Molecular Subtypes of Breast Cancer
How are molecular subtypes of breast cancer used?
Molecular subtypes of breast cancer are used mostly in research settings and are not part of a standard breast cancer diagnosis. So, the molecular subtype of your tumor is not part of your pathology report and is not used to guide your treatment.
Researchers are studying how molecular subtypes of breast cancer may be useful in planning treatment and developing new therapies.
Treatment decisions are guided mainly by tumor stage, tumor grade, hormone receptor status and HER2 status. These factors are also related to survival.
What are molecular subtypes of breast cancer?
The complex profile of each subtype is determined using molecular and genetic information from tumor cells.
Most studies divide breast cancer into 4 main molecular subtypes:
- Luminal A
- Luminal B
- Basal-like/triple negative
- HER2-enriched
These subtypes also appear in ductal carcinoma in situ (DCIS) [49].
There are many other less common molecular subtypes, including claudin-low and molecular apocrine types.
Luminal A
Luminal tumor cells look the most like cells of breast cancers that start in the inner (luminal) cells lining the mammary ducts.
Luminal A tumors tend to be:
- Estrogen receptor-positive (ER-positive)
- HER2-negative
- Tumor grade 1 or 2
About 40% of breast cancers are luminal A tumors [50-51].
Of the 4 main molecular subtypes, luminal A tumors tend to have the best prognosis, with fairly high survival rates and fairly low rates of breast cancer recurrence [50-53].
Luminal B
Luminal tumor cells look like the cells of breast cancers that start in the inner (luminal) lining the mammary ducts.
Luminal B tumors tend to be estrogen receptor-positive (ER-positive). They may be HER2-negative or HER2-positive.
Women with luminal B tumors are often diagnosed at a younger age than those with luminal A tumors [52,54].
Compared to luminal A tumors, luminal B tumors tend to have factors that lead to a poorer prognosis including [50-52]:
About 15% to 20% of breast cancers are luminal B tumors [50-51].
Women with luminal B tumors tend to have fairly high survival rates, although not as high as those with luminal A tumors [52-53].
Basal-like/triple negative
Basal-like tumors have cells that look similar to those of the outer (basal) cells surrounding the mammary ducts.
Triple negative breast cancer is:
- Estrogen receptor-negative (ER-negative)
- Progesterone receptor-negative (PR-negative)
- HER2-negative
Most triple negative tumors are basal-like.
About 15% to 20% of breast cancers are basal-like/triple negative [35,50-51,55].
These tumors tend to occur more often in [35,55-59]:
- Younger women
- Black and non-Hispanic Black women (more on race, ethnicity and subtypes of breast cancer)
- People with a BRCA1 inherited gene mutation (if you’re diagnosed with triple negative breast cancer, the National Comprehensive Cancer Network recommends you get genetic testing)
Triple negative tumors may also be more common among Hispanic women compared to non-Hispanic white women [55,60-61]].
Learn more about BRCA1 inherited gene mutations.
Survival
Basal-like/triple negative tumors are often aggressive and have a lower chance of survival compared to the ER-positive subtypes (luminal A and luminal B tumors) [35,51,53,62].
However, triple negative breast cancers can be treated effectively, and survival is improving with new treatments.
Learn more about triple negative breast cancer, including treatment and survival.
Learn about clinical trials for people with basal-like/triple negative breast cancers.
HER2-enriched
The molecular subtype HER2-enriched is not the same as HER2-positive and is not used to guide treatment.
Although most HER2-enriched tumors are HER2-positive (and named for this reason), many are HER2-negative [51].
HER2-enriched tumors tend to be [51-52]:
- Estrogen receptor-negative (ER-negative)
- Progesterone receptor-negative (PR-negative)
- Higher tumor grade
About 10% to 15% of breast cancers are HER2-enriched subtype [50-51].
Women with HER2-enriched tumors may be diagnosed at a younger age than those with luminal A tumors [52,54].
HER2-enriched breast cancers that are HER2-positive can be treated with HER2-targeted therapies such as trastuzumab (Herceptin) and pertuzumab (Perjeta).
Race, ethnicity and molecular subtypes of breast cancer
Prevalence
Prevalence shows the proportion of people who have a breast cancer (or other health condition) at a given point in time. The prevalence of some molecular subtypes of breast cancer differs by race and ethnicity.
Basal-like/triple negative tumors are more common among Black and non-Hispanic Black women (especially before menopause) compared to women of other ethnicities [35,55-56,59].
Triple negative tumors may also be more common among Hispanic women compared to non-Hispanic white women [55,60-61].
Luminal A tumors may be more common among white women compared to women of other ethnicities [56,63].
Although the reasons for these differences are not clear, some factors (such as breastfeeding) may play a role [61,64-65].
Learn more about race, ethnicity and breast cancer.
Learn more about race, ethnicity and risk factors for triple negative breast cancer.
Survival
Higher rates of basal-like/triple negative tumors may explain, to some degree, the poor prognosis (chance of survival) of breast cancers diagnosed in Black and non-Hispanic Black women [56,64,66-67,78-80].
Also, luminal A tumors, which have the best prognosis of the molecular subtypes, occur less often in Black women than in white women [56,63].
Learn about Susan G. Komen®’s work in advancing health equity.
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Susan G. Komen partnered with Charles River Associates to publish the report, Inequities in Care and Treatment for Triple Negative Breast Cancer Patients, on the barriers to the care and treatment of TNBC. Read the full report. |
Updated 03/06/25
This content is regularly reviewed by an expert panel including researchers, practicing clinicians and patient advocates.
