Breast cancer is a disease that gets a fair amount of attention, but not all breast cancers are the same. Triple-negative breast cancer is the rarest and most aggressive form of the disease, affecting only about 15 percent of all breast cancer patients.
“There are many different types of breast cancer, and clinically we group them according to three receptors: the estrogen receptor, the progesterone receptor and the human epidermal growth factor 2/neu (HER2) receptor. Breast cancers that lack these receptors are called triple-negative breast cancers,” medical oncologist and breast cancer specialist Dr. Cesar Santa-Maria, assistant professor of oncology at Johns Hopkins University School of Medicine, said.
Overall, breast cancer affects 1 in 8 women in her lifetime, said Dr. Priyanka Sharma, an oncologist studying triple-negative breast cancer at the University of Kansas Cancer Center.
A person faced with illness often hopes for a definitive test that can reveal the medical issue and lead to treatment and a cure. For people with triple-negative breast cancer, that test doesn’t exist, Sharma said.
“We define triple-negative breast cancer by what it isn’t. When you define something by what it is not, it’s harder to treat,” she said.
What is it?
About 70 percent of breast cancers grow in response to estrogen or progesterone hormones. About 15 percent of breast cancers are HER2-positive. Triple-positive breast cancers occur when cancer cells test positive for estrogen and progesterone receptors as well as HER2 protein. Triple-negative breast cancers test negative for all three.
Dr. Azmina Patel, a physician with Texas Oncology in Sherman, said the other forms of cancer typically feed off of these naturally-occurring hormones, but triple-negative breast cancers do not. This makes it a form of cancer difficult to treat, as there is little targeted treatment available at this time.
Other ways triple-negative breast cancers stand out are that they grow faster, are more likely to return after treatment with a poorer prognosis, and are more likely to affect women before ages 40 or 50.
Patel said triple-negative breast cancer makes up about about 200,000 cases each year, or 20 percent of all cases worldwide. Beyond race and age factors, Patel said other risk factors appear to be genetic in nature. Patel said mutations in the breast cancer genes 1 and 2, also known as BCRA genes, have been tied to the development of triple-negative breast cancer.
“Although triple-negative breast cancer is less curable than other forms of breast cancer, it is still a curable cancer,” Sharma said, explaining with standard treatment of surgery, radiation and chemotherapy about “70 percent of patients with non-metastatic (such as stage I, II or III) triple-negative breast cancers are cured. So you could say the survival rates are 70 percent.”
Targeted drugs like anti-estrogen agents and anti-HER2 drugs that work for the other three types of breast cancer won’t work for triple-negative breast cancer. Treatment requires a more tailored approach, and patients may benefit from participating in a clinical trial, experts agreed.
“I would encourage patients to discuss with their oncologists clinical trial options for those newly diagnosed with triple-negative breast cancer, whether in early or advanced stages. It is through research that we can bring about better treatments, and often clinical trials can provide access to novel agents that are not yet available in clinic,” Santa-Maria said.
To gather more information about the disease and what causes it, Sharma created a triple-negative breast cancer registry in 2011.
“The main goals of the registry are to improve our understanding of clinical and biological aspects of triple-negative breast cancers and genetic cancers. This registry is open at 13 locations in our region and has more than 900 participants,” Sharma said.
Within the umbrella of triple-negative breast cancer, Sharma believes subtypes exist. Once these are better understood, specific treatments can be created based on what is best for each woman, Sharma said.
“We are all very hopeful for the future. There are several new agents/targeted drugs that have shown promise in early studies,” Sharma said. “Since triple-negative breast cancer is a heterogeneous disease we expect that over the course of time several different targeted drugs would need to be employed in clinic to improve outcomes for this sub-type. In other words, there is no single triple-negative breast cancer. There are instead many different diseases in this subtype that may each require different, targeted drugs.”
Numerous treatment strategies are in the works.
“One promising area of research is to use immunotherapy. Immunotherapy can stimulate a patient’s own immune system, allowing the immune system to attack and kill cancer cells,” Santa-Maria said.
Additionally, there is hope for using immunotherapy-based combinations, such as with chemotherapy, he said.