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The FDA has been amenable to surrogate endpoints for the approval of novel agents in acute lymphoblastic leukemia (ALL), but hard-set guidance remains vague. In 2012 the FDA granted accelerated approval for vincristine sulfate liposome injection (Marqibo) for the treatment of adult patients with Philadelphia chromosome-negative ALL. This approval was based on the rate of complete remission plus the rate of complete remission with incomplete blood count recovery in a single-arm, single-agent trial of 65 adults in second or greater relapse.
The use of surrogate endpoints, such as getting to transplant in a minimal residual disease setting, remain unclear for accelerated approval of treatments for patients with ALL. At this point, the FDA has not provided clear guidance. As a result, a definitive approval still requires the demonstration of prolonged survival.