Triple-positive breast cancer is a type of breast cancer that tests positive for estrogen receptors, progesterone receptors, and high levels of HER2 protein.

Some types of breast cancer cells use estrogen and progesterone as well as a protein called HER2 to grow.

Knowing whether cancer cells have estrogen or progesterone receptors, and the level of HER2 protein, can help determine the best course of treatment.

This article looks at the diagnosis and treatment for triple-positive breast cancer, and the outlook for people diagnosed with this type of cancer.

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Triple-positive breast cancer is a type of breast cancer. It has cancer cells that test positive for the following three features:

  • estrogen receptors
  • progesterone receptors
  • a larger amount of human epidermal growth factor receptor-2 (HER2) protein

These features mean that treating triple-positive breast cancer can involve using hormone therapy and drugs to target hormone receptors and HER2.

Around 10% of all breast cancers are hormone receptor-positive and HER2-positive.

Estrogen and progesterone receptors

Estrogen and progesterone receptors are proteins in cells that attach to the hormones estrogen and progesterone to allow the cells to grow. Normal breast cells have these receptors.

Some breast cancer cells also have estrogen and progesterone receptors. This means the cancer cells can attach to the hormones to grow.

If breast cancer cells have estrogen receptors, they are ER-positive. If they have progesterone receptors, they are PR-positive.

One or both of these receptors means the breast cancer is hormone-receptor positive. Hormone therapy drugs can help prevent estrogen and progesterone attaching to the receptors to stop the cancer growth.

HER2 protein

HER2 is a protein that allows breast cancer cells to grow quickly. If breast cancer has a higher amount of HER2 than usual, the breast cancer is HER2-positive.

To diagnose triple-positive breast cancer, doctors will test a biopsy sample for hormone receptors and HER2 levels.

A doctor may use an immunohistochemistry (IHC) test to check cancer cells for estrogen and progesterone receptors.

An IHC test uses antibodies to see if they attach to certain substances in cancer cells. An IHC test can find out if cancer cells have hormone receptors or high levels of HER2.

A doctor may also use a fluorescence in situ hybridization (FISH) test to check HER2 levels in cancer cells.

A FISH test uses specialized fluorescent dye and DNA to show changes in chromosomes and can also show levels of the HER2 gene.

Treating triple-positive breast cancer may include using a combination of treatment methods, which may vary for each individual case.

Most people with breast cancer will have surgery to remove as much of the cancer as possible. This may include partial or total breast removal.

People may have additional treatments to shrink a tumor before surgery or destroy any remaining cancer cells after surgery. This may include:

According to a 2018 article, treating triple-positive breast cancer may include using hormone therapy to target hormone receptors, either on its own or alongside drugs to target HER2.

The type of hormone therapy may depend on whether people have gone through menopause. In people who are premenopausal, treatments may include:

  • oophorectomy, to surgically remove the ovaries
  • gonadotropin-releasing hormone agonists, to temporarily prevent the ovaries from producing estrogen
  • medications, such as tamoxifen

Tamoxifen attaches to the hormone receptors in the breast cancer cells, stopping them from accessing the hormones they need to multiply.

In people who are postmenopausal, treatments may include:

  • aromatase inhibitors to block the enzyme aromatase, which converts other hormones, such as letrozole, anastrozole, or exemestane, into estrogen
  • tamoxifen combined with fulvestrant, a selective estrogen receptor degrader (SERD)

Treatments to target HER2 may include:

  • monoclonal antibody drugs, such as trastuzumab or pertuzumab
  • combining trastuzumab and pertuzumab alongside chemotherapy, which may be more effective than only one of the drugs with chemotherapy
  • targeted therapy with tyrosine kinase inhibitors, such as lapatinib or neratinib, possibly in combination with trastuzumab
  • antibody-drug conjugates, such as trastuzumab emtansine (T-DM1)

CDK4/6 inhibitors are a more recent treatment option to prevent cancer cell growth and include the drugs palbociclib, ribociclib, and abemaciclib. People may have CDK4/6 inhibitors in combination with hormone therapy to treat triple-positive breast cancer.

People may also want to speak with a healthcare professional about taking part in clinical trials that are currently exploring new breast cancer treatments.

The outlook for a person with triple-positive breast cancer may depend on many different factors, including:

  • the stage of cancer
  • tumor size and grade
  • how fast the cancer is growing
  • the location of the cancer and if it has spread
  • if the cancer is likely to return
  • a person’s age and overall health
  • whether a person has gone through menopause or not
  • whether it is a recent diagnosis or if the cancer is recurring

HER2-positive breast cancer may be more likely to grow and spread more quickly than HER2-negative breast cancers. However, HER2-positive breast cancers are far more likely to respond to treatments that target the HER2 protein.

According to a 2021 article, treatment with trastuzumab and pertuzumab may improve the outcome for HER2-positive breast cancers. Advances in anti-HER2 treatments have resulted in significant outlook improvements for people with HER2-positive breast cancer.

The research also suggests 5–10 years of hormone therapy treatment for hormone receptor-positive breast cancer may significantly improve survival rates.

Hormone receptor-positive breast cancer may grow more slowly than hormone receptor-negative breast cancers. People with hormone receptor-positive breast cancer may have a better short-term outlook, although there is the possibility that the cancer will return after treatment.

Triple-positive breast cancer means the breast cancer cells test positive for estrogen receptors, progesterone receptors, and have higher than usual levels of HER2 protein.

This means that hormone therapy and drugs targeting HER2 may help treat triple-positive breast cancer. Other treatments may include surgery, chemotherapy, and radiation therapy.

The outlook for people with triple-positive breast cancer may depend on various factors, including stage of cancer, how the cancer responds to treatment, and a person’s age and overall health.