What is Molecular Subtyping of Breast Cancer and Why is It Important?

5 min read

What is Molecular Subtyping of Breast Cancer and Why is It Important?

When breast cancer is suspected, many different tests will be performed to confirm the diagnosis and determine the exact type of cancer. Because breast cancer diagnoses can vary so much, it is important for your doctor to gather as much information as possible in order to recommend the best treatment approach. 

There are many different types and subtypes of breast cancer. Your doctor will use breast cancer subtype information to help them choose the best treatment approach and give the most accurate prediction of survival and recovery. One method of subtyping breast cancer involves molecular classification or molecular subtypes. 

This article will break down the different molecular subtypes of breast cancer and share more about how they can help guide treatment. 

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What is Molecular Subtyping in Breast Cancer?

Molecular subtypes of breast cancer classify breast cancer based on several factors, including the type and behavior of the cancer cells, the hormone receptors on the cancer cells, and any other types of proteins involved in each cancer. 

By determining your breast cancer's molecular subtypes, your doctor can recommend a targeted and personalized treatment approach. The more information your doctor has about your breast cancer type, the higher the likelihood of a successful treatment. Certain cancer drugs are designed to target specific types of cancer cells. 

Different Types of Molecular Subtypes for Breast Cancer

There are four main types of molecular subtypes of breast cancer, including:

  • Luminal A
  • Luminal B
  • Triple-negative
  • HER2-positive

Luminal A

You may also hear of luminal A breast cancer, referred to as HR+/HER2-. This subtype of breast cancer is one of the most common molecular subtypes. Luminal A breast cancer will be estrogen receptor-positive and progesterone receptor-positive, meaning that the hormones estrogen and progesterone feed the cancer growth. 

Usually, treatment for luminal A breast cancer will involve drugs that lower amounts of progesterone and estrogen to help slow cancer growth. This type of cancer is typically slower growing and usually has a good prognosis.

Luminal B

Luminal B breast cancer is HR+/HER2+, meaning that people who have this type of breast cancer usually have abnormally high levels of the protein HER2. Luminal B breast cancer is associated with a poorer prognosis than luminal A because the tumor size is usually larger, the tumor grade is usually more advanced, and lymph node involvement is more common. This is sometimes referred to as triple-positive breast cancer.

Even so, luminal B breast cancer is still associated with a fairly high survival rate. Common treatment options for luminal B breast cancer include targeted therapy, biotherapy, or monoclonal antibody therapy. 


HER2-enriched breast cancer is not the same as HER2-positive. Although many HER2-enriched breast cancer tumors are HER2-positive, not all of them are. HER2-enriched breast cancer tumors are usually estrogen receptor-negative and progesterone receptor-negative. This type of breast cancer is usually treated using HER2-targeted therapies such as pertuzumab (Perjeta) and trastuzumab (Herceptin).

Triple-Negative Breast Cancer (TNBC)

Triple-negative breast cancer (TNBC) does not contain receptors for estrogen, progesterone, or HER2. This is one of the more invasive types of breast cancer, and it usually starts in the ducts of the breasts. Because this type of breast cancer does not contain receptors for estrogen, progesterone, or HER2, it cannot be treated with the same hormone therapies that target these hormones, as some of the other subtypes can. There are some other treatment options, such as chemotherapy and radiation therapy. 


Basal-like breast cancers are similar to triple-negative since they also usually do not have receptors for estrogen, progesterone, and HER2. However, basal-like and triple-negative are not the same. Basal-like breast cancer cells have differences in their proteins that triple-negative cancers do not have. 

Basal-like breast cancers are more often found in women who are younger and those who are of African descent. Basal-like breast cancers are often treated using surgery, radiation therapy, chemotherapy, and immunotherapy. 

How is Molecular Subtyping Used for Breast Cancer Treatment?

Treatment for breast cancer will vary from person to person. Your oncologist will consider a variety of important factors to help determine the best treatment approach for you. Molecular subtyping is one important method to help pinpoint the exact type of breast cancer you have and the best approach to take in treating it. 

Molecular subtypes help your doctor see what (if any) specific hormones and/or proteins fuel the growth of your cancer, which can allow them to use treatment approaches that target these. Molecular subtyping helps your doctor determine if you’re a good candidate for hormone therapy, which blocks certain hormones to treat cancer. 

Targeted Therapies for Breast Cancer

Some examples of targeted therapies that are used for treating breast cancer include:

  • Trastuzumab (Herceptin)
  • Pertuzumab (Perjeta)
  • Everolimus (Afinitor)

Treatment for Breast Cancer by Subtype

Common treatment approaches for breast cancer by subtype are listed below.

  • Luminal A breast cancer is often treated with hormone therapies to block hormones and stop the cancer from growing. Surgery may also be used as well to remove the tumor.
  • Luminal B breast cancer may be treated using chemotherapy or therapies that target the HER2 protein.
  • Triple-negative breast cancer may be treated with surgery if the cancer has not spread. Chemotherapy and radiation therapy may also be used. If the cancer has advanced, then your doctor may recommend PARP inhibitors, platinum chemotherapy, or immunotherapy. Hormone therapy is not used for this type of cancer since the cells do not react to estrogen, progesterone, or HER2. 
  • HER2-positive breast cancer is treated with therapies that target the HER2 protein, such as monoclonal antibodies. Monoclonal antibodies are designed to attack HER2 cells to stop their growth. These treatments may be given alone or in combination with chemotherapy. 

Survival Rates and Long-Term Planning

It is important to be aware of breast cancer molecular subtypes because it can help with determining the prognosis of your cancer (or the likelihood of a successful treatment). Some breast cancer types are less serious and easier to treat than others. For example, Luminal A is usually fairly easy to treat and is associated with higher survival rates. Triple-negative breast cancer is usually more aggressive and is often harder to treat. 

There are many different types and subtypes of breast cancer. Molecular subtyping is one of the ways oncologists evaluate breast cancers so they can direct their treatment plan in the direction that is most likely to work best. 

Personalized Breast Cancer Treatment in Colorado

At Rocky Mountain Breast Specialists, our oncologists use advanced and personalized approaches to treat cancer, including breast cancer. By understanding the exact molecular subtype along with other important factors, our experts are able to target specific cell characteristics to provide an effective treatment approach and a more accurate prognosis. 

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