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

Herceptin, which already has a market penetration of around 75% in most Western markets, has potential for sales to expand, but the bigger growth rates in coming years will be posted in emerging markets, Braun 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 it doesn't already own.

Asked about competition from GlaxoSmithKline PLC's (GSK) drug Tyverb, Braun said the dominance of Herceptin presents "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.

GlaxoSmithKline spokesman Stephen Rea said it's still early days for Tyverb, which was launched in the U.S. in 2007 and in the European Union last year. GlaxoSmithKline believes its use will increase over time as more data become available, he added.

The drug generated GBP102 million in sales last year.

Company Web site: www.roche.com

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

(Elena Berton in London contributed to this item.)