The 70-gene prognosis-signature predicts disease outcome in breast cancer patients with 1-3 positive lymph nodes in an independent validation study

Purpose The 70-gene prognosis-signature has shown to be a valid prognostic tool in node-negative breast cancer. Although axillary lymph node status is considered to be one of the most important prognostic factors, still 25-30% of node-positive breast cancer patients will remain free of distant metastases, even without adjuvant systemic therapy. We therefore investigated whether the 70-gene prognosis-signature can accurately identify patients with 1-3 positive lymph nodes who have an excellent disease outcome. Methods Frozen tumour samples from 241 patients with operable T1-3 breast cancer, and 1-3 positive axillary lymph nodes, with a median follow-up of 7.8 years, were selected from 2 institutes. Using a customized microarray, tumour samples were analysed for the 70-gene tumour expression signature. In addition, we reanalysed part of a previously described cohort (n = 106) with extended follow-up. Results The 10-year distant metastasis-free (DMFS) and breast cancer specific survival (BCSS) probabilities were 91% (SE 4%) and 96% (SE 2%), respectively for the good prognosis-signature group (99 patients), and 76% (SE 4%) and 76% (SE 4%), respectively for the poor prognosis-signature group (142 patients). The 70-gene signature was significantly superior to the traditional prognostic factors in predicting BCSS with a multivariate hazard ratio (HR) of 7.17 (95% CI 1.81 to 28.43; P = 0.005). Conclusions The 70-gene prognosis-signature outperforms traditional prognostic factors in predicting disease outcome in patients with 1-3 positive nodes. Moreover, the signature can accurately identify patients with an excellent disease outcome in node-positive breast cancer, who may be safely spared adjuvant chemotherapy.