Swiss pharmaceutical giant Roche has received the green light from the U.S. Food and Drug Adminstration (FDA) to sell Gazyva (obinutuzumab), its new agent to treat chronic lymphocytic leukemia (CLL) in combination with the chemotherapeutic agent chlorambucil.

Peak sales of the potential blockbuster drug are estimated at at least $1 billion, annually, with some estimates higher. Approval by EU authorities is expected for Q3 2014.

Gazyva is the first treatment approved under the FDA's Breakthrough Therapy program, and approval was given earlier than most observers assumed. The agency had been expected to report in mid-December. Roche said that when combined with chemotherapy, the new drug demonstrated an 84% reduction in the risk of disease worsening or death, compared to chemotherapy alone.

The monoclonal antibody discovered by Roche Glycart, a wholly owned, independent research unit of Roche based near Zurich, Switzerland, is designed to attach to CD20, a protein found only on B-cells. It attacks targeted cells both directly and together with the body's immune system, and some reports said it has been shown to be more efficacious than its predecessor Rituxan (rituximab), whose patent is set to expire.

Gazyva will be jointly marketed in the US by Roche-owned Genentech and Biogen Idec. Roche scientists are also exploring the use of Gazyva in other cancers such as non-Hodgkins lymphoma.