What is a breast cancer genomic test?
A breast cancer genomic test analyses the activity of certain genes within your tumour. It does not look at your own DNA: it looks at the DNA of the cancer cells, and only at a few dozen genes selected because they are linked to recurrence risk.
Here is the idea: not all breast cancers are alike, even when they share the same size and grade under the microscope. For some tumours, hormone therapy alone is sufficient to prevent recurrence. For others, adding chemotherapy provides a real survival benefit. These two profiles are sometimes indistinguishable on standard pathology — that is exactly where genomic tests come in.
The genomic test analyses tumour gene activity to predict its behaviour.
The genomic test brings the missing piece of information. It gives a numerical score that essentially says: "this is how likely your tumour is to come back if we only give hormone therapy". If the score is low, chemotherapy will bring little to nothing, and it can be skipped. If the score is high, it will bring real benefit and should be given.
Important — not to be confused: this test has nothing to do with the oncogenetics consultation. Oncogenetics looks for an inherited constitutional mutation (BRCA1, BRCA2, PALB2…) on a blood sample: it evaluates your and your family's risk of developing other cancers. The genomic test, on the other hand, is performed on the tumour itself and says nothing about heredity — it only predicts how this specific cancer will behave. Both can be offered in parallel, but they answer completely different questions.