UPDATE 2-Hologic sterilization device approvable-US advisers

(Recasts with panel vote, new details and background)

By Kim Dixon and Debra Sherman

GAITHERSBURG, Md./CHICAGO, Dec 13 (Reuters) - A U.S. advisory panel said on Thursday that an experimental device made by Hologic Inc (HOLX.O) to permanently sterilize women could be approved if several post-marketing studies are conducted.

The U.S. Food and Drug Administration will have the final say on whether to approve the Adiana system, which uses a catheter to implant a silicone device in the fallopian tubes to prevent pregnancy.

The FDA usually accepts the advice of its advisory panels.

The only current FDA-approved nonsurgical female sterilization procedure is the Essure system made by Conceptus Inc (CPTS.O), which uses a metal coil device implanted in the fallopian tubes.

Both systems work by stimulating scar tissue growth in the fallopian Tubes, effectively blocking the tubes, and preventing sperm from reaching the egg.

Panelists said the Adiana device was generally safe, although a majority had doubts about whether the company's stated "success rate" in preventing pregnancies could be generalized to a broader population.

The panel said a list of conditions, including a new study and following current patients for up to 10 years, would satisfy concerns about effectiveness. It also asked that the device's label note its long-term effectiveness was unknown.

The advisory panel's acting chairwoman, Marcelle Cedars of the University of California, said the 10-3 vote reflected "a desire to give good care for women and to allow women to have more choices."

Some of the experts were troubled that many patients were excluded from the company's effectiveness analysis, which could have skewed the pregnancy rate.

Of 645 women on whom the procedure was attempted, 553 were evaluated for the company's main effectiveness goal. The difference includes those lost to follow up, or excluded for other reasons.

Although six patients became pregnant in the company's clinical trial after one year, the device easily met its goal of a one-year pregnancy rate of less than 5 percent.

The most common adverse events were cramping, vaginal spotting and bleeding, said FDA staff.

"I am just concerned that the rates we are seeing here won't hold up in actual use," said Ralph D'Agostino, a panel member and statistician at the Department of Math and Statistics at Boston University.

Some panel members expressed disappointment at relying on post-marketing studies. Critics of such studies say the FDA has limited authority to ensure their completion.