Purpose: The clinical and economic data for the two currently available gene-expression assays are reviewed.
Summary: Two gene-expression assays, used to determine the risk of breast cancer recurrence in patients with stage I or II node-negative breast cancer, are currently available. Oncotype DX is an assay performed on RNA extracted from paraffin-embedded tumor tissue. It analyzes the expression of 21 genes: 16 cancer-related genes and 5 reference genes. The results are used to calculate a recurrence score to identify the likelihood of cancer recurrence in patients treated with tamoxifen. The results of two studies evaluating the ability of Oncotype DX to predict the risk of breast cancer recurrence suggest that patients with ER-positive, node-negative breast cancer and a low recurrence score may need only adjuvant treatment with tamoxifen, while intermediate- and high-risk patients may require additional treatment with adjuvant chemotherapy. MammaPrint, an oligonucleotide microassay performed on fresh-frozen tumor samples, analyzes the expression of 70 genes. Studies have found that MammaPrint allows young patients (<61 years) with early-stage breast cancer to be categorized as having a high or low risk of distant metastasis. High-risk patients may then be managed with more aggressive therapy.
Conclusion: Two gene-expression assays, Oncotype DX and MammaPrint, have been developed to determine the risk of breast cancer recurrence in patients with stage I or II node-negative breast cancer. In the future, these tests may be useful in determining the need for systemic adjuvant therapy in such patients.