Genomic Assays: Oncotype DX and MammaPrint

A genomic assay is a type of test that uses a sample of the breast cancer tissue to analyze the activity of a group of genes, rather than just a single gene. Genes contain the recipes for the various proteins a cell needs to stay healthy and function normally. Knowing whether certain genes are present or absent, overly active or not active enough, can help doctors predict the risk of the breast cancer returning later. This can be helpful in making treatment decisions, such as whether or not chemotherapy should be part of the treatment plan.

Two genomic assays are currently in use for breast cancer: Oncotype DX and MammaPrint. Oncotype DX looks at the activity of 21 genes, MammaPrint at 70 genes. Doctors do not automatically order one of these tests for every person with breast cancer. Instead, they typically reserve these tests for patients who (1) have early-stage breast cancer that has not traveled to the lymph nodes, or to just a few; and (2) in the case of Oncotype DX, hormone-receptor-positive breast cancer that can be treated with hormonal therapy. If you fit these criteria, you and your doctor can determine whether genomic testing is right for you. Genomic testing can be done as part of the initial pathology testing, or as a separate test ordered days, weeks, or even months later on the original tissue sample.

If you have the Oncotype DX test, your results are reported as a recurrence score number:

• Recurrence score lower than 18: This suggests you have a low risk of recurrence. The benefit of chemotherapy is likely to be small and will not outweigh the risks of side effects.
• Recurrence score between 18 and 31: This score suggests you have an “intermediate” risk of recurrence. It’s unclear whether the benefits of chemotherapy outweigh the risks of side effects.
• Recurrence score greater than 31: You have a high risk of recurrence, and the benefits of chemotherapy are likely to be greater than the risks of side effects.

Your report will tell you how greatly adding chemotherapy to your treatment plan can decrease the risk of distant recurrence (the breast cancer returning outside the breast) at 10 years. As part of its analysis, the Oncotype DX test also looks at the expression of hormone receptor genes — both the estrogen receptor (ER) and progesterone receptor (PR). So your report will include another score that indicates just how positive (or negative) the cancer cells test for estrogen receptors and progesterone receptors. This can be helpful in assessing how effective hormonal therapy is likely to be against the cancer.

If you have the MammaPrint test, your results are reported as either a low-risk or high-risk recurrence score:

• A low-risk score means that the cancer has a 10% risk of coming back within 10 years without any additional treatments after surgery.
• A high-risk score means that the cancer has a 29% risk of coming back within 10 years without any additional treatments after surgery.

Whichever test you have, you and your doctor will consider your scores in combination with the other information in your pathology report, such as the size and grade of the cancer, to come up with a treatment plan for you.

Learn more about Oncotype DX.

Learn more about MammaPrint.