Oncotype Dx is an experimental test designed to help doctors to estimate how much benefit chemotherapy might offer to women with hormone sensitive (ER-positive) breast cancer that has not spread to the lymph nodes. It isn’t a suitable test for women with hormone insensitive (ER-negative) breast cancer or breast cancer that has spread to lymph nodes.

Because Oncotype Dx is relatively new it needs to be properly tested before we can know if it is reliable. A large study (TAILORx) is currently happening in the USA. The study is looking at how dependable the Oncotype test is and whether it could be used more widely. So at present the benefits of this test are not clear and its use is still experimental. Oncotype Dx is not available on the NHS.

For many women with hormone sensitive early breast cancer, that hasn’t spread to their lymph nodes, the outlook is very good and they can often be treated successfully with surgery, radiotherapy and hormone treatment. But, because in a few women the cancer may come back, chemotherapy might be offered too. However, as most women’s risk of cancer returning is low, deciding whether to have chemotherapy can be difficult, especially as it causes side-effects.

At the moment, the decision is usually based on factors that can influence the risk of breast cancer returning (recurrence). These include: a woman’s age, the grade of her cancer, her HER2 status, and any personal feelings she has about risk. If these factors clearly show a woman is in a higher or lower risk group the decision can be clear. But in some cases it is more difficult to judge whether or not chemotherapy may be worthwhile.

It is hoped that a more accurate way of measuring individual risk would make the decision easier and help women with a low risk of recurrence to avoid unnecessary chemotherapy. The Oncotype Dx test (and similar tests being developed) aim to help with this.

The Oncotype Dx test looks at changes to genes in breast cancer cells. These gene changes can affect how the cancer behaves. The types of gene changes looked at by the test are ones that happen during a person’s lifetime (and aren’t inherited from a parent or passed onto children).

Many different types of changes can occur in the genes of breast cancer cells. Researchers are still trying to identify the most important ones and understand how they affect the cancer. Oncotype Dx tests for 16 breast cancer-related genes that can influence how a breast cancer behaves. The test measures the number and pattern of these gene changes in a breast tumour sample to give a score. The score aims to predict how likely it is that a breast cancer will come back in the future and is called the “recurrence score” (RS). From this score an individual woman would be said to have either a low, intermediate or high risk of breast cancer returning.

The main purpose of the test would be to help a woman decide whether her risk of recurrence is low enough for her to choose not to take chemotherapy. If a woman was sure she want to have chemotherapy anyway – no matter what risk group she was in then there would be no point in taking the test.

At present the Oncotype Dx test has only been used to try to predict the benefits of taking chemotherapy followed by tamoxifen compared to tamoxifen alone. It hasn’t been tested on women being treated with a type of hormonal therapy drug called an aromatase inhibitor so can’t predict how helpful chemotherapy might be for them.

Other tests based on the same principles as Oncotype Dx - but looking at different patterns of genes - are also being developed. It is hoped that in the future one or a combination of these tests will help women with breast cancer, and their doctors, to plan the best treatment for them.

Reference

• Paik S et al A multigene assay to predict recurrence of tamoxifen-treated, node-negative breast cancer. N Engl J Med 2004 Dec 30;351(27):2817-26.