 This study is a randomized, double-blind Phase 1 study of FluMist vs. placebo in mild to moderately immunocompromised children 5 to 17 years of age with cancer. The primary objective of this study is to describe the safety of FluMist compared with placebo in mild to moderately immunocompromised children with cancer. The secondary objectives of this study are to describe the immune responses following vaccination with FluMist and to determine the incidence and duration of viral replication following vaccination with FluMist. 