There’s currently no clear answer to what causes triple-negative breast cancer, but it’s strongly associated with a family history of breast cancer and certain gene mutations, particularly BRCA1.

When you’re diagnosed with triple-negative breast cancer (TNBC), many questions likely come to mind. TNBC represents only about 15% to 20% of all breast cancers, so you might want to know why you have this particular type.

Researchers haven’t been able to determine exactly what causes a person to develop TNBC. But there are some risk factors, such as certain inherited gene mutations, associated with TNBC.

This article discusses potential causes and risk factors, recommendations for screening and prevention, plus a few frequently asked questions about TNBC.

Language matters

In this article, we talk about the causes of triple-negative breast cancer in people assigned female at birth.

It’s important to note that not everyone assigned female at birth identifies with the label “female.” However, at times we use “women” or “female” to reflect the language in a study or statistic or to make sure people can find this article with the terms they search.

When possible, we aim to be inclusive and create content that reflects the diversity of our readers.

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There’s no clear answer to what causes TNBC.

It does have a strong association with certain mutations in the BRCA1 gene. BRCA1 is a tumor-suppressing gene because it helps prevent cells from growing out of control. Inheriting these mutations increases the risk of breast, ovarian, prostate, and other types of cancer.

Among women with an inherited BRCA1 mutation, 70% who develop breast cancer have the TNBC subtype. Of course, not everyone who carries this gene develops cancer. And people who don’t carry these mutations also get TNBC, so there are still many unknowns.

Research into the potential causes of TNBC is ongoing.

People of any age and gender can develop TNBC. But it’s mostly diagnosed in females under age 40.

In addition to the BRCA1 mutation, other gene mutations may be associated with TNBC. They include BRCA2, TP53, CDH1, PTEN, and STK11.

African American and Hispanic women have a higher rate of TNBC than White women. About 20% to 40% of breast cancers in African American women are triple negative.

Risk factors for all types of breast cancer include:

  • not being physically active
  • overweight or obesity, especially after menopause
  • certain hormonal contraceptives or long-term hormone replacement therapy (HRT) after menopause
  • alcohol consumption
  • family or personal history of breast cancer

There’s no way to completely prevent any kind of breast cancer. You can’t do anything about certain risk factors, such as being born female, age, and genetics. However, you may be able to lower the risk of developing breast cancer by:

  • being physically active
  • maintaining a healthy weight
  • avoiding or limiting alcohol consumption

Screening recommendations

For women at average risk for breast cancer, the U.S. Preventive Services Task Force (USPSTF) recommends mammography screening every 2 years starting at age 50 and continuing through age 74. The decision to start screening between ages 40 and 49 is left to individuals to decide.

At any age, it’s worth discussing screening options with your doctor. This is especially important if you’re at a higher-than-average risk of developing breast cancer.

Genetic testing

You might want to consider genetic testing and genetic counseling if you have:

Preventive measures

If you’re at a very high risk of breast cancer, it’s a good idea to discuss preventive measures with your doctor. Depending on your risk profile, these may include:

Can stress cause triple-negative breast cancer?

We know that stress affects the body in many ways. But there’s no evidence of a direct cause-and-effect link between stress and TNBC.

Studies on the links between stress and cancer have produced mixed results. One reason is that researchers may have different definitions for stress. It’s also hard to account for the ways individuals cope with stress or how much support they receive.

Another factor to consider is that when you’re under stress, you may develop unhealthy behaviors, such as overeating, becoming sedentary, or drinking alcohol. These are all risk factors for breast cancer.

Some lab and animal model studies suggest that chronic stress may help cancer spread or shorten survival time. But according to the National Cancer Institute, evidence that stress directly affects survival is weak.

Is triple-negative breast cancer the hardest to treat?

TNBC lacks estrogen receptors (ER), progesterone receptors (PR), and HER2. That means this cancer does not respond to hormone therapies such as tamoxifen or targeted therapies such as Herceptin.

Despite fewer options, it is treatable. Treatment for TNBC typically includes:

Chemotherapy can be used to shrink the tumor before surgery (neoadjuvant chemotherapy). It can also be used to target any cells that remain after surgery or cancer cells that may have spread elsewhere (adjuvant chemotherapy).

In addition, immunotherapies like Keytruda are now available to treat TNBC.

Can you survive triple-negative breast cancer?

Yes, triple-negative breast cancer is survivable.

TNBC is more aggressive than most other types of breast cancer. There’s a higher risk of recurrence in the first 2 to 3 years after diagnosis. Among people with stage 1, 2, or 3 TNBC, about 40% have a recurrence after standard treatment. And 60% experience long-term disease-free survival.

The 5-year relative survival rates for TNBC are:

Stage of cancer5-year relative survival rate
Localized: hasn’t spread beyond the breast91%
Regional: spread to nearby tissue or lymph nodes65%
Distant: spread to distant sites such as lungs, brain, or bones12%
All stages combined77%

These are general statistics based on people who were diagnosed between 2011 and 2017. Many factors can affect your outlook, such as age, general health, and choice of treatments. Your doctor can help you understand more about your personal prognosis.

Even with metastatic TNBC, some people have longer-than-average survival.

A case report published in 2019 describes a woman with recurrent TNBC that had spread to her lungs, liver, and ribs. She had intensive chemotherapy and immunotherapy. And 15 years later, she was still alive and there was no evidence of persistent or recurrent metastatic disease.

How important is genetic testing?

Genetic testing can determine if you carry any of the gene mutations associated with TNBC. This can help assess your risk of recurrence. It can also help guide treatment decisions for advanced TNBC.

You can share this information with relatives who may be at increased risk. That gives them the opportunity to consider enhanced screening and cancer prevention strategies.

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TNBC is strongly associated with a family history of breast cancer and certain gene mutations, particularly BRCA1.

Sometimes, carriers of these genes develop other types of breast cancer. Some people with these genes never develop cancer. And people without these gene mutations also develop TNBC.

Exactly why an individual develops TNBC is not clear. Though anyone can get it, it tends to be diagnosed in women under age 40.

While TNBC is more aggressive than most breast cancers, it is treatable.