Olivia Munn shared a gallery of photos and video on social media recently, revealing she was diagnosed with breast cancer. The actress thanked her family and friends for their support, while providing a detailed explanation of how she became diagnosed.

“I tested negative for all, including BRCA (the most well-known breast cancer gene). My sister Sara had just tested negative as well,” Munn wrote. “We called each other and high-fived over the phone. That same winter I also had a normal mammogram. Two months later I was diagnosed with breast cancer.”

Munn said she suffers from an aggressive, fast moving form of breast cancer known as luminal B. According to the Mayo Clinic, doctors are increasingly using genetic information about breast cancer cells to categorize different kinds of the disease. Knowing which type a patient has can help inform a doctor’s plan for effective treatments.

Luminal B breast cancer patients are likely to benefit from chemotherapy and possibly hormone therapy. Luminal B is an HER2-positive cancer, which according to the Mayo Clinic, means it “tests positive for a protein called human epidermal growth factor receptor 2 (HER2). This protein promotes the growth of cancer cells.HER2-positive cancers are usually more aggressive than other types.

Munn explained her doctor assessed her breast cancer risk assessment score before determining her diagnosis. According to the Susan G. Komen breast cancer foundation seven risk factors are assessed to calculate the score: age, age at first period, age at birth of a first child, family history of breast cancer, race/ethnicity and number of breast biopsies showing atypical hyperplasia.

“Because of that score I went to get an MRI, which led to an ultrasound, which then led to a biopsy,” Munn wrote. “The biopsy showed I had Luminal B cancer in both breasts.”

Munn said she considers herself “lucky” for catching the cancer early enough to have treatment options.

“I want the same for any woman who might have to face this one day,” she wrote. “Ask your doctor to calculate your Breast Cancer Risk Assessment Score.”