Treatment for Myelodysplastic Syndromes
Lenalidomide administration is limited by dose-limiting neutropenia and thrombocytopenia.[Level of evidence: 3iiiDiv] Treatment-related thrombocytopenia also correlated with cytogenetic responses, emphasizing the importance of successful suppression of the del(5q) clone with lenalidomide to achieve meaningful responses.
A subsequent phase III study randomly assigned lower-risk del(5q) MDS patients to receive placebo and lenalidomide at either 5 mg daily for 28 days or 10 mg daily for 21 days of a 28-day cycle. Transfusion independence responses lasting longer than 6 months occurred in 43% to 52% of subjects treated on the lenalidomide arms, compared with 6% of controls. The cytogenetic response rate was 25% to 50% on the active treatment arms, and the 3-year risk of AML transformation was 25%.
Lenalidomide has limited activity in lower-risk, red blood cell transfusion–dependent MDS patients who do not harbor the del(5q) lesion. In a phase II study similar in design to the registration study, 56 of 215 patients (26%) achieved transfusion independence. Median duration of response was 41 weeks (range, 8–136 weeks). Grade 3 or 4 myelosuppression occurred in only 20% to 25% of patients, and unlike for del(5q) patients, was not associated with subsequent attainment of a transfusion independence response to therapy.
Antithymocyte globulin (ATG) has shown activity in MDS patients in several small series. The National Heart, Lung, and Blood Institute conducted a phase II trial including 25 MDS patients with less than 20% blasts. Of all the patients studied, 11 (or 44%) responded and became transfusion-independent after ATG (three complete responses, six partial responses, and two minimal responses). Multivariate analysis identified HLA-DR-15 (phenotype) expression, briefer period of red cell transfusion dependence, and younger age as predictors of response to ATG. One study used alemtuzumab to treat a heavily preselected population of lower-risk MDS patients, in whom the response rate was 80%.
DNA methyltransferase inhibitors
The nucleoside 5-azacitidine and decitabine are inhibitors of DNA methyltransferase. Both drugs require prolonged administration before benefits are seen. The median number of cycles required to see first hematologic response to 5-azacitidine was 3; 90% of responders showed response by 6 cycles; and the median number of cycles of decitabine required to see first response was 2.2. Azacitidine received FDA approval based on the results of a randomized trial that was not designed to study survival.