Participants who were receiving vandetanib as randomized treatment will be allowed, upon re-consent, to continue on open-label vandetanib if in the opinion of the Investigator the participant is still receiving benefit. Placebo participants who experience disease progression within 60 days of unblinding may be offered the option of treatment with open-label vandetanib if, in the Investigator's opinion, such treatment may be of clinical benefit to the participant. Approximately 2 years; duration will vary depending on individual participant response.