The PIK3CA mutation, and why it may matter for your cancer care

Knowing what type of metastatic breast cancer (MBC) you have and what causes your cancer to grow is important. If you’re living with MBC, you may already know your MBC type, often defined by your tumor's hormone receptor (HR+/-, also known as ER+/- or PR+/-) and HER2 protein (HER2+/-) status. But it’s also important to know whether your cancer has a mutation, such as PIK3CA.

Like your HR and HER2 status, your tumor’s PIK3CA mutation status may affect your cancer care.

Breast Cancer Types

Click on your type below to learn about the hormones, proteins and mutations that make it grow.

Types of Metastatic Breast Cancer

The PIK3CA gene is the most commonly mutated gene in HR+/HER2- breast cancer, affecting about 40% of people with this type. It's important to know if you have a PIK3CA mutation, as it can affect how your cancer progresses.


HR+/HER2- breast cancer is the most common form of breast cancer. In this cancer, hormones estrogen and progesterone cause the cancer to grow. There are also certain mutations that could impact your cancer and treatment options, such as if you have the PIK3CA mutation.


HR+/HER2+ is fueled by estrogen or progesterone hormones, as well as the HER2 protein.


HR-/HER2- breast cancer, commonly referred to as triple negative breast cancer (TNBC) is not fueled by estrogen, progesterone or the HER2 protein. Research shows that this type is most common in younger women, African American women and women who have the BRCA1 mutation.


HR-/HER2+ breast cancer has a mutation in the HER gene causing excess HER protein, which makes the cancer grow. HR-/HER2+ breast cancer commonly has the characteristics of inflammatory breast cancer (IBC). IBC typically develops from cells that line the milk ducts of the breast and then spread beyond the ducts. IBC is often initially diagnosed as advanced. IBC is not always HR-/HER2+, so talking to your doctor about your type of breast cancer is still recommended.

Understanding PIK3CA, and what it means for you

What is a PIK3CA mutation in metastatic breast cancer?

What it is

Mutations such as BRCA1/2 can be inherited or passed from parent to child. However, PIK3CA mutations are not inherited, but may occur sporadically. The PIK3CA gene is the most commonly mutated gene in HR+/HER2- breast cancer, affecting about 40% of people with that subtype.2 PIK3CA mutations have been linked to cancer growth.3

Why knowing your PIK3CA status matters

Why it matters

Just as your tumor’s HR and HER2 status inform your doctor whether certain proteins fuel your cancer, your tumor’s mutation status tells your doctor whether a gene mutation may be contributing to the growth of your cancer.

Your tumor’s mutation status may affect how your doctor manages your cancer care.
Identifying a PIK3CA gene mutation

What you can do

Talk to your doctor about how you can find out your tumor’s mutation status.

Identifying the PIK3CA mutation can help your doctor understand your disease better and plan your personalized care.
Questions to ask your doctor include
Questions you might want to ask your doctor include:
  • How do I know my tumor has a mutation?
  • At what stage in my patient journey is it appropriate to test for mutations?
  • How long will it take to receive results from a mutation test?
  • How does having a mutation like PIK3CA or BRCA1/2 impact my cancer care?

Let’s talk more about mutations in MBC.

What is a mutation?

Mutations are like typos in your DNA

In cancer, mutations may affect how the tumor grows, leading to flawed or different instructions for a given cell.

What are the types of mutations?

Sporadic mutations

Sporadic Mutations:

occurs at random and is not passed down from parent to child. PIK3CA is a sporadic mutation.5

Genetic mutations

Inherited Mutations:

passed down from parent to child. BRCA1/2 is an inherited mutation.1

MBC Mutation Myth vs Fact
  • MYTH

    I already know my MBC type – I do not need to know anything else about my cancer.


    There may be mutations called PIK3CA or BRCA1/2 in your tumor that could impact your cancer care. Talk to your doctor to learn more about your tumor’s mutation status.

  • MYTH

    All MBC mutations are passed down from parent to child.


    The PIK3CA mutation is not inherited, which means your tumor may have it regardless of your family history.

  • MYTH

    Mutations in cancer do not affect course of disease (or disease prognosis).


    Biomarkers and mutations, such as PIK3CA, have been linked to cancer growth, and may be associated with poorer prognosis.3,4

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  1. American Cancer Society. Breast Cancer Facts & Figures. 2018-2019. Available at:
  2. Sabine V, Crozier C, Brookes C, et al. Mutational analysis of PI3K/AKT signaling pathway in tamoxifen exemestane adjuvant multinational pathology study. Journal of Clinical Oncology. 2014;32:2951-2958.
  3. Miller TW, Rexer BN, Garrett JT, et al. Mutations in the Phosphatidylinositol 3-Kinase Pathway: Role in Tumor Progression and Therapeutic Implications in Breast Cancer. Breast Cancer Res. 2011.
  4. Saal LH, Johansson P, Holm K. Poor prognosis in carcinoma is associated with a gene expression signature of aberrant PTEN tumor suppressor pathway activity. PNAS. 2007;104(18):7564-7569.
  5. Sporadic Cancer: NCI Dictionary of Genetics Terms. Accessed October 28, 2019.