Molecular Subtypes of Breast Cancer

Doctors have long recognized that breast cancers often behave differently (for example, how fast they grow or how likely they are to come back) in different people. As technology has advanced, so too have the ways that researchers can predict how specific breast cancers might behave.

A molecular subtype is a grouping of breast cancers that share characteristics, hormone receptor status, for example, that is commonly used in research. Understanding your molecular subtype may help inform your treatment. 

While the definitions continue to evolve, there are currently four main molecular subtypes of invasive breast cancer. 

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  luminal A

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  luminal B

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  HER2-enriched 

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  triple negative or basal like

While you may see terms such as estrogen receptor-positive or HER2-negative in your pathology report, molecular subtypes are unlikely to be mentioned. This is because molecular subtypes of breast cancer are mainly used by researchers in clinical trials. Researchers use molecular subtype information to create treatment standards of care and when developing new treatments.

Luminal A breast cancer is commonly called hormone receptor-positive, HER2-negative breast cancer. It is estrogen receptor-positive and progesterone receptor-positive, HER2-negative, and has low levels of the protein Ki-67, which helps control how fast cancer cells grow. Because it has low Ki-67 levels, luminal A cancers tend to grow more slowly than other subtypes, be lower grade, and respond well to treatment.

Luminal A is the most common molecular subtype of breast cancer, making up about 50% to 60% of all breast cancer cases. ¹

Common treatments for luminal A breast cancer are:

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  surgery

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  radiation therapy

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  hormonal therapy

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  chemotherapy in some cases

Luminal B breast cancer is also hormone receptor-positive and can be either HER2-positive or HER2-negative.

Luminal B breast cancers are positive for one of the hormone receptors: either estrogen or progesterone. In most cases, luminal B breast cancers are estrogen receptor-positive, but some are progesterone receptor-positive. This subtype of breast cancer has high levels of Ki-67, which means the cancer cells are growing faster than cancer cells with low levels of Ki-67.

Luminal B breast cancers are less common than luminal A, making up about 15% to 20% ² of breast cancer cases.

Compared with luminal A breast cancers, luminal B breast cancers ³:

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  are faster growing 

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  are higher grade 

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  are larger in size

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  are more aggressive

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  have lower levels of hormone receptors

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  are more likely to come back (recur)

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  have a poorer prognosis

Common treatments for luminal B breast cancer are:

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  surgery

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  radiation therapy

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  chemotherapy

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  targeted therapy, if the cancer is HER2-positive

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  hormonal therapy, though luminal B cancers are less likely to respond to hormonal therapy medicines than luminal A breast cancers

HER2-enriched breast cancers are commonly called HER2-positive. They may be hormone receptor-positive or hormone receptor-negative..

HER2-enriched breast cancers make up 10% to 15% ⁴ of breast cancer cases.

Compared to luminal A and luminal B cancers, HER2-enriched cancers tend to be:

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  faster growing 

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  more aggressive

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  higher grade

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  diagnosed at a later stage

Without treatment, HER2-enriched cancers have a worse prognosis than luminal cancers; however, there are multiple medicines that target HER2-positive cancers, including Herceptin (chemical name: trastuzumab) and Perjeta (chemical name: pertuzumab).

Common treatments for HER2-enriched breast cancer are:

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  surgery

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  radiation therapy

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  chemotherapy

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  targeted therapy

Triple-negative or basal-like breast cancer is estrogen receptor-negative, progesterone receptor-negative, and HER2-negative.

Triple-negative breast cancer is more common in:

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  people with a BRCA1 mutation

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  younger women

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  Black women

Worldwide, about 20% of all breast cancers are triple-negative. ⁵ According the the American Cancer Society, in the United States, triple-negative breast cancer represents 10% of breast cancers overall, but nearly 20% among Black women

Compared to luminal A, luminal B, and HER2-enriched breast cancer, triple-negative breast cancer is:

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  faster growing

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  higher grade

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  more aggressive

Because triple-negative breast cancer lacks receptors for estrogen, progesterone, and HER2, hormonal therapy medicines and anti-HER2 medicines aren’t effective treatments. Common treatments for triple-negative breast cancer are:

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  surgery

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  radiation therapy

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  chemotherapy

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  immunotherapy

 

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