Grade 3 or 4 neutropenia was significantly more frequent with high-dose melphalan than with MPR ( 94.3 % vs. 51.5 % ) , as were gastrointestinal adverse events ( 18.4 % vs. 0 % ) and infections ( 16.3 % vs. 0.8 % ) ; neutropenia and dermatologic toxic effects were more frequent with lenalidomide maintenance than with no maintenance ( 23.3 % vs. 0 % and 4.3 % vs. 0 % , respectively ) .