Understanding Breast Cancer: Risk Factors, Prevention & Early Detection

Self-advocacy starts with knowledge 💪

Oct 22, 2024

ICYMI 👉

I regularly field questions from patients about breast cancer: Do I need a breast MRI? Or does a regular mammogram suffice? Should I have genetic testing if my grandmother had breast cancer? What can I do to reduce my risk?

So, in honor of Breast Cancer Awareness Month, today I‘ll take a deeper dive into breast cancer—what we know about it, how to assess your own risk, and what proactive steps you can take to lower that risk.

slice grapefruit — Photo by charlesdeluvio on Unsplash

Breast Cancer in Numbers

It might seem like everywhere you turn, someone you know has breast cancer. That’s probably because it is the most common cancer diagnosed in women worldwide. In the U.S., an estimated 1 in 8 women (about 13%) will develop invasive breast cancer at some point during their lifetime. This year alone, more than 280,000 new cases of invasive breast cancer will be diagnosed in American women, 16% which will occur in women under the age of 50. In addition, approximately 51,000 cases of ductal carcinoma in situ (DCIS), a non-invasive form of breast cancer, will be diagnosed this year. While these numbers may feel daunting, the good news is that with advances in early detection and treatment, survival rates continue to improve. In fact, for women with localized breast cancer, the 5-year survival rate is 99%.

Men can develop breast cancer, too! While less than 1% of all breast cancers occur in men, it’s important for men to understand the risk factors.

Risk Factors, Fixed versus Dynamic

The risk factors for breast cancer fall into two buckets—those we can control and those we can’t. The key is understanding the difference.

Let’s start with risk factors beyond our control. First is age, an undeniably unchangeable factor. The risk of developing breast cancer increases as we age, with the majority of cases occurring in women over the age of 50. This makes sense intuitively if you remember that cancer occurs as a result of accumulated mutations in cells that happen over time. In short, the more time you spend on the planet, the more opportunities your cells have to mutate.

Genetics also play a significant role in breast cancer risk. About 5-10% of breast cancers are linked to inherited gene mutations, such as those in the BRCA1 and BRCA2 genes. Women with a BRCA1 mutation, for example, have a 55-72% lifetime risk of developing breast cancer, while those with a BRCA2 mutation have a 45-69% risk. Other gene mutations, like PALB2, TP53, and CHEK2, also increase risk but are less common.

Family history is another factor. Having a first-degree relative (e.g., a mother, sister, or daughter) with breast cancer nearly doubles your risk, especially if the cancer occurred at a younger age.

A few words about genetics and family history: it’s important to know that the vast majority of breast cancers are not caused by inherited mutations. In fact, about 85% of breast cancers occur in women with no family history. I want to say that again in order to dispel the myths that 1) if you don’t have breast cancer in your family, you are in the clear, and 2) if you do have breast cancer in your family, you are destined to get it. These are indeed myths! If you are wondering about the relevance of your family history and genetics to your cancer risk, consider consulting a genetic counselor. Your insurance is more likely to pay for genetic testing if you have a strong family history (first degree relative with breast cancer) and a family history of early breast cancer (premenopausal), because these are the factors that can suggest an inherited mutation/predisposition for breast cancer.

Breast density is another risk factor that often goes unmentioned but plays a significant role. Women with dense breasts (which means that the breast tissue is more fibrous and glandular tissue than fatty tissue) have a higher risk of breast cancer—not because dense breast tissue is inherently more risky but because dense tissue tends to make mammograms more difficult to interpret. So, if you have dense breasts, talk with your doctor about getting additional imaging, like MRI or ultrasound (see below).

Next, let’s talk about the modifiable risk factors—the things you can influence. Lifestyle choices and underlying health conditions play a significant role in breast cancer risk. Here’s what we know:

Weight: Postmenopausal women who are overweight or obese have a higher risk of breast cancer. Excess adipose (fat) tissue increases estrogen levels, which can stimulate certain types of breast cancer. Focusing on a balanced diet with plenty of vegetables, fruits, lean proteins, and whole grains can make a big difference.
Physical activity: Regular exercise has been shown to lower breast cancer risk by keeping body weight in check and reducing inflammation. The American Cancer Society recommends at least 150-300 minutes of moderate exercise each week to help reduce the risk of certain cancers.
Alcohol consumption: Even moderate drinking can increase your breast cancer risk. Women who have 1 alcoholic drink per day have a 7-10% increased risk, and the risk increases with each additional drink. The American Cancer Society recommends limiting alcohol to no more than one drink per day, however the less alcohol you consume the better.
Regular screenings and vigilance. You also have control over your screenings. Women at average risk should start annual mammograms at age 40, while women at high risk (with a strong family history or genetic predisposition) may need to start earlier and incorporate additional screening methods like MRI. (See below.)
Breastfeeding. We know that women who breastfeed have a lower risk of breast cancer. So breastfeed your babies if you are able!

What about the rumors that dietary sugar, aluminum-containing underarm deodorants, carrying your cell phone in your bra, or simply wearing a bra cause breast cancer? There is no current evidence to support any of these.

