Cancer drug discovery by repurposing: teaching new tricks to old dogs.

Highlights: [•] Drug repurposing is the process of developing new indications for approved and abandoned drugs. [•] Approximately 90% of approved drugs possess secondary indications. [•] Cancer drug development through repurposing has less risk of failure. [•] Only a few non-cancer drugs (e.g., thalidomide) have progressed straight to cancer patients. [•] The hurdles associated with expensive Phase II and III clinical trials have not changed over the years. [Copyright &y& Elsevier]