The Your Friends and Neighbors star, 45, took to Instagram on Wednesday and revealed that her mom was diagnosed with Stage 1 HER2 breast cancer after Munn's own breast cancer diagnosis in 2023.
According to the Susan G. Komen foundation, the test is a tool "often used by health care providers to estimate breast cancer risk."
Dr. Jennifer Ashton, former ABC News chief medical correspondent and a board-certified OB-GYN, said in a 2024 interview that the test "helps to provide an actual numerical risk for lifetime risk of breast cancer and breast cancer diagnosis in the next five years."
According to the American College of Radiology, people with 20% or greater lifetime risk of breast cancer are considered high risk.
The American Cancer Society describes HER2 as a "protein that helps breast cancer cells grow quickly."
"Breast cancer cells with higher than normal levels of HER2 are called HER2-positive," the ACS states. "These cancers tend to grow and spread faster than breast cancers that are HER2-negative, but are much more likely to respond to treatment with drugs that target the HER2 protein."
The Tyrer-Cuzick model, or IBIS, is a type of breast cancer risk calculator. According to the American College of Obstetricians and Gynecologists, this calculator is one of a few options that physicians can use to calculate lifetime risk of breast cancer.