What about Hormone replacement therapy (HRT) and breast cancer? It is absolutely true that a hormone-sensitive breast cancer (one that already was going to occur, with or without HRT) can be stimulated by estrogen and/or progesterone, regardless of whether the hormones are produced by a woman’s ovaries or taken in the form of HRT. However HRT does not cause breast cancer. Is HRT risk-free? Not at all. Do we recommend discontinuing HRT in patients who develop a hormone-sensitive tumor? Absolutely. But when we’re talking about HRT and breast cancer, it’s important to distinguish between causation and correlation because far too many women have been deprived of HRT, being told that “HRT causes cancer.”

Early Detection is Key

The key to surviving breast cancer is early detection. Mammograms remain the gold standard for catching breast cancer early, often before any symptoms (e.g., palpable masses) appear. For women with dense breasts or high risk, adding breast MRI or ultrasound can help spot cancers that a mammogram might miss.

That said, there is a lot of conflicting advice out there on mammograms—how often to get them, at what age women should be screened and at what age to stop. In the U.S., there are seven different screening guidelines from various expert groups. Which one to follow?

One useful tool in the conversation about risk is the Tyrer-Cuzick model, which helps assess a woman’s lifetime risk of developing breast cancer by factoring in a range of variables, including age, height, weight, family history of breast or ovarian cancer, and personal screening history. This tool is an incredibly valuable resource for identifying women who may benefit from more personalized screening or even a genetics consultation.

I suggest trying the calculator yourself here.

Let me give you an example from my own experience. After entering my own details into the model, I received this estimate: Based on the information provided, my lifetime risk of developing invasive breast cancer is 9.6%. For comparison, the average lifetime risk for U.S. women of my age is 9%. While my result doesn’t place me at high risk, it’s empowering to know where I stand and what steps I can take to stay proactive.

Now, here’s where it gets really important—if your lifetime risk is 20% or greater, you fall into the high-risk category for developing breast cancer. In this case, yearly screening with breast MRI is recommended, in addition to mammograms. If an MRI isn’t feasible, other options like contrast-enhanced mammograms (CEM) or molecular breast imaging (MBI) are alternatives. If those are not available, ultrasound can be considered.

If you have less than a 20% lifetime risk but who have dense breasts, it’s still worth considering yearly MRI in addition to mammograms. Again, CEM or MBI are solid alternatives, and if those aren’t accessible, ultrasound is a useful fallback option.

And finally, if your risk is below 20% and you don’t have dense breasts, the recommendation is to follow standard screening guidelines for women at average risk. That means yearly mammograms beginning at age 40.

As a brief aside, here are two common questions I get about mammography:

First, from patients who have been told to get a supplemental breast MRI or breast sonogram/ultrasound: Why bother with the mammogram if I’m getting an MRI or sonogram? The answer is that mammograms, sonograms, and MRIs look at breast tissue in distinct and important ways. Some types of breast cancer that are seen on a mammogram are missed on MRI, and vice versa.
Second, from patients in general: Can mammograms do more harm than good? The answer is it depends on the person’s unique risk factors. Indeed there is data to suggest that mammograms can lead to overdiagnosis and overtreatment of breast cancer, especially for women under age 40.

Upshot #1: I suggest bringing the Tyrer-Cuzick score to your next doctor’s appointment. It can help direct decision-making on the best breast cancer screening plan for YOU.

Upshot #2: In order to save lives and to reduce unnecessary testing, more work needs to be done to tailor breast cancer screenings to the individual. If you’re interested in being part of the solution, consider enrolling in a large scale clinical trial comparing usual screenings with more personalized screenings for breast cancer. The WISDOM trial was started by UCSF breast cancer expert Dr. Laura Esserman. To enroll, you have to be between ages 30 and 74, live in the U.S., and have no personal history of breast cancer or DCIS. To learn more or sign up, click here. (Note that I do not benefit in any way from this; I just think it’s cool. This is how we advance science!)

Treatment: We’ve Come a Long Way, Baby

Thanks to advances in research and technology, breast cancer treatment is becoming more personalized and effective. Of course treatment options depend on the type of breast cancer and its stage but generally include surgery, radiation therapy, chemotherapy, hormone therapy, and targeted therapies that focus on specific cancer cells.

For early-stage breast cancer, surgery (lumpectomy or mastectomy) is often combined with radiation to minimize recurrence. For more advanced cancers, chemotherapy may be necessary. Hormone therapies like tamoxifen and aromatase inhibitors are used to treat hormone-receptor-positive cancers by blocking estrogen's effects on breast tissue.

The development of targeted therapies like HER2 inhibitors and CDK4/6 inhibitors has also opened up new avenues for treatment, improving outcomes and minimizing side effects.

The Upshot: Knowledge is Power

When it comes to breast cancer, knowledge is your best (breast? 🥴) friend. Whether it’s through lifestyle changes, regular screenings, or engaging in conversations with your doctor about your risk, there are concrete steps to put yourself in the driver’s seat of your health.

What questions do you have? I’m all ears!