VIENNA (Reuters) - Swiss drugmaker Roche said on Sunday its rheumatoid arthritis medication Actemra for giant cell arteritis showed to be superior to steroids alone in maintaining steroid-free remission in a Phase III study.

Results from the study showed that 56 percent of patients treated with Actemra - known as RoActemra in European markets -achieved steroid-free disease remission at one year, versus 14 percent with a six-month steroid only taper regimen, Roche said in a statement.

Giant cell arteritis (GCA) is a chronic, potentially life-threatening autoimmune condition caused by inflammation of large and medium-sized arteries, most often in the head but also in the aorta and its branches. It generally affects people over the age of 50.

"Treatment to date for GCA has been limited to high-dose steroids to rapidly control inflammation and prevent serious complications such as vision loss," said Sandra Horning, Chief Medical Officer and Head of Global Product Development.

However, steroid treatment often failed to control disease in the long term and could be associated with severe side effects, she said.

"If approved, Actemra could have the potential to fundamentally change the way people with GCA are treated."

Actemra is Roche's fifth-best-selling medicine, with first-half 2016 sales rising 17 percent to 814 million Swiss francs as doctors prescribed it for rheumatoid arthritis and juvenile idiopathic arthritis.

The U.S. Food and Drug Administration had granted breakthrough status to Actemra's rheumatoid arthritis medication for giant cell arteritis in October.

The study results will be submitted to regulatory authorities around the world by end of 2016, Roche said.

(Reporting by Kirsti Knolle; Editing by Elaine Hardcastle)