How does a breast cancer gene expression test work?

The laboratory examines which genes in the tumour are more or less active. This pattern is combined into a report that supports decisions after surgery or biopsy in selected breast cancers. The result is one part of the picture: tumour size, grade, lymph-node findings, hormone receptors, HER2 status, health and personal preferences also matter.

The test describes the tumour’s biology; it is not an inherited test for cancer risk in relatives. It also does not replace the pathology report or show whether a breast lump is cancer.

Usually, the laboratory uses tissue already collected during a biopsy or operation, so another procedure may not be needed. The result is discussed with your oncology team, who can explain its category in the context of your diagnosis. Ask how the report would change the balance between endocrine treatment, chemotherapy, radiotherapy or observation, and whether the sample is suitable for testing.

Contact your breast-care team if you are waiting for a result and do not know when it will be reviewed, or if a treatment recommendation is unclear. Seek prompt assessment for a new breast change rather than waiting for gene expression testing, because the test is performed on cancer tissue and cannot diagnose a symptom by itself.

Ask whether this test applies to your tumour type, what the report can and cannot predict, how it interacts with your pathology findings, and what treatment choices would change for each possible result.