Tests for Breast Cancer

Breast cancer is a serious condition that requires accurate diagnosis. Laboratory tests play a crucial role in this process. If you have been diagnosed with breast cancer, you will likely have done some of these tests through blood samples or a breast biopsy. Understanding these tests and their results is vital for effective communication between you and your doctor. Knowing the implications of your tests can help you make informed decisions about your treatment options and manage your expectations throughout the recovery process.

Blood tests alone are not typically used to diagnose breast cancer. However, there are specific blood tests that can be helpful in assessing certain aspects of breast cancer, such as monitoring treatment response or identifying specific markers associated with the disease. Here are some blood tests associated with breast cancer.

Complete Blood Count (CBC)

A CBC measures the levels of different types of blood cells, including red blood cells, white blood cells, and platelets, in your blood. Abnormalities in these counts indicate your suitability for certain cancer treatments.

Comprehensive Metabolic Panel (CMP)

This test evaluates the levels of various chemicals in the blood, including glucose, electrolytes, and liver enzymes. It provides information about the overall health of organs like the liver and kidneys, which can be affected by cancer. This information will not only indicate if cancer has spread to certain organs, such as the liver or bones but also determine what treatment drugs can be used.

Tumor Markers

Tumor markers are substances produced by cancer cells or other cells in the body in response to cancer. These substances can be found in the blood. In breast cancer, some common tumor markers include:

• Carcinoembryonic antigen (CEA)

Elevated levels of this protein may suggest breast cancer, but this marker is not specific to breast cancer and can be elevated in other conditions, such as colorectal cancer. Low or decreasing levels may indicate a response to cancer treatment.

• Cancer antigen 15-3 (CA 15-3)

Elevated levels of this protein may suggest breast cancer, but this marker is not specific to breast cancer and can be elevated in other conditions.

• Cancer antigen 27-29 (CA 27-29)

Similar to CA 15-3, this protein may be elevated in breast cancer, but it's not exclusive to this type.

• Circulating Tumor Cells (CTCs)

CTCs are cancer cells that have detached from the primary tumor and are circulating in the bloodstream. Tests that detect and analyze CTCs can provide information about disease progression and treatment response.

When a sample is taken from a breast tumor through a biopsy or surgery, it undergoes pathologic examination. The pathologist determines:

• The histological type of breast cancer.
• The size of the tumor.
• The grade of the tumor.
• Whether the tumor has spread to the axillary lymph nodes.
• Whether the tumor has been completely excised.

In addition, the breast cancer tissue is tested for several proteins and sometimes, genes. This information will help determine the specific subtype of breast cancer you have, the prognosis and what treatment strategy will be most suitable for you. The breast cancer cells will be tested for the following proteins.

Hormone receptor proteins

All breast cancers will be tested for hormone receptors, specifically estrogen receptors (ER) and progesterone receptors (PR). Testing is normally done by immunohistochemistry (IHC). Breast cancers that are hormone receptor-positive often respond to hormone therapy.

Human epidermal growth factor receptor 2 protein (HER2)

This test determines whether the HER2 oncoprotein is overexpressed in breast cancer cells. In addition to immunohistochemistry, a fluorescence in situ hybridization (FISH) assay may be performed. HER2-positive breast cancers can be treated with targeted anti-HER2 therapy.

PD-L1 protein

If you have metastatic triple-negative breast cancer, your breast cancer tissue may be tested for the PD-L1 protein. PD-L1 is a protein that regulates the immune response to cancer cells. Cancers that express PD-L1 may be treated with immunotherapy, especially for cancers that are aggressive and difficult to treat, such as triple-negative breast cancer.

Ki-67 Index

This is a marker of cell proliferation and can be assessed by immunohistochemistry. It helps predict how aggressively the cancer is likely to behave. It is not a routinely used prognosis parameter.

Several assays measure the expression levels of multiple cancer genes in breast tumors. The two major utilities of these assays are (a) long-term prognosis and (b) predicting whether a given tumor may benefit from adjuvant chemotherapy.

Genetic testing for breast cancer involves analyzing specific genes to identify mutations or alterations. Besides identifying gene mutations to check one’s risk of developing breast cancer, your doctor may need to look for specific gene alterations that may indicate the suitability of certain treatments. The two most well-known genes associated with hereditary breast cancer are BRCA1 and BRCA2. However, your doctor may also look for changes in other genes, such as PIK3CA and ESR1.

Remember, the recommended tests will depend on the individual's clinical presentation, pathology results, and treatment plan. It's crucial to discuss with a healthcare provider or an oncologist who can guide you through the appropriate tests based on your specific situation.