An AE that resulted in any of the following outcomes was defined as a serious adverse event (SAE):

• Death;
• Life-threatening event;
• Any inpatient hospitalization or prolongation of existing hospitalization;
• Persistent or significant disability or incapacity;
• Congenital anomaly or birth defect;
• Any other important medical event.

The investigator determined the relationship of an AE to study drug based on the timing of the AE relative to drug administration and whether or not other drugs, therapeutic interventions, or underlying conditions could provide a sufficient explanation for the event.

The severity of an AE was evaluated by the investigator according to National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) (Version 3.0) where Grade 1 = Mild, Grade 2 = Moderate, Grade 3 = Severe, Grade 4 = Life-threatening and Grade 5 = Death.

Safety population: all patients who received at least 1 dose of study drug.

Maximum observed plasma concentration of lenalidomide after a single dose on Day and after multiple doses (Day 4).

Pharmacokinetic (PK) population: all patients who adhered to the study treatment during the course of PK assessment (Days 1 to 5 of Cycle 1) and from whom blood and urine samples were collected.

Time to maximum observed plasma concentration of lenalidomide after a single dose on Day 1 and multiple doses (Day 4).

PK population

Area under the plasma concentration-time curve from time zero to the last measurable concentration (AUCt) of lenalidomide after a single dose on Day 1 and multiple doses (Day 4).

PK population

Area under the plasma concentration-time curve over the dosing interval (AUCτ) of lenalidomide after a single dose on Day 1 and multiple doses (Day 4).

PK population with available data

Area under the plasma concentration-time curve from time zero to infinity (AUC∞) of lenalidomide after a single dose on Day 1.

PK population with available data

The apparent terminal half-life is the time required for plasma concentration to decrease by 50% after pseudo-equilibrium of distribution has been reached, and calculated as the natural logarithm of 2 (0.693) / Apparent terminal rate constant (λz).

PK population with available data

Apparent volume of distribution of lenalidomide after a single dose on Day 1 and multiple doses (Day 4).

PK population with available data

Apparent total plasma clearance (CL/F) of lenalidomide after a single dose on Day 1 and multiple doses (Day 4).

PK population with available data

Apparent terminal elimination rate constant of lenalidomide determined after a single dose on Day 1 and multiple doses (Day 4).

PK population with available data

Erythroid response was determined using the International Working Group (IWG) 2000 criteria, categorized as a major response or minor response.

A major response in patients with transfusion-dependent anemia (receiving ≥ 4.5 units of red blood cell (RBC) transfusion during 56 consecutive days at Baseline) is defined as RBC transfusion independence accompanied by a ≥1.0 g/dL increase from Baseline in hemoglobin sustained for 56 days consecutively during the treatment period. In patients with transfusion-independent anemia with hemoglobin < 10 g/dL at Baseline a major response is defined as a > 2.0 g/dL increase from Baseline in hemoglobin sustained for consecutive 56 days.

Minor response in patients with transfusion-dependent anemia defined as ≥ 50% decrease from Baseline in transfusion requirements sustained for consecutive 56 days, and in transfusion-independent patients as 1.0 to 2.0 g/dL increase from Baseline in hemoglobin sustained for consecutive 56 days.

Efficacy population: all patients who had a diagnosis of low- or intermediate-1-risk MDS associated with anemia based on confirmation by the central reviewers and received at least 1 dose of study drug.

Time to erythroid response was calculated as the time from the first dose of study drug to the start of the first major or minor erythroid response. Similarly, time to major erythroid response was calculated as the time from the first dose of study drug to the start of the first major erythroid response.

Efficacy population

Duration of erythroid response was calculated as the time from the start of the first major or minor erythroid response to the end of the response. Similarly, duration of major erythroid response was calculated as the time from the start of the first major erythroid response to the end of the response. Response duration was censored at the last adequate assessment for patients who maintained response.

Efficacy population with a erythroid response

Change in hemoglobin concentration from Baseline to the maximum observed value during the major erythroid response period for major erythroid responders.

Efficacy population with a erythroid response

Neutrophil response was determined using the IWG (2000) criteria. A major response for participants with a Baseline neutrophil count < 1,500/mm^3 is defined as a ≥ 100% increase or a ≥ 500/mm^3 increase, whichever is greater, sustained for consecutive 56 days during the treatment period.

A minor response for participants with a Baseline neutrophil count < 1,500/mm^3 is defined as a ≥ 100% increase, but an absolute increase < 500/mm^3, sustained for consecutive 56 days during the treatment period.

Efficacy population with Baseline neutrophil count < 1,500/mm^3.

Platelet response was determined using the IWG (2000) criteria. Major response in patients with Baseline platelet count < 100,000/mm^3 is defined as a ≥ 30,000/mm^3 increase sustained for consecutive 56 days during the treatment period. In platelet-transfusion-dependent patients at Baseline a major response is defined as stabilization of platelet counts and platelet transfusion independence sustained for consecutive 56 days during the treatment period.

Minor response in patients with Baseline platelet count < 100,000/mm^3 is defined as a ≥ 50% increase in platelet count with an absolute increase > 10,000/mm^3 and < 30,000/mm^3 sustained for consecutive 56 days during the treatment period.

Efficacy population with a Baseline platelet count of < 100,000/mm^3 or who were platelet-transfusion dependent at Baseline. There were no patients with platelet count of < 100,000/mm3 or who were platelet-transfusion dependent at Baseline, and thus platelet response was not evaluated.

Cytogenetic (chromosome structure) abnormalities were assessed by a central cytogenetic reviewer based on prints and cytogenetic reports of the bone marrow sample from the central laboratory. Cytogenetic response was determined using the IWG (2000) criteria and categorized as either a major response or minor response. Twenty metaphases were analyzed for the determination of cytogenetic response.

A major response was defined as no detectable cytogenetic abnormality, if an abnormality was present at Baseline, sustained for consecutive 56 days during the treatment period. A minor response was defined as ≥ 50% reduction from Baseline in abnormal metaphases sustained for consecutive 56 days during the treatment period.

Efficacy population

Bone marrow morphology was assessed by the central hematologic reviewers based on the locally-prepared bone marrow smear slide and clot section.

Efficacy population with available bone marrow specimens.

Bone marrow morphology was assessed by the central hematologic reviewers based on the locally-prepared bone marrow smear slide and clot section.

Efficacy population with available bone marrow specimens at each time point (indicated by "N").

Bone marrow morphology was assessed by the central hematologic reviewers based on the locally-prepared bone marrow smear slide and clot section.

Efficacy population with available bone marrow specimens at each time point (indicated by "N").