When it comes to cancer, getting the brush-off from your doctor can be deadly, Dr. Thaïs Aliabadi, an OB/GYN and cohost of the SHE MD podcast, stressed Tuesday during Fortune’s Brainstorm Health conference in Dana Point, Calif.

“Women in general get dismissed when they go to the physician,” Aliabadi said. “Our complaints are dismissed and every time we open our mouths, they tell us we’re exaggerating our symptoms, it’s PMS (premenstrual syndrome), it’s anxiety. So that’s the starting point of a woman going to a physician.”

Aliabadi was diagnosed with breast cancer in 2019 at age 49—despite having no genetic mutations and no family history of the disease. In addition, all of her imaging had been benign. She previously told Fortune she’d used a breast cancer risk assessment calculator to determine that her lifetime risk of developing the disease was 37%. By comparison, the American Cancer Society puts a woman’s average risk at 13%.

Aliabadi opted for a prophylactic double mastectomy, a procedure she said her own doctors had told her was unnecessary. But a week after the surgery, she learned cancer had been present.

“If I told you this plane had a 12.5% chance of crashing, would you board it?” she asked the Brainstorm Health audience. “But when you tell a woman that [they] have a 12.5% chance of getting breast cancer, they’re like, ‘It’s not a big deal, I don’t have it in my family.’ Even if you don’t have it in your family, you start at 12.5%.”

A number of other factors, such as being overweight or having dense breasts, increase a woman’s breast cancer risk.

“If [your risk] is 20% or above, that means you fall into the high-risk category and you have to start your imaging as early as 30, not 40,” Aliabadi said. “And you have to add MRI to it, which is exactly what I did for myself and Olivia Munn.”

Yes, that Olivia Munn, the 43-year-old actress who revealed her own breast cancer diagnosis in March. Munn, who said in an Instagram post that Aliabadi “saved my life,” had a medical history that closely mirrored that of her OB/GYN: a clean mammogram and no genetic mutations, yet a lifetime risk of 37%. Further imaging led to a biopsy, which revealed cancer. Munn, too, had a double mastectomy.

“All [Munn’s] friends were telling her, ‘Why is your doctor so paranoid?’” Aliabadi said. “With my ‘paranoia,’ she had three cancer lesions on her right and one on her left breast.”

Erika Fry, a senior writer at Fortune, moderated the panel on young people getting cancer, which featured Aliabadi; Dr. Kimmie Ng, associate chief of the Division of Gastrointestinal Oncology at the Dana-Farber Cancer Institute; and Dr. Edward Kim, physician-in-chief at City of Hope Orange County.

“This is a really concerning pattern…this is the epidemic that is smoldering underneath us,” Kim said of people under 50 being diagnosed with cancer. “We are not noticing it enough and now it’s becoming apparent. When you walk through our clinics now, you will see people in their forties and their thirties showing up with new cancer diagnoses.”

Ng added, referring to colorectal cancer, “We do think it’s probably some combination of environmental exposures that is causing this uptick, but we don’t know exactly which ones.”

For more on cancer screening:

• The doctor who caught actress Olivia Munn’s breast cancer also diagnosed her own: ‘I don’t want another woman to go through what I went through’
• A 5-minute test can estimate your odds of developing breast cancer—but not if you’re biracial
• Virtual colonoscopy lets you skip the scope. Here’s what to know about the colorectal cancer screening Mark Cuban says saves time and money
• Katie Couric says too many people think colorectal cancer is a man’s disease. She’s imploring women to get potential lifesaving screenings