When do you consider re-treatment with lenalidomide in later line therapy for relapsed multiple myeloma?

It is a challenging question due to the fact all studies post lenalidomide failure even in maintenance never included lenalidomide based therapy in first up to third line of therapy: such as Dara/Pom/dex, Dara/Car/dec, Elo/Pom/dex, Pom/Vel/dex … some argue that since the patient was on low dose of l...