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Impact of a 21-gene RT-PCR assay on treatment decisions in early-stage breast cancer.

Impact of a 21-gene RT-PCR assay on treatment decisions in early-stage breast cancer

Lyman GH, Cosler LE, Kuderer NM and Hornberger J

Cancer, 2007, 109, 1011-1016

This paper looks at use of the 21-gene RT-PCR assay (marketed in the USA as Oncotype DX) for prognostication and prediction in breast cancer, and its cost effectiveness. The assay has been developed using 21 genes selected from an exploratory set of 250, and genes are selected on the basis of their predictive ability, and the capacity for them to be extracted successfully for analysis from paraffin blocks rather than frozen tumour sections.

A score of between 1 and 100 is assigned to each tumour on the basis of the application of a proprietary algorithm to the level of expression in the RT-PCR assay for the 21 genes. A score of greater than 31 is defined as high risk, 18 to 31 as intermediate risk, and less than 18 as low risk. Paik et al. validated this protocol in a subset of 651 patients in the National Surgical Adjuvant Breast and Bowel Project (NSABP) B20 study [1]. Outcomes were better in the lower risk groups. In addition, patients in the NSABP B20 study were treated with tamoxifen, or tamoxifen plus chemotherapy, and the interaction of these treatments with outcome and with recurrence score was studied. Of the 651 patients for whom expression data were available, 64 (9.8%) developed distant recurrence, including 31 (13.7%) who received tamoxifen and 33 (7.8%) who received chemotherapy. Benefit of the chemotherapy was not distributed equally between the groups. Little absolute benefit was seen in either the low- or intermediate-risk groups, but a large effect was seen in the high-risk group. Distant recurrence was seen in the low-risk, intermediate-risk and high-risk groups in 3.7%, 17.8% and 38.3% of patients receiving tamoxifen alone, and in 5.0%, 10.1% and 11.1% of those receiving chemotherapy plus tamoxifen, respectively.

The paper discussed here compared application of three strategies: treating all comers with tamoxifen alone; treating all with tamoxifen plus chemotherapy; and treating those with an intermediate- or high-risk score with tamoxifen plus chemotherapy and those with a lower risk with tamoxifen alone. It is not surprising that treatment with tamoxifen alone was cheapest. A recurrence score-guided strategy was cheaper than a chemotherapy plus tamoxifen strategy for all but the most obsolete chemotherapy regimens (four cycles of doxorubicin/cyclophosphamide was cheaper).

Gene expression arrays are now entering the clinical trial arena. The Oncotype DX assay is being applied in a National Cancer Institute (NCI) study [Trial Assigning Individualized Options for Treatment Rx (TAILORx)] assigning women with lymph node-negative, oestrogen receptor-positive breast cancer to hormonal therapy if the recurrence score is less than 11, to combination chemotherapy and hormonal therapy where the score is greater than 25, and randomly assigning those with a score of 11-25 to either hormonal therapy or chemotherapy plus hormonal therapy. A similar strategy, utilising a different array, is being applied in the Microarray In Node negative Disease may Avoid Chemotherapy (MINDACT) study across Europe and in the UK.

Reference

[1.] Paik S, Shak S, Tang G et al. A multi-gene assay to predict recurrence of tamoxifen-treated, node-negative breast cancer. N Engl J Med, 2004, 351, 2817-2826.
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Author:Murray, Nick
Publication:Advances in Breast Cancer
Date:Jun 1, 2007
Words:544
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