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.