UPDATE 3-Roche's Actemra successful in arthritis study

* Improves symptoms of sJIA after 12 weeks of therapy

* Meets primary endpoint in Phase III study

* EMA rules against Avastin use for aggressive brain cancer

* Stock up 0.1 pct vs 1.3 pct drop in sector

(Adds EU ruling on Avastin, updates shares)

By Katie Reid

ZURICH, Nov 20 (Reuters) - A treatment which could offer relief for thousands of sufferers of a type of childhood arthritis came a step nearer approval on Friday as Roche (ROG.VX) said its Actemra drug had been successful in a late-stage clinical trial.

The Swiss drugmaker said Actemra, mainly targeted at rheumatoid arthritis, had significantly improved symptoms of onset Juvenile Idiopathic Arthritis (sJIA), a form of the disease that can cause fever, rash and sore joints in children.

The Phase III trial showed patients had fewer disease signs and symptoms after taking Actemra for 12 weeks when compared with those treated only with a placebo, Roche said, adding the study also showed the drug was well tolerated.

However, use of the drug to treat sJIA remains a sideline for Actemra, which is a potential blockbuster, or billion-dollar seller, for Roche in its main application.

Roche has already won approval for Actemra in Japan and Europe, but is still awaiting approval in the United States.

"The results ... confirm earlier data from two Japanese studies and is thus an incremental positive for the drug," said Helvea analysts Karl-Heinz Koch and Odile Rundquist in a note.

"However, with the patient population (for sJIA) limited to 15,000 patients in the developed world the sales potential is small, at less than $200 million," they said.

But the data was likely to boost the efficacy profile of the drug and should enhance chances for approval in the United States, the Helvea analysts said.

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At 1340 GMT, Roche's stock was up 0.1 percent at 161.30 Swiss francs, outperforming a 1.3 percent drop in the European pharmaceuticals sector .SXDP.

There are no treatments yet approved for sJIA, which accounts for almost two-thirds of all deaths among children with arthritis and the overall mortality rate is estimated to be between 2 to 4 percent, Roche said.

The illness can also lead to rapid joint destruction despite aggressive treatment.

Around 70 centres in 20 countries took part in the study.

In October, data from another late-stage clinical trial showed that Actemra significantly halted the progression of joint damage in patients with rheumatoid arthritis for two years when combined with the common treatment methotrexate. [ID:nN16364143]

Separately Europe's drugs watchdog said Roche's blockbuster cancer treatment Avastin should not be used in patients with aggressive brain cancer, going against a recent green light from U.S. regulators.

A committee recommended against extending use of Avastin alone or in combination with irinotecan in patients with glioblastoma, the European Medicines Agency said.

The U.S. Food and Drug Administration approved Avastin, Roche's most important drug which is already used to treat lung, colon and breast cancers, against glioblastoma in May. (Additional reporting by Paul Arnold; Editing by John Stonestreet and David Holmes)