By John Miller

BASEL, Switzerland (Reuters) - The U.S. Congress may intervene on how much companies can charge for some drugs following a move last year by Turing Pharmaceuticals to ratchet up the price of a treatment for deadly parasite infections by 5,000 percent, Roche's head of pharmaceuticals said.

Roche's Dan O'Day is convinced the oncology portfolio at the world's biggest maker of cancer drugs will not be affected, arguing it offers innovative treatments for diseases with few other options.

O'Day acknowledged Turing's price hike for Daraprim had galvanized U.S. public concern as well as political will to tackle drugmakers who are perceived as abusing pricing power to gouge patients.

"It's really a misuse of the system," O'Day said. "And there very well may be some legislation that stops that from happening."

Democratic presidential candidates Hillary Clinton and Bernie Sanders have been campaigning on the issue.

U.S. prices for the world's 20 top-selling medicines are, on average, three times higher than in Britain, according to an analysis carried out for Reuters for last year.

Novartis Chief Executive Officer Joe Jimenez, whose company includes the Sandoz generics unit, said on Wednesday he expects the U.S. pricing environment to grow "more difficult".

However, O'Day sees no "short term" U.S. pricing pressure for Roche's cancer drugs.

The largest U.S. pharmacy benefit manager, Express Scripts Holding, has said that it has its eye on cancer drug pricing, where treatments can cost more than $100,000 a year.

O'Day sees a gulf opening in the drug world.

"There will be a bifurcation of the industry," he said. "There will be true innovators that are providing transformational medicines. And then there will be the generic medicines. The excitement you've seen has been around generics, certain kinds of companies coming in and massively raising the price."

(Additional reporting by Caroline Humer in New York; Editing by Keith Weir)