[Background]: In two randomized phase III trials (MM-009 and MM-010), lenalidomide plus dexamethasone significantly prolonged time to progression and overall survival (OS) in patients with relapsed/refractory multiple myeloma compared with dexamethasone alone. In both trials the treatment was continued until disease progression or unacceptable toxicity. We conducted a subanalysis to determine if continuing therapy after achieving partial response (PR) improved survival. [Patients and Methods]: Data were collected on 212 patients who were treated with lenalidomide plus dexamethasone and achieved >= PR. Kaplan-Meier survival estimates were compared between patients on continued treatment versus patients discontinuing therapy because of adverse events, withdrawal of consent, or other reasons. Time-dependent multivariate regression analyses were used to determine the benefit of continuing treatment with lenalidomide. [Results]: A total of 174 patients received continued treatment until disease progression or death, and 38 patients discontinued therapy without progression. There was a trend toward longer median OS in patients who continued therapy (50.9 months vs. 35.0 months; P = .0594). When controlling for the number of previous antimyeloma therapies, beta(2)-microglobulin levels, and Dune-Salmon stage (which adversely affected survival in these patients), continued lenalidomide treatment (HR, 0.137; 95% CI, 0.045-0.417; P = .0005) or each additional cycle of lenalidomide (HR, 0.921; 95% CI, 0.886-0.957; P < .0001) were both associated with longer survival. [Conclusion]: Continued lenalidomide treatment until disease progression after achievement of PR is associated with a significant survival advantage when controlling for patient characteristics. These findings should be confirmed in a prospectively designed trial.

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