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Several tests might be done on breast biopsies or blood samples to diagnose breast cancer, help choose drugs to best treat your cancer, or monitor your cancer.

Why other tests might be done

Tests are often done to help:

• Diagnose breast cancer.
• Choose which treatments might work best for your cancer, sometimes called precision or personalized medicine.
• Monitor your health.

A pathologist, a doctor who specializes in diagnosing and classifying disease, will look at and test the samples to help your team diagnose and manage your breast cancer treatment. Some of these tests may take up to a few weeks for results.

If you have any questions about your pathology results or any diagnostic tests, talk to your doctor. If needed, you can have a second pathologist look at the samples and test results for a second opinion.

Tests to diagnose cancer and guide treatment

Lab tests might be done to get information about your cancer and how best to treat it. Most look at the cancer cells themselves, but some check your own cells for an inherited gene change you were born with. These tests, also known as biomarker tests, might be done on tissue taken during a biopsy, surgery, or blood draw.

HER2

All invasive breast cancers are tested for the HER2 protein to see if too much is being made. If it is not clear how much HER2 protein is present, other tests might be done to see if the cancer cells have extra copies of the HER2 gene. For more information, see Breast Cancer HER2 Status.

PD-L1

People with advanced or metastatic triple-negative breast cancer might have their cancer tissue tested for PD-L1, which can show if the cancer is more likely to respond to treatment with certain immunotherapies along with chemotherapy. 

Ki-67

The Ki-67 test estimates the rate of cell proliferation, or how quickly a cancer cell copies its DNA and divides into 2 cells. Faster division means the cancer is faster growing or more aggressive.

If the Ki-67 labeling index is high, it means that the cancer cells are dividing more rapidly. In early-stage breast cancers, Ki-67 testing might be used to help estimate outlook or recommend treatment.

The results of this test can vary depending on things like the lab doing the testing, the testing method, and what part of the tumor is tested. 

BRCA1 and BRCA2 gene changes

If you have an advanced HER2-negative breast cancer, your doctor might test you (not your cancer cells) for a hereditary BRCA1 or BRCA2 gene change (mutation). If you have one of these gene changes, treatment with the targeted drugs olaparib (Lynparza) or talazoparib (Talzenna) might be options.

PIK3CA, AKT1, and PTEN gene changes 

Certain changes in these 3 genes can help cancer cells grow. If you have advanced breast cancer that is hormone receptor-positive and HER2-negative, and if the cancer cells show changes in one of these genes, a targeted drug such as capivasertib (Truqap), alpelisib (Piqray), or inavolisib (Itovebi) might be an option, along with the hormone drug fulvestrant and possibly other medicines.

ESR1 gene changes

The ESR1 gene contains the instructions for the estrogen receptor (ER) protein. Changes in this gene can make breast cancers less likely to respond to some forms of hormone therapy.

For advanced breast cancers with these gene changes, a hormone drug such as elacestrant (Orserdu) or imlunestrant (Inluriyo) might be helpful. This gene change can be tested for in a sample of your blood.

NTRK gene changes

Some breast cancer cells might have changes in one of the NTRK genes, which can sometimes lead to cancer growth. The targeted drugs larotrectinib (Vitrakvi), repotrectinib (Augtyro), and entrectinib (Rozlytrek) might be options for people with advanced breast cancers with NTRK gene changes.

RET gene changes

Some breast cancer cells can have changes in the RET gene, which can cause them to grow abnormally. Targeted drugs like selpercatinib (Retevmo) can block the RET protein, stopping cancer growth.

MSI and MMR testing 

Breast cancer cells might be tested to see if they show high levels of gene changes called microsatellite instability (MSI). Testing might also be done to see if the cancer cells have changes in any of the mismatch repair (MMR) genes (MLH1, MSH2, MSH6, and PMS2). 

Breast cancer cells that have a high level of microsatellite instability (MSI-H) or a defect in a mismatch repair gene (dMMR) might be treated with the immunotherapies pembrolizumab (Keytruda) or dostarlimab (Jemperli).

Tumor mutational burden (TMB)

TMB is a measure of the number of gene changes inside cancer cells. Breast cancer cells that have many gene changes (a high TMB) might be more likely to respond to certain immunotherapies. If your breast cancer tissue is tested and found to have a high TMB (TMB-H), treatment with pembrolizumab (Keytruda) might be an option.

Circulating tumor DNA (ctDNA)

Tests for ctDNA look for the presence of small pieces of cancer DNA in the blood. This test can be used to monitor how well treatment is working or catch a recurrence before an imaging test might be able to see it.

Tests to monitor your health and cancer

Certain blood tests can help to get a sense of a person’s overall health. For example, they can be used to help determine if a person is healthy enough to have surgery or certain types of treatment.

A complete blood count (CBC) measures the levels of white blood cells, red blood cells, and platelets in your blood. This test can be used during treatment, such as chemotherapy, to check for possible problems or side effects.

This test can be used to check for:

• Anemia, or a low number of red blood cells
• Higher risk of bleeding due to a low number of blood platelets
• Higher risk of infections due to a low number of white blood cells

Blood chemistry tests can be used to measure how well your liver and kidneys are working, as well as the levels of certain minerals in your blood. This is often checked before surgery or taking certain chemotherapy, targeted therapy, and immunotherapy medicines.