A Wake-Up Call for Women

Her doctor did an individual risk assessment, finding Munn’s lifetime risk was 37%, considered very high, and referred her to more extensive testing, which detected cancer in both breasts.

Munn said in a series of Instagram posts that she initially kept her diagnosis private, explaining, “I needed to catch my breath and get through some of the hardest parts before sharing.” She lauds her OB/GYN, Thais Aliabadi, MD, who decided to calculate the risk score. “The fact that she did saved my life,” Munn wrote. 

Munn’s fighting spirit and positive attitude are apparent. “I’m lucky,” she posted. “We caught it with enough time that I had options.” She praised the efforts of John Mulaney, her partner with whom she shares a 2-year-old son. He researched treatments and medication and posted pictures bedside of their son.

A spokeswoman for Munn said the actress is not doing interviews at this time. Spokespersons at Cedars-Sinai declined to comment on Munn’s case.

Genetics and Breast Cancer 

“Most people who get breast cancer don’t have an inherited genetic mutation,” said Nathalie Johnson, MD, medical director of the Legacy Health Systems Cancer Institute and the Legacy Breast Health Centers in Portland, OR, who was not involved in Munn’s treatment. 

“Only 5 to 10% of people who get breast cancer have a gene that tests positive,” agreed Joanne Mortimer, MD, director of Women’s Cancers Program and a medical oncologist at City of Hope in Duarte, CA. Mortimer was also not involved in Munn’s care and spoke generally about breast cancer treatment in cases similar to Munn’s.

Cancer Subtypes

Luminal breast cancers are those originating inthe luminal or inner lining of the mammary ducts. Both luminal A and luminal B need estrogen to grow, Johnson said. Luminal A has a better prognosis and is easier to treat. Luminal B has a worse prognosis, she said, and it’s sometimes dubbed B for “bad.” 

Luminal B “requires chemotherapy and if it recurs; it’s just harder. It stops responding to endocrine therapy or estrogen-blocking drugs and so we have to use other therapies.” 

Genomic testing helps doctors decide if the luminal tumors are A or B forms, she said. The prognosis for luminal B cancers can still be good, Johnson said.

Beyond Mammograms

“Mammograms aren’t perfect,” Johnson said. The screening can especially miss cancers in breasts with dense tissue because the cancers don’t show up as well on the imaging. 

Density refers to the amount of fibrous and glandular tissues in the breast compared to fatty tissue. About half of women age 40 and above have dense breasts, according to the CDC. The mammogram report may include information about whether breast density is high or low. 

Even if mammogram results show no evidence of cancer, if a woman feels something unusual in her breasts, it’s time to return to the doctor and ask about further testing, Johnson said.

An MRI is often done in women as young as Munn, Mortimer said, if they are known to have dense breasts or a family history, both known to raise breast cancer risk. “In someone with a family history, we alternate MRIs with mammograms to increase the chances of detection,” she said.

Individual Assessments

In her Instagram posts, Munn praises her OB/GYN for suggesting an individual risk assessment. “Dr. [Thais] 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 on Instagram. “She discovered my lifetime risk was at 37%.” 

That score prompted the doctor to refer Munn for an MRI and then an ultrasound and biopsy. “The biopsy showed I had Luminal B cancer in both breasts,” Munn wrote. “Luminal B is an aggressive, fast-moving cancer.” Thirty days later, Munn had a double mastectomy.

One such risk assessment is on the National Cancer Institute site. It takes into account a history of breast cancer, previous radiation to the chest, genetic mutations, age, race, ethnicity, history of a breast biopsy with a benign diagnosis, age at first menstrual period, age when first child was born (over 30 raises risk), and first-degree relatives (your parents, sibling, or child) with breast cancer.

From that, it predicts a 5-year risk and a lifetime risk of developing breast cancer, comparing the patient’s risk with the average risk of the population.

For instance, a 43-year-old White woman with no history of breast cancer or previous radiation, no genetic mutations, no previous breast biopsies, first period at age 12, 30 or older at first childbirth, and no first-degree relatives with breast cancer has a 13.2% lifetime risk of breast cancer, slightly above the average risk of 12.1%.