After a biopsy or surgery to remove breast tissue, a sample of cells is sent to the laboratory. A doctor called a pathologist does various tests on the cells. This can diagnose cancer and also show which type of cancer it is.
Some tests can also show how well particular treatments might work, such as hormone therapies or targeted cancer drugs.
Finding the type of cancer
A pathologist looks at the cancer cells under a microscope to see which type of breast cancer it is. They can tell this by the shape of the cells and the pattern of the cells in the breast tissue.
Pathologists also sometimes use particular dyes to stain the cells and show up certain proteins or features of the cells.
Hormone receptor tests
Breast cancers can have receptors for the female hormones, oestrogen and progesterone.
Cancers that have receptors for oestrogen are called oestrogen receptor positive or ER positive (ER+) breast cancer. About 75 out of every 100 breast cancers (about 75%) are oestrogen receptor positive.
Oestrogen receptor negative or ER negative (ER-) breast cancers have very low levels of oestrogen receptors or no oestrogen receptors.
Hormone therapies can work very well for cancers that are oestrogen receptor positive. They stop oestrogen from stimulating the cancer cells to grow and divide.
Some breast cancers also have receptors for progesterone. They are called progesterone receptor positive or PR positive.
Examples of hormone therapy drugs include tamoxifen and letrozole.
Proteins for targeted cancer drugs
Testing cancer cells for particular proteins can help to show whether targeted drug treatments might work for your breast cancer.
Targeted cancer drugs are treatments that change the way cells work and help the body to control the growth of cancer.
Some breast cancers have large amounts of a protein called HER2 receptor (human epidermal growth factor 2 receptor). They are called HER2 positive breast cancers. About 15 out of every 100 women (around 15%) with early breast cancer have HER2 positive cancer.
Targeted cancer drugs such as trastuzumab (Herceptin) can work well for this type of breast cancer. These drugs attach to the HER2 protein and stop the cells growing and dividing.
Triple negative breast cancer
Triple negative breast cancers don't have oestrogen receptors, progesterone receptors or HER2 receptors. Around 15 out of 100 women have this type (around 15%). It is more common in younger women.
Hormone therapies and targeted cancer drugs do not work well for this type of breast cancer. So you are more likely to have chemotherapy.
Tumour profiling tests
Tumour profiling tests are also called gene expression profiling tests (GEP tests) or gene assays. They look at groups of cancer genes to find out how active they are.
The activity of particular genes helps doctors predict whether a cancer is likely to come back.
Doctors can use a computer online tool to help them decide the best treatment for you after surgery for early breast cancer. One possible treatment is chemotherapy, but it is not always clear if chemotherapy is needed. In this situation doctors use tumour profiling tests to get more information. This helps them to decide who needs extra treatment with chemotherapy to lower the risk of the cancer coming back.
Tumour profiling tests are available for breast cancer. Your doctor can explain whether this testing is an option for you. Examples include EndoPredict (EPclin score), Oncotype DX Breast Recurrence Score and Prosigna.
These tests should not be confused with tests that look for an inherited faulty gene that increases a person’s risk of getting breast cancer in the first place.