This registry is a prospective, non-interventional, post authorisation safety study for patients diagnosed with Transfusion Dependent, IPSS low or intermediate-1-Risk Myelodysplastic Syndrome (MDS), associated to a single abnormality of the chromosome 5 [del(5q)].

The purpose of this study is to collect additional data about the safety of an oral drug (lenalidomide, Revlimid®) that may have been prescribed to relieve anemia and decrease the need of blood transfusions. However, also patients affected by the MDS del(5q) who receive other treatments different from lenalidomide can be included in this study, if they agree.

Inclusion Criteria:

• Are ≥ 18 years old at the time of signing the Informed consent form (ICF)
• Are transfusion dependent or have an history of transfusion dependence; for the purpose of the current Myelodysplastic syndromes (MDS) Post-authorization safety study (PASS), transfusion-dependence is defined as requiring ≥2 RBC units over an 8 week period prior to the date of signature on the ICF (due to MDS-related causes and not because of hemorrhage, trauma, or other acute cause)
• Are on active treatment with lenalidomide (Lenalidomide Cohort) or have never been exposed to lenalidomide at the time of signing the ICF (Background Cohort)
• Have confirmed diagnosis of IPSS low or intermediate-1-risk MDS with isolated del (5q) (with morphological and cytogenetic information) diagnosed on 15 June 2007 (date of Revlimid first approved in Europe) or later

Exclusion Criteria:

• Refuse to participate in the Myelodysplastic syndromes (MDS) Post-authorization safety study (PASS),
• Are currently participating in an interventional therapeutic clinical trial for MDS (except for erythropoiesis-stimulating agents [ESAs] and granulocyte colonystimulating growth factors)
• Receive any investigational agent the time of signing the ICF
• Have previously been treated with lenalidomide and are no longer on active treatment with lenalidomide at the time of signing the ICF

Patients who have received at least 1 dose of any treatment or treatment modality after the patient signs the informed consent form

• Lenalidomide cohort: All patients treated with lenalidomide
• Background cohort: All patients treated with therapeutic modalities other than lenalidomide

For each population 3 datasets will be described and will form the basis of subsequent analyses:

• A baseline demographic dataset ("population dataset")
• An exposure dataset
• An outcome dataset