Roche Holding AG (ROG.VX) is confident that breast cancer drug Herceptin still has potential to expand sales more, Peter Brown, life cycle leader for the breast cancer drug said Wednesday.

Herceptin, which already has a market penetration of around 95% in most Western markets, still has potential for sales to expand. But the bigger growth rates in coming years will be posted in emerging markets, Brown added.

He was talking to reporters on a conference call to detail findings of a study released earlier Wednesday, which had demonstrated that women still benefited from having taken Herceptin, four years after the treatment.

Herceptin had sales of 5.1 billion Swiss francs ($4.41 billion) in 2008. The drug is sold in the U.S. by Genentech Inc. (DNA), which developed the drug, and is currently the target of a hostile bid by Roche to acquire the 44% of the U.S. biotechnology company that it doesn't already own.

Asked about competition from GlaxoSmithKline PLC's (GSK) drug Tyverb, Brown said that the dominance of Herceptin is presenting "quite a high hurdle."

In the markets, where Tyverb - also known as Tykerb - has already been launched, market penetration remains low. So far, it looks like GSK "over-promised, and under-delivered" as far Tyverb is concerned, he said.

Tyverb was launched in 2008.

Company Web site: www.roche.com

-By Anita Greil, Dow Jones Newswires; +41 43 443 8044 ; anita.greil@dowjones.com