PREVIEW-Glaxo hopes for boost from prostate cancer study

* Data on Avodart in cancer prevention due April 27

* Positive result might add $500 mln to $1 bln to sales

By Ben Hirschler

LONDON, April 14 (Reuters) - GlaxoSmithKline Plc's (GSK.L) big push into cancer treatments has proved slower than initially hoped but the world's second-biggest drugmaker could get a significant boost if a prostate cancer study hits expectations this month.

Results of the four-year, 8,000-patient trial of prostate medicine Avodart will be unveiled at the American Urological Association meeting in Chicago on April 27 and, if successful, could add between $500 million and $1 billion to annual sales, analysts believe.

"Hopefully, we may offer a treatment that will reduce the risk of cancer for men that are considered at risk," Glaxo's head of oncology, Paolo Paoletti, said in a telephone interview.

Avodart, which had sales of 399 million pounds ($588 million) in 2008, is currently approved to treat benign prostate enlargement.

But there is reason from past studies to believe the drug may also prevent cancer, opening up a substantial new market.