Although still in the early stage of research, molecular breast cancer subtypes may become useful in planning treatment and developing new therapies. Most studies divide breast cancer into four major molecular subtypes:
- Luminal A
- Luminal B
- Triple negative/basal-like
- HER2 type
These same subtypes also appear in ductal carcinoma in situ [35-36].
Other less common molecular subtypes have also been described including normal breast-like, apocrine molecular type and claudin-low type. Breast cancers that do not fall into any of these subtypes are often listed as unclassified.
Learn more about luminal A, luminal B and HER2 molecular subtypes.
Triple negative/basal-like breast cancer
Triple negative breast cancers are:
- Estrogen receptor-negative (ER-)
- Progesterone receptor-negative (PR-)
- HER2/neu-negative (HER2-)
Basal-like tumors have cells with features similar to those of the outer (basal) cells lining the mammary ducts. Basal-like tumors also tend to express HER1 and/or cytokeratin 5/6- proteins and many contain p53 mutations [27,45-46].
Most triple negative tumors are basal-like and most basal-like tumors are triple negative. However, not all triple negative tumors are basal-like and not all basal-like tumors are triple negative (as shown in the figure below).
About 14 to 20 percent of breast cancers are triple negative or basal-like [27,37-44]. These tumors tend to occur more often in younger women and African American women (more on race/ethnicity and subtypes of breast cancer) [27,40-43,46-48]. And, most BRCA1 breast cancers and many BRCA2 breast cancers are both triple negative and basal-like [46,49].
Triple negative/basal-like tumors are often aggressive and have a poorer prognosis compared to the estrogen receptor-positive subtypes (luminal A and luminal B tumors) [27,38,40,50].
Learn more about BRCA1 and BRCA2 mutations.
Treatment of triple negative/basal-like breast cancer
Triple negative/basal-like tumors are usually treated with some combination of surgery, radiation therapy and chemotherapy. These tumors cannot be treated with hormone therapies or trastuzumab (Herceptin) because they are hormone receptor-negative and HER2/neu-negative.
Learn more about breast cancer surgery.
Learn more about radiation therapy.
Learn more about chemotherapy.
Emerging areas in treating triple negative/basal-like breast cancer
The genes linked to basal-like tumors are not well understood at this time and thus, targeted therapies do not yet exist. However, potential targets for future therapies include the EGF receptor, aB-crystallin and cyclin E [51].
Clinical trials studying treatment options for triple negative/basal-like tumors are underway. Learn more about clinical trials.
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.
Race/ethnicity and triple negative/basal-like breast cancer
The prevalence rates of the four subtypes of breast cancer appear to differ by race. In studies of women in the United States and Britain, triple negative/basal-like tumors appear to be more common among black women, especially those who are premenopausal, compared to white women [27,41-42,48,53-55]. 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/basal-like tumors [41,44,56-59].
Higher rates of triple negative/basal-like tumors may explain, to some degree, the poor prognosis of breast cancers diagnosed in younger black women. Further, luminal A tumors, which have the best prognosis of the subtypes, occur less often among premenopausal African American women compared to postmenopausal African American women and compared to white women of either menopausal status [27].
Updated 10/20/11
