Six years after the worst day of her life -- the day her husband, Alan, underwent seven hours of brain surgery to remove a cancerous tumor -- Ellie Marks, of Lafayette, is more determined than ever to warn others of the dangers of cellphones.

Alan, a real estate broker, was forever holding the phone to his right ear -- about an hour a day for 20 years, he guesses -- and she's certain that extended exposure to harmful electromagnetic radiation caused the golf-ball sized growth on the same side of his brain.

Since then, she has testified before Congress, appeared on network telecasts and done countless radio shows to spread the word: Use headsets or speakerphones, hold your phone at a distance, but don't press it to your ear.

She was at it again Thursday night at the Lafayette Library and Learning Center, where about 200 attendees listened to her story and the cautionary words of former Columbia University professor Martin Blank, an expert on physiology, cellular biophysics and electromagnetic fields.

"I'm hearing from people weekly with brain tumors they attribute to cellphone use," Marks said. "The new thing now is young women keeping their phones in their bras -- and they're getting breast cancers."

Marks has repeatedly urged lawmakers to require labels on cellphone packaging -- not warning of health threats but recommending precautions -- only to discover that telecommunications lobbyists are powerful opponents. She said they last year pressured San Francisco supervisors into repealing a labeling law enacted in 2011. Then a similar law in Maine, due for a final reading and perfunctory approval, was defeated after industry lobbyists exerted influence.

"All we're trying to do is get the same information that's hidden in owners manuals displayed at the point of sale," she said. Typical of that is this excerpt from an iPhone 4 users manual: "When using iPhone near your body for voice calls or wireless data information over a network, keep iPhone at least 15 mm (5/8 inch) away from the body ..."

"We keep getting shut down by industry pressure," Marks said. "Now we're just trying to raise awareness through education.

Thursday's forum was sponsored by the California Brain Tumor Association, which Marks and her son, Zack, founded in 2009, and it captivated a packed room. The crowd learned that Federal Communications Commission standards for cellphone emissions have not been updated since 1996 and measure only thermal, not microwave, radiation. It learned the World Health Organization regards mobile phone use as a Class 2B carcinogen, a category that includes DDT, lead, diesel fuel and gasoline.

Blank, who's studied electromagnetic fields for more than 40 years, told listeners the U.S. Department ¿of the Interior recently expressed its grave concerns to the FCC that radiation emitted by cell towers was having negative impacts on the health of migratory birds and other wildlife.

Blank said he regards himself as a teacher, not an activist, and what's happening is less a debate over electromagnetic radiation's impact than a gradual conversion. "It's inevitable," he said. "The facts keep piling up. You find more and more people coming down with cancers and other ailments."

Marks spends most of her waking hours at her cause. She knows the heartache of a brain tumor.

That's why she's doing everything possible to spare others the experience.

Contact Tom Barnidge at tbarnidge@bayareanewsgroup.com