Krista (left) and Emma Stone
05/22/2013 at 01:00 PM EDT
As a kid, Emma Stone
never liked to be separated from her mom for long.
So when Krista Stone
called her daughter in October 2008 to break the news that she'd been diagnosed with triple negative breast cancer, Stone did everything in her power to be there for her.
"I was oddly stoic, the opposite of how I usually am," the actress revealed May 21 at the Triple Negative Breast Cancer Foundation's 6th Annual Peace, Love and a Cure cocktail reception in Creskill, N.J. "But it was terrifying."
At 19, living solo in Los Angeles with her career just starting to take off, Stone still made her mom a priority, flying back home to Arizona as often as possible to be with her through her treatments – including a double mastectomy and a year and a half of grueling chemo.
"I'm sure, in private, Em lived in fear and anxiety," says her mom, who was honored at the reception. "But she really shifted into this [mode of], 'We're going to take care of this, and everything's going to be fine."
About 10 to 20 percent of the 180,000 breast cancers diagnosed each year are considered triple negative, which are highly aggressive and notoriously tough to treat.
Carriers of the BRCA gene mutation (as is carried by
, she herself revealed, Angelina Jolie
) have an 85 percent chance of being triple negative – though Stone's mom "tested for the gene mutation and she was negative, which was very lucky," she says.
Later this year Krista – who got matching blackbird tattoos with the actress after her experience – will celebrate five years cancer-free. Says Stone, "It's incredible."
For more information on triple negative breast cancer and ways you can help, visit Triple Negative Breast Cancer Foundation