Median progression-free survival was significantly longer with lenalidomide maintenance than with no maintenance ( 41.9 months vs. 21.6 months ; hazard ratio for progression or death , 0.47 ; 95 % CI , 0.33 to 0.65 ; P < 0.001 ) , but 3-year overall survival was not significantly prolonged ( 88.0 % vs. 79.2 % ; hazard ratio for death , 0.64 ; 95 % CI , 0.36 to 1.15 ; P = 0.14 ) .