Sept 28 (Reuters) - Roche said on Monday its experimental drug ocrelizumab had proved effective against primary progressive multiple sclerosis in a keenly awaited final-stage clinical trial.

The injectable antibody medicine is the first product to show positive study results in both the hard-to-treat progressive form of the disease and more common relapsing forms, underscoring its multibillion-dollar sales potential.

(Reporting by Ben Hirschler, editing by Louise Heavens)