Warren has requested that the United States Patent and Trademark Office investigate Keytruda from Merck.

Senator Elizabeth Warren of the United States recently wrote to the head of the United States Patent and Trademark Office to express her concern that continued efforts to patent Merck & Co.'s (MRK.N) blockbuster cancer treatment Keytruda may constitute an abuse of the patent system.

In a letter sent on Wednesday and seen by Reuters, Warren argued to Kathi Vidal, director of the United States Patent and Trademark Office (PTO),....