Let's Talk About the Causes of Breast Cancer

We’ve all heard the statistic: One in eight women will get breast cancer at some point during her life. What we really want to know is whether there’s any way to predict if that one in eight will be... us.

by Sunny Sea Gold Health Writer

Among the many challenges of breast cancer is the fact that it’s hard to know who will get it. Sure, scientists can now test people for breast cancer genes, but most women who develop the disease don’t have a family history. That said, there are several well-known risk factors—and understanding what they are can help you get the screening you need and take action to reduce your chances of developing breast cancer.

Breast Cancer Causes

Our Pro Panel

We went to some of the nation’s top experts in breast cancer to bring you the most up-to-date information possible.

P. Hank Schmidt, M.D.

P. Hank Schmidt, M.D.

Breast Surgical Oncologist

Mount Sinai

New York, NY

Jonathan Stegall, M.D.

Jonathan Stegall, M.D.

Medical Director

The Center for Advanced Medicine

Alpharetta, GA

Zahi Mitri, M.D.

Zahi Mitri, M.D.

Breast Cancer Oncologist

The OHSU Knight Cancer Institute

Portland, OR

Breast Cancer Causes
Frequently Asked Questions
What are the risk factors for breast cancer?

The two biggest risk factors for breast cancer are also things you can’t do anything about: Being a woman and getting older. In addition, having a BRCA 1 or 2 gene mutation greatly increases your risk, as well as a strong family history, going through puberty early, hitting menopause later, and using hormone replacement therapy.

What are my chances of getting breast cancer?

Every person's risk is different and depends on factors such as genetics, family history, lifestyle, and other issues. The average woman has a 12% chance of developing breast cancer at some point in her life. The median age of diagnosis is 62; only about 5% of women with breast cancer are diagnosed under age 40.

What are the best ways to detect breast cancer?

Get to know your breasts—how they feel and look, and how they change during your menstrual cycle. Symptoms include lumps, dimpled skin, and pain or swelling in one breast that doesn't come and go with menstrual cycles. Many breast cancers cause no obvious symptoms, however, which is why regular mammogram screenings are incredibly important.

Can deodorant cause breast cancer?

No, this is a myth. Many years ago, some scientists noted that deodorants are applied very close to the breast, often on freshly shaved skin, and wondered whether aluminum and other common ingredients could contribute to breast cancer. A few studies were done and no link was found, according to the National Institutes of Health.

What Is Breast Cancer Again?

Breast cancer is the most common type of cancer in women—about 270,000 women are diagnosed each year, accounting for approximately 30% of all cancer cases, according to the American Cancer Society. Although it happens much less often, men can develop breast cancer, too.

In each of these people, breast cancer began the same way: A rogue cell began to multiply in ways it’s not supposed to, usually in the milk glands (called lobules) or the ducts that carry milk, eventually forming a tumor.

How each person's breast cancer develops from there depends on lots of variables. But importantly, most breast cancers are highly treatable. On average, the five-year survival rate (meaning: the percentage of people who are still living five years after diagnosis) for breast cancer that has not spread to other parts of the body is 90%.

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So What Causes Breast Cancer?

Exactly what triggers breast cells to go rogue and grow out of control still isn’t well understood, but we do know that certain factors and habits can interfere with a cell’s instruction manual, a.k.a., its genes.

Without this instruction manual telling cells when to stop dividing or how to repair DNA damage, abnormal cells will just keep on going until a tumor forms.

Let’s take a look at some of the factors that influence your risk for developing breast cancer, including genetics, family history, lifestyle, and other issues.

Is Breast Cancer Genetic?

It can be. Mutations in two particular genes can greatly increase your risk of getting breast cancer.

These genes, known as BRCA1 and BRCA2, make proteins that help patch up broken DNA and keep cells stable.

But when they mutate, the proteins no longer work correctly and cells may start acting in ways they shouldn’t—including turning cancerous. Mutations in BRCA genes also boost women’s risk of ovarian cancer.

The average woman has a 12% risk of developing breast cancer at some time in her life. But women with a BRCA1 or 2 mutation have a 50% to 85% risk of getting it. One large study recently found that 72% of women with the BRCA 1 mutation eventually got breast cancer by age 80, and 69% with a BRCA 2 mutation did.

