Treatment strategies in relapsed and refractory multiple myeloma: a focus on drug sequencing and 'retreatment' approaches in the era of novel agents.

Treatment of multiple myeloma has evolved over the last decade, most notably with the introduction of highly effective novel agents. It is now possible to aim for deep disease responses in a greater number of patients in an attempt to prolong remission duration and survival. Initially introduced in the relapsed setting, the novel agents, namely thalidomide, bortezomib and lenalidomide, are now being increasingly incorporated into upfront treatment strategies, raising questions about the feasibility of 'retreatment' with such agents. Also, in a disease that is characterized by multiple relapses, the 'sequencing' of the different effective options is an important question. In the frontline setting, the first remission is likely to be the period during which patients will enjoy the best quality of life. Thus, the goal should be to achieve a first remission that is the longest possible by using the most effective treatment upfront. At relapse, the challenge is to select the optimal treatment for each patient while balancing efficacy and toxicity. The decision will depend on both disease- and patient-related factors. This review aimed to assess the available research data addressing 'retreatment' approaches, drug 'sequencing' and the long-term impact of upfront therapy with novel drugs.