EXCLUSIVE: Olivia Munn’s doctor details her breast cancer diagnosis and treatment

Olivia Munn revealed she was diagnosed with breast cancer in an Instagram post she shared on March 13.

The post includes a series of photos and videos of Munn, 43, in the hospital and a letter she wrote describing how she came to be diagnosed.

“I hope by sharing this it will help others find comfort, inspiration and support on their own journey,” the actor wrote in her caption.

In the letter, Munn explained she was diagnosed in April 2023 after undergoing a course of genetic tests. While she tested negative for the BRCA gene, a mutation commonly linked to breast cancer, and had a clear mammogram, Munn’s OB-GYN calculated her breast cancer risk assessment score and determined she had a 37% lifetime risk of having breast cancer.

So, Munn underwent an MRI, an ultrasound and a biopsy. “Two months later I was diagnosed with breast cancer,” she wrote.

What is luminal B cancer?

Munn said she has luminal B cancer in both breasts, which she described as “an aggressive, fast moving cancer.”

Doctors and researchers categorize cancer into groups according to genetic information, per the Mayo Clinic. Luminal B breast cancer is estrogen receptor-positive, which means the cancer cells rely on estrogen to grow. So, if estrogen production is stopped with treatment, the cells will ideally stop growing too, according to the National Cancer Institute.

Luminal B is also typically HER2 negative. HER2 is the protein that helps breast cancer cells grow, per the American Cancer Society. When it's negative, that means the cancer isn't likely to respond to drugs that target HER2.

You can also expect luminal B cancer to be progesterone receptor-negative, meaning it won't respond very well to hormone therapy.

"About 15-20% of breast cancers are luminal B tumors," according to Susan G. Komen. "Women with luminal B tumors are often diagnosed at a younger age than those with luminal A tumors."

What is a breast cancer risk assessment?

If it weren’t for her OB-GYN, Dr. Thaïs Aliabadi, Munn said she wouldn’t have been diagnosed for another year. Last year, Aliabadi recommended Munn have her breast cancer risk assessment score calculated. “The fact that she did that saved my life,” wrote Munn.

“A breast cancer risk assessment score is calculated using a mathematical model that incorporates various risk factors that have been shown to be associated with breast cancer,” Dr. Jennifer Plichta, director of the Breast Risk Assessment Clinic at Duke Cancer Institute, previously told TODAY.com.

It can determine your lifetime risk of developing breast cancer and your risk of invasive breast cancer, meaning it spreads outside the milk ducts, of the next five years.

There are at least 24 risk assessment models used to determine someone’s score, according to the Cleveland Clinic. But the most common is the Gail Model which looks at demographic information such as age, race and biopsies, among other considerations. Your doctor can calculate your score for you or you can calculate it using an online tool such as this one from the National Cancer Institute.

“Dr. Aliabadi looked at factors like my age, familial breast cancer history, and the fact that I had my first child after the age of 30,” Munn wrote.

"The way I explained it to my patients (is) if you had a 37.5% chance of boarding a plane that would crash, would you ever board that plane?" said Aliabadi, host of the SheMD podcast, who appeared on TODAY in an exclusive interview. "The answer is almost always no."

Had Munn delayed any longer, Aliabadi said the cancer would have likely grown and "she probably wouldn’t have been early stage."

Munn urged her followers to ask their doctors to assess their likelihood for developing breast cancer. Aliabadi said that if someone's score is higher than 20%, they need annual mammograms starting at 30 years old. Aliabadi also said that she's calculated breast cancer risk for patients as young as 25.

"I want every woman to be their own self advocate at home," Aliabadi said. A mammogram, she added, won't always be enough. "My heart aches when I see these young patients with stage 4 breast cancer," she said, because she believes they could have caught it earlier had they had an assessment.

It's worth noting that the risk assessment tools are population-based and can only determine your average risk among those in your demographic, TODAY.com previously reported. It can’t provide a prediction about whether you'll have breast cancer or not.

What treatment did Olivia Munn have?

As part of her treatment, Munn said she’s had four surgeries in the past 10 months, including a double mastectomy, when both breasts are removed. In that time, she said she’s “learned more about cancer, cancer treatment and hormones,” than she could have imagined. And she thanked family, friends and the breast cancer patients she’s connected with over the past year for their support.

She also wrote about being thankful to partner John Mulaney “for the nights he spent researching what every operation and medication meant and what side effects and recovery I could expect.” And she expressed her gratitude for his being there when she went into and came out of surgery.

Since receiving her diagnosis, Munn has been intentional about maintaining her privacy. “I needed to catch my breath and get through some of the hardest parts before sharing,” she wrote.

Before now, she’d only let people see her when her energy levels were high, she was able to get dressed, leave the house and take her son, Malcolm, to the park, she added. She “tabled” all emotions, noting that she’s only cried twice.

In a video that Munn shared on Instagram, Aliabadi hugged Munn who was in a hospital bed and dressed in a surgical gown and cap, Aliabadi told Munn to do this for her son before Munn said, “I’m ready.”

Munn also included photos of herself receiving a mammogram, getting an exam and the framed photo of Mulaney and their son that she woke to after surgery.

On Instagram, Aliabadi called Munn “brave” and celebrated her for “inspiring countless women. Unfortunately, numerous women are unaware of their elevated lifetime risk and may end up with breast cancer at a more advanced stage. Olivia your courage shines a light on those suffering in silence. I’m so proud of you.”

Despite being diagnosed with cancer so young, Munn said she feels "lucky."

“We caught it with enough time that I had options,” she wrote. “I want the same for any woman who might have to face this one day.”

This article was originally published on TODAY.com