring, physical exploration, vital signs, hematimetric and biochemical analysis. The treatment response will be evaluated using Cheson's standardized criteria, and MRD impact will be necessary evaluated the day 1 of each new cycle before to carry on the treatment.