The Who, What, Where, When and Sometimes, Why.

Tumor Characteristics

Hormone receptor status

Some breast cancer cells need estrogen and/or progesterone (hormones produced in the body) to grow. These cancer cells have special proteins inside, called hormone receptors.

When hormones attach to hormone receptors, the cancer cells with these receptors grow.

A pathologist determines the hormone receptor status by testing the tumor tissue removed during a biopsy.

  • Hormone receptor-positive tumors are estrogen receptor-positive (ER-positive) and progesterone receptor-positive (PR-positive). These tumors express (have a lot of) hormone receptors.
  • Hormone receptor-negative tumors are estrogen receptor-negative (ER-negative) and progesterone receptor-negative (PR- negative). These tumors do not express (have few or no) hormone receptors.

Most (about 70-80 percent) breast cancers are hormone receptor-positive [20,40].

Hormone receptor status is part of breast cancer staging and helps guide your treatment. 

Learn about hormone receptor status information on a pathology report.

Hormone receptor status and hormone therapy

Hormone receptor-positive breast cancers can be treated with hormone therapy drugs. These include tamoxifen and the aromatase inhibitors, anastrozole (Arimidex), letrozole (Femara) and exemestane (Aromasin). Ovarian suppression, with surgery or drug therapies, is also a hormone therapy.

Hormone receptor-negative breast cancers are not treated with hormone therapies because they don’t have hormone receptors.

Learn about hormone therapy for the treatment of early and locally advanced breast cancers.  

Learn about hormone therapy for the treatment of metastatic breast cancers.

Estrogen receptor status and progesterone receptor status

Breast cancers that are ER-positive tend to be PR-positive. And, cancers that are ER-negative tend to be PR-negative.

Sometimes, a breast cancer is ER-positive, but PR-negative. Because current hormone therapies are designed to treat ER-positive cancers, these cases are treated the same as breast cancers that are positive for both hormone receptors.

How do hormone therapies work?

Hormone therapies slow or stop the growth of hormone receptor-positive tumors by preventing the cancer cells from getting the hormones they need to grow.

They do this in a few ways:

  • Some hormone therapies, like tamoxifen, attach to the receptor in the cancer cell and block estrogen from attaching to the receptor.
  • Some hormone therapies, like aromatase inhibitors and ovarian suppression, lower the level of estrogen in the body so the cancer cells can’t get the estrogen they need to grow.

Hormone receptor status and prognosis

Hormone receptor status is related to the risk of breast cancer recurrence.

Hormone receptor-positive tumors have a slightly lower risk of breast cancer recurrence than hormone receptor-negative tumors in the first 5 years after diagnosis [13].

After 5 years, this difference begins to decrease and eventually goes away [13].


For a summary of research studies on hormone receptor status and survival, visit the Breast Cancer Research Studies section.  

HER2 status

HER2 (human epidermal growth factor receptor 2) is a protein that appears on the surface of some breast cancer cells. It may also be called HER2/neu or ErbB2.

The HER2 protein is an important part of the pathway for cell growth and survival.

  • HER2-positive breast cancers have a lot of HER2 protein. You also may hear the term HER2 over-expression.
  • HER2-negative breast cancers have little or no HER2 protein.

About 10-20 percent of newly diagnosed breast cancers are HER2-positive [20,41].

HER2 status is part of breast cancer staging and helps guide your treatment.

Learn about HER2 status information on a pathology report.

Testing for HER2 status

All tumors should be tested for HER2 status.

The main tests for HER2 status are:

  • Immunohistochemistry (IHC), which detects the number of HER2 protein receptors on the cancer cells
  • Fluorescence in situ hybridization (FISH), which detects the number of HER2 genes in the cancer cells

HER2-positive cancers and HER2-targeted therapies

HER2-positive breast cancers can benefit from HER2-targeted therapies, such as trastuzumab (Herceptin), which directly target the HER2 receptor [13].

Trastuzumab and other HER2-targeted therapies are not used for HER2-negative cancers.

Learn about HER2-targeted therapies in the treatment of early and locally advanced breast cancer.

Learn about emerging therapies for HER2-positive early and locally advanced breast cancer.

Learn about HER2-targeted therapies in the treatment of metastatic breast cancer.

Learn about emerging therapies for HER2-positive metastatic breast cancer.  

Proliferation rate

The proliferation rate is the percentage of cancer cells actively dividing.

In general, the higher the proliferation rate, the more aggressive the tumor tends to be and the more likely it is to spread to other parts of the body.

Tumors with a high proliferation rate (those that are growing fast) often have a poorer prognosis than those with a low proliferation rate.

Proliferation rate could be a good predictor of prognosis and whether or not a tumor will respond to chemotherapy. However, there are issues related to the measurement of proliferation rate.

Some medical centers assess proliferation rate, but it’s not standard. Proliferation rate is not routinely used by all health care providers to guide treatment.


The Ki-67 test is a common way to measure proliferation rate. When cells are growing and dividing (proliferating), they make proteins called proliferation antigens. Ki-67 is a proliferation antigen.

The result of this test is reported as the percentage of tumor cells with Ki-67 antigen. The higher the percentage, the more aggressive the tumor tends to be.

Learn about proliferation rate information (including Ki-67 test results) on a pathology report.



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