* Roche trial favours status quo, French trial inconclusive
* Experts say key message is one year of Herceptin is best
* Results limit downside risk for Roche's Herceptin revenues
(Adds more detail, Roche comment on French study, analyst, updates shares)
By Kate Kelland
LONDON, Oct 1 (Reuters) - The results of two studies into Roche's breast cancer drug Herceptin published on Monday showed that the current standard treatment of taking the drug for a year provides the best outcome for patients.
This removes a downside risk for Roche that could have cost the Swiss company up to $1.5 billion in sales if the trials had showed that a shorter treatment of six months would be just as effective.
But the results also limit Roche's ability to squeeze more value out of the lucrative drug before it loses its patent from 2014 because one study showed that extending the time patients take the drug to two years from one was not worthwhile.
Analysts viewed this confirmation of the status quo for treatment with Herceptin as positive for Roche.
Analysts at Chevreux's pharma team in London said the overall picture from the studies was "reassuring for the Herceptin franchise." Shares in Roche were trading up 1.4 percent at 178.4 francs by 1047 GMT.
Analysts had said the Swiss firm, the world's biggest maker of cancer drugs, could lose up to $1.5 billion in revenue from the blockbuster medicine in the medium term if six months treatment had been shown to be just as beneficial.
Herceptin, known generically as trastuzumab, was first approved in 1998 and had 2011 sales of 5.25 billion Swiss francs ($5.5 billion). It is used as a treatment for around a quarter of breast cancer patients who have tumours that generate a protein called HER2, which tends to make their disease more aggressive.
Roche conducted a study that investigated the benefit of using Herceptin for two years rather than one, while an opposing French study looked whether patients got the same benefit from just six months.
The Roche study found no difference in the rate at which patients' cancer recurred or in how long patients lived. The French study's results were inconclusive. Data from both trials were presented at the European Society of Medical Oncology (ESMO) conference in Vienna on Monday.
"The key message for 2012 is that one year of treatment with trastuzumab remains the standard of care for HER2 positive early breast cancer patients," said Richard Gelber, a professor at Harvard Medical School and Dana-Farber Cancer Institute in Boston in the United States, who led the Roche trial.
NO BLACK AND WHITE ANSWER
Presenting the French study, Xavier Pivot of the University de Franche Comte in France, said the results were "inconclusive" but showed a "trend in favour of 12 months treatment" rather than six months.
He said his team was carrying out deeper analysis of the data and would present more results in December, but added:
"The results probably won't give a black and white answer and the researchers will probably need to look at subsets of patients to see who benefits from six months of treatment and who should get a full year."
Roche noted in a statement that Pivot's study also showed that women treated for six months had a 28 percent greater risk of their cancer coming back than those treated for a year.
This finding underlined the benefit of one year Herceptin as standard of care, it said.
The firm's head of global product development Hal Barron said the Roche study results answered an important question "and support current medical practice".
Martine Piccart, who chairs the Breast International Group which carried out the Roche trial, added in a statement:
"It's essential that our clinical trials help us understand just how long patients need to receive a particular treatment.
"These results give us both the evidence and the reassurance that it's not necessary to give patients with early-stage HER2 positive breast cancer Herceptin for more than one year."
The Swiss drugmaker is also due to present new data on Monday on its experimental "armed antibody" drug known as TDM-1 as a treatment for HER-2 positive breast cancer.
TDM-1 combines Herceptin with a derivative of a powerful type of chemotherapy and is designed to reduce the unpleasant side effects of cancer treatments.
(Editing by James Jukwey and Jane Merriman)
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Keywords: ROCHE HERCEPTIN/