The median progression-free survival was 25.5 months with continuous lenalidomide-dexamethasone , 20.7 months with 18 cycles of lenalidomide-dexamethasone , and 21.2 months with MPT ( hazard ratio for the risk of progression or death , 0.72 for continuous lenalidomide-dexamethasone vs. MPT and 0.70 for continuous lenalidomide-dexamethasone vs. 18 cycles of lenalidomide-dexamethasone ; P < 0.001 for both comparisons ) .