OMG: The Women's Health Brief

After my last post about breast cancer risk factors, a few people asked me how doctors estimate a woman’s individual risk of developing breast cancer.

Two of the most commonly used tools are the Gail Model and the Tyrer–Cuzick Model. I didn’t even know anything about them myself until I listened to a podcast with Olivia Munn on the SHE MD podcast, where Olivia Munn talks about the test that saved her life. She was talking about the Tyrer–Cuzick Model.

These tests are risk assessment tools. They are not diagnostic tests. They don’t tell you whether you will get breast cancer. But they do estimate the probability based on certain known risk factors.

The Gail Model is one of the oldest and most widely used breast cancer risk calculators. It estimates a woman’s five year risk and lifetime risk of developing breast cancer. It looks at factors such as age, age at first period, age at first childbirth, the number of breast biopsies you have had, whether atypical hyperplasia such as ADH or ALH has been found, and whether you have any first degree relatives with breast cancer.

Like many things in medicine, it has limitations. The Gail Model does not take into account breast density, extended family history such as aunts or cousins, paternal family history, or genetic mutations like BRCA1 or BRCA2. Because of this it can sometimes underestimate risk, particularly in women with a stronger family history.

The Tyrer–Cuzick Model, also known as the IBIS model, is more comprehensive and is often used in breast clinics, especially for women considered to be at higher risk. It includes a broader range of factors including detailed family history, breast density, prior biopsies, findings such as ADH, ALH or LCIS, body mass index, hormone replacement therapy use, and the probability of carrying genetic mutations.

One reason the Tyrer–Cuzick model is often used in breast clinics is that it includes breast density as one of the factors when calculating risk. As I mentioned in my previous post, about half of women have dense breasts, and higher breast density can both increase breast cancer risk and make cancers harder to detect on mammograms. Including breast density in risk models is one way doctors try to build a more complete picture of a woman’s individual risk.

These types of findings are often discovered incidentally. In my own case, ALH was found on biopsy, and LCIS was discovered later, which is one of the reasons I have spent so much time trying to better understand breast cancer risk.

The Tyrer–Cuzick model estimates both ten year risk and lifetime risk.

Doctors sometimes use these models to help guide decisions about screening and prevention. Depending on the calculated risk, this might include earlier screening, MRI in addition to mammograms, genetic counselling, preventive medication, or closer monitoring. In many guidelines, a lifetime risk of around twenty percent or higher may qualify someone for additional screening such as annual MRI. In my experience doctors aren’t always keen on MRIs because there can be more false positives that then cause a lot of anxiety.

My risk was around 39%. I knew it would be high but didn’t expect it to be that high. To be honest, it is hard to know the exact answer to every question, especially in the more detailed Tyrer–Cuzick assessment, but I think all women should do it once.

Many breast clinics will calculate your Tyrer–Cuzick score for you, but there are also versions of the assessment available online. One widely used version is the IBIS Breast Cancer Risk Evaluation Tool, which allows women to enter their own information and estimate their risk.

Like most things related to breast cancer, these tools are not perfect. They are based on population data and probabilities rather than certainty. But they can still be useful in helping us and our doctors have more informed conversations about screening and prevention.

Understanding your personal risk is important. It helps us make informed decisions. I am always surprised that it isn’t more widely known and that more women aren’t encouraged to calculate their risk. Knowledge really does give us the power to make better choices about our health.

Reference

SHE MD Podcast – Episode: “Olivia Munn’s Breast Cancer and the Test That Saved Her Life.”
Guest: Olivia Munn
Hosts: Dr. Thaïs Aliabadi and Mary Alice Haney
Released: June 4, 2024.