Although breast cancer is often referred to as one disease, there are actually many different types of breast cancer. The differences can help guide treatment and provide information on prognosis. Certain characteristics make some breast cancers more aggressive than others, leading to a poorer prognosis. One such breast cancer is triple negative breast cancer. Although we understand some aspects of these breast cancers, we still have much to learn.
All breast cancers are tested for hormone (estrogen and progesterone) receptors and HER2/neu receptors. If the test is “positive”, the cancer cells have many receptors. If the test is “negative”, the cancer cells have few or no receptors. The status of these receptors helps guide treatment. Triple negative breast cancers are:
About 14 to 20 percent of all breast cancers are triple negative.1-7
Triple negative breast cancers tend to occur more often in:1,4-6,8-11
Triple negative breast cancers appear to be more common among African American women (especially those who are premenopausal) compared to white women.1,5,10,12-16 Although the reasons for this are not clear, some studies suggest lifestyle factors might play a role. Some findings show African American women tend to have lower rates of breastfeeding, to give birth to more children and to carry excess weight in the abdomen area compared to other women, all of which may increase the chances of having triple negative breast cancer.7,17-20
Inherited mutations in the BRCA1 and BRCA2 genes (BReast CAncer genes 1 and 2) are linked to breast cancer risk. People who carry these mutations have an increased risk of breast cancer (learn more).21
Most BRCA1-related breast cancers and some BRCA2-related breast cancers are triple negative.8-9 The relationship between triple negative cancers and BRCA1 and BRCA2 genetic mutations is under study and may help identify new treatments.
Most risk factors affect the risk of triple negative breast cancer in the same way they affect the risk of other breast cancers. For example, breastfeeding lowers the risk of breast cancer, including the risk of triple negative breast cancer.16,22-23
Some factors, however, appear to impact the risk of triple negative breast cancers differently than they impact the risk of other breast cancers.
In general, women who have given birth to more than one child have a lower risk of breast cancer than women who have never given birth. However, women may not get this protective benefit of childbearing for triple negative breast cancers.7,16,19 On the other hand, although having a child a later age tends to increase the risk of breast cancer, it does not appear to increase the risk of triple negative cancers.7 These topics are under active study.
Being overweight tends to lower the risk of breast cancer before menopause and increase the risk of breast cancer after menopause.24-26 However, being overweight may increase the risk of both premenopausal and postmenopausal triple negative breast cancer.7
Triple negative breast cancers are treated with a combination of surgery, radiation therapy and chemotherapy. Because triple negative breast cancers are ER-, PR- and HER2-, they cannot be treated with hormone therapy (only used to treat estrogen receptor-positive and progesterone receptor-positive cancers) or trastuzumab (Herceptin) (only used to treat HER2/neu-positive cancers). Fortunately, chemotherapy can be effective in treating these breast cancers.
Sometimes chemotherapy is given before surgery (called neoadjuvant chemotherapy), rather than after surgery. Neoadjuvant chemotherapy can increase a woman’s breast surgery options. It can shrink a tumor enough that a lumpectomy becomes an option to a mastectomy. The response to neoadjuvant chemotherapy may also give information on prognosis. If a triple negative tumor responds well to neoadjuvant chemotherapy, the chances of survival are higher than when there is a poor response to this early treatment.27-28
Triple negative breast cancers appear more likely to recur than other breast cancers.29 Recurrence for these cancers often involves metastasis (when cancer spreads to other organs), especially to the brain or lungs. Triple negative breast cancers tend to recur within a few years and when they recur, prognosis is usually poor.29-30
However, because triple negative breast cancers tend to recur early, if a woman survives five years without a recurrence, her chances of survival are high.29 This is good news for five-year survivors and makes this milestone especially important for women diagnosed with triple negative breast cancer.
Although many triple negative breast cancers can be successfully treated, overall they have a poorer prognosis than other breast cancers. The main reason for this is the lack of a targeted treatment. However, new treatments are under study.
Clinical trials of treatments for triple negative breast cancer are underway. Promising new treatments (in combination with chemotherapy) include PARP inhibitors, bevacizumab and other targeted therapies.
Poly (ADP-ribose) polymerase (PARP) is an enzyme involved in DNA repair. Some chemotherapy drugs damage DNA. Adding a PARP inhibitor may lower the chances the cancer cells become resistant to the chemotherapy. When cancer cells become resistant to chemotherapy, the chemotherapy is no longer able to fight the cancer cells. So, by lowering the chances of resistance, the PARP inhibitor may increase the effectiveness of the chemotherapy.
The PARP inhibitor olaparib may benefit women with triple negative breast cancers who carry a BRCA1 or BRCA2 gene mutation.31 In one early study, iniparib (not a pure PARP inhibitor) seemed to benefit triple negative breast cancers, but this has not been confirmed in larger studies.32
Although these findings show promise for PARP inhibitors in the treatment of triple negative breast cancers, the studies included only a small number of women followed over a short time. And, studies suggest the potential benefit of PARP inhibitors may be limited to BRCA1- and BRCA2-related breast cancers. Larger, longer-term studies are underway to confirm these findings.
The genes linked to triple negative breast cancer are not well understood at this time. Thus, targeted therapies do not yet exist to treat these cancers. Potential targets for future therapies include the epidermal growth factor receptor (EGFR), aB-crystallin and cyclin E.33
Although the drug bevacizumab (Avastin) is no longer FDA-approved for the treatment of metastatic breast cancer, it is still under active study for the treatment of triple negative breast cancers.
Learn about Susan G. Komen for the Cure’s® work with the Triple Negative Breast Cancer Foundation (TNBC) and research we are funding to study triple negative breast cancer.
If you are newly diagnosed with breast cancer (triple negative or other type), we encourage you to consider joining a clinical trial. Talk to your health care provider or visit our clinical trial section for more information.
In collaboration with BreastCancerTrials.org we offer a custom matching service to help you find a clinical trial that fits your health needs. Learn more about this program.
According to Dr. Eric Winer, our chief scientific advisor, and director of the Breast Oncology Center and the Thompson Senior Investigator in Breast Cancer Research at Dana-Farber Cancer Institute and professor of medicine at Harvard Medical School, “At this time, triple negative breast cancer remains one of the most challenging subtypes of breast cancer. Treatment options are more limited than for other women with breast cancer, but triple negative disease is an area of very active research. Importantly, many women do well with our standard therapies and we anticipate great progress over the next decade.”
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Posted February 14, 2012