Since ISTs are small proper Phase 2 trials are required
This is true for on-label marketing, but ISTs can be quite convincing, especially when conducted in populations with no or weak alternatives. (If you're looking at a bone marrow transplant or Interleukin-2, Iclusig is a nice option.)
If sufficiently focused and publicised, these can create significant off-label markets.
Granted, label expansion is preferable, but we could see material sales from ISTs. Did someone say "Glioblastoma"?