The other thing that BRCA mutations do is bump up the risk of developing cancer in both breasts. Research shows that women with a BRCA mutation who develop cancer in one breast have a 26% to 40% chance of getting a tumor in the other.

Men with these mutations also have an increased risk of developing breast and other cancers.

Does Family History Play a Role?

Even if BRCA gene mutations don’t run in your family, having close relatives with breast cancer still makes it more likely that you will get it, too. Any of the following family connections increases your chances of developing breast cancer:

  • Having a mother, sister, or daughter who got breast cancer before age 40; or having two of these relatives diagnosed before age 50

  • Having a father, son, grandfather, grandson, or uncle diagnosed with breast cancer at any age

  • Having two or more close relatives (parents, grandparents, children, siblings, aunts, and uncles) with breast cancer

  • Having one close relative with breast cancer and one with ovarian cancer

  • Having one close relative with cancer in both breasts

If any of these combos rings true to your own life, it’s time to talk with your doctor about more advanced screening for breast cancer.

Is Age a Breast Cancer Risk Factor?

Yes, age is a major risk factor. The vast majority of cases happen in people 50 years or older.

A possible reason: Sometimes it takes decades of little gene mutations to accumulate before finally tipping the balance and triggering a tumor.

At age 30, a woman’s risk of being diagnosed with breast cancer in the next 10 years is less than 0.5%. By age 50 it’s a little over 2%, and at 70 it’s 4%.

Does Hormone Replacement Therapy Cause Breast Cancer?

Some breast cancers are fueled by estrogen and progesterone, and the longer a woman is exposed to these reproductive hormones, the higher her risk of breast cancer.

So yes, taking combined estrogen and progesterone hormone therapy for menopause symptoms does increase breast cancer risk—although the benefits of those therapies may outweigh the drawbacks for some women.

Exactly how much they increase your risk depends on how old you are and how long you take the medications. A history of using certain oral contraceptives for birth control is also linked to a very small (7%) increase in risk.

Women who start their periods early, or hit menopause late, also have a 20% to 30% higher risk, possibly because of longer exposure to these hormones.

Does Smoking Cause Breast Cancer?

Studies have found a link between smoking and breast cancer, but more research is being done to confirm the link and figure out why.

One well-regarded study found a 9% increase in risk for former smokers, and a 16% increase for current smokers. Other studies have suggested that the more cigarettes you smoke per day, the higher the risk.

What About Drinking and Breast Cancer?

Whether or not you consume alcohol is a personal choice you’ll make, but it is worth saying that even moderate drinking (one to two drinks a day) may increase the risk of breast cancer by 30% to 50%, according to a study in Current Breast Cancer Reports.

Can Excess Body Fat Raise Your Risk?

Body fat produces estrogen, so the more you have, the higher your hormone levels tend to be. A study in JAMA Oncology found that in post-menopausal women, the risk of an estrogen-sensitive tumor was nearly double in those with the highest percentage of body fat compared to the lowest. This was true even for women who had a “healthy” body-mass index.

Does Having Kids Make a Difference?

Whether you have kids or not, and at what age, can affect your breast cancer risk by changing your exposure to pregnancy-related hormones.

Some research suggests that women who never have children are up to 30% more likely to develop the disease than moms. How old you are when you become pregnant may count, too. Some studies have found that women who have their first baby after age 35 are 40% more likely to get breast cancer than those who had a kid before age 20.

Obviously, no one is suggesting that you decide whether or not to have kids based on a cancer risk. After all, two of the biggest risk factors—being female and getting older—are things you can't do anything about. But since treatment success increases the earlier breast cancer is caught, it's helpful to know which variables make you more susceptible, so you can stay one step ahead of the disease.

Sunny Sea Gold
Meet Our Writer
Sunny Sea Gold

Sunny is a health journalist with deep expertise in women's and children’s health who has written for some of the largest and most well-known print and digital publications in the United States. She’s also the author of the book Food: The Good Girl’s Drug, and writes essays and reported pieces on body image, eating disorders, parenthood, and mental health. She lives in Portland, OR, with her husband and two daughters.