What Is Triple-Negative Breast Cancer?

A USC Norris Comprehensive Cancer Center expert explains the diagnosis and latest treatment for triple-negative breast cancer.

Triple-negative breast cancer is one of the least common types of breast cancer, only accounting for about 15% to 20% of all breast cancer diagnoses. It is one of the most aggressive subtypes of cancer that carries a high risk of metastasis. But a new treatment has come available recently that is making a difference for patients who receive this diagnosis.

What does triple-negative breast cancer mean?

Triple-negative breast cancer is named for what it is not. When diagnosing breast cancer, tumors are tested for the presence of estrogen or progesterone receptors or high levels of human epidermal growth factor receptor 2, or HER2, because these are what fuel the growth of most breast cancers. When none of these exist, the disease is classified as triple-negative breast cancer.

How is it typically found?

It is most often found through routine breast cancer screening, though some people also notice a change in the shape of their breast or the way it feels. As with other breast cancers, regular routine screening helps because triple-negative breast cancer is most treatable when it is found in its earliest stages.

What is the treatment for triple-negative breast cancer?

Treatments that target estrogen and progesterone receptors or HER2 are ineffective against triple-negative breast cancer. But chemotherapy, immunotherapy and surgery — or some combination of the three — are typically used to combat triple-negative breast cancer. The exact treatment for triple-negative breast cancer depends on the size of the tumor and the stage of the cancer.
 
“We tailor the approach to the needs of the individual and their cancer,” says Daphne Stewart, MD, an oncologist specializing in treating breast cancer with the USC Breast Center and the USC Norris Comprehensive Cancer Center, part of Keck Medicine of USC.

How has the treatment for triple-negative breast cancer changed in recent years?

There has been some good news for treating triple-negative breast cancer recently. A type of immunotherapy called pembrolizumab, as this drug is known, was approved for use against triple-negative breast cancer in 2021. It is typically used in conjunction with chemotherapy and has been shown in clinical trial to reduce the risk of progression, recurrence and death from breast cancer.
 
“It is such a breakthrough and is truly saving lives,” says Dr. Stewart. “We are inspired by the results and are so happy to have this now for our patients.”
 
Because triple-negative breast cancer is aggressive, time is of the essence. At the USC Breast Center, new patients meet a team of specialists on their first visit. That visit typically includes medical oncologists, radiation oncologists, surgeons, plastic surgeons and genetic counselors.
 
“It is important with triple-negative breast cancer that patients have a team they trust and that is working together to save that patient,” says Dr. Stewart, adding that not all providers have teams of doctors like this. “This does require aggressive therapy and a team approach.”
 
Dr. Stewart adds that breast cancer patients at the USC Breast Center also have access to a breast cancer survivorship clinic in addition to their standard follow-up visits. This clinic helps patients manage any side effects they may develop because of their prior treatments. They receive counseling from their team about optimizing their long-term health following treatment. The clinic helps patients stay on top of their cancer screenings and makes sure family members are appropriately screened if there is a higher genetic risk factor.
 
“Our goal with the survivorship clinic is to keep our patients as healthy as possible for the rest of their lives,” says Dr. Stewart.

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