Salvage in Patients With Myelodysplastic Syndrome After Failure of Hypomethylating Agents: Lenalidomide as a Second-line Therapy

There is no standard therapy after the failure of hypomethylating agents only providing supportive cares including transfusion or cytokine therapies. Lenalidomide is the treatment of choice in case of MDS with 5q deletion. A study of lenalidomide for non-5q deletion MDS patients showed that transfusion independency rate was 26% which was relatively acceptable and suggested that lenalidomide could be used for non-5q deletion MDS patients. There is no datum for second-line lenalidomide therapy after hypomethylating agents. MDS which has highly complex pathogenesis backgrounds will have distinctive subtype for each therapy and each treatment drug can have distinctive subgroup for the response. In fact the investigators don't know which patient will be responsive hypomethylating agents or lenalidomide except for 5q deletion. This suggests that second line therapy after the first line failure in MDS will be different with other type of relapsed/refractory disease which will be tend to more resistant to subsequent therapies. In this regard, there is a possibility to have a relatively high response rate to second line lenalidomide in this selected subset who has failed to the hypomethylation therapy or some patients will be responsive regardless of treatment line. Recent data suggested that MDS with JAK2 mutation will be responsive to lenalidomide. The investigators will analyze the JAK2 mutation status in response evaluation.