Non-adherence may be defined, for example, as non-perfect adherence (i.e. less than 100%), another cutoff with proven clinical significance, or simply as a numerical value representing the percentage of medication taken, relative to that recommended. This definition, together with the method used to measure adherence, can greatly influence reported rates of non-adherence in any given clinical setting. Taking all these limitations into account, reported rates of non-adherence to oral anti-cancer regimens across empirical studies average approximately 25% 2,3.Accordingly, using pharmacy refill data, a recent retrospective study demonstrated that 33% of newly diagnosed MM patients were non-adherent to lenalidomide treatment (defined as adherence < 80%)4. This is the only study, assessing adherence to lenalidomide in MM patients, which we are aware of.