FDAnews
www.fdanews.com/articles/156710-fda-details-reasons-for-breakthrough-therapy-designation-denials

FDA Details Reasons for Breakthrough Therapy Designation Denials

June 28, 2013
The FDA offered some hints last week about why it has denied a third of drugmakers’ breakthrough therapy designation requests, with premature clinical data being the primary culprit. Since creating the designation last year, the FDA has received 64 applications, denied 21 of those and approved the same number.
Drug Industry Daily