Statistical interrogation of the GSE4922 microarray dataset of human primary breast cancers. Expression levels of Snail1 (A), Zeb1/δEF1 (C) and Snail2 (E) were compared between tumours from patients who remained disease-free and those from patients who had a disease-recurrence event (local, regional, distant or death from breast cancer) across the 242 patients with a non-zero disease-free survival time in the GSE4922 microarray dataset . Snail1 was expressed more highly in tumours from patients who had a disease-recurrence event, as determined by Mann-Whitney test (p = 0.017). Zeb1/δEF1 was expressed more highly in tumours from patients who remained disease-free, as determined by Mann-Whitney test (p = 0.026). Kaplan-Meier analysis of disease-free survival comparing patients with a Snail1 (B), Zeb1/δEF1 (D) or Snail2 (F) expression level above or below the mean expression level. Overall patients with an above mean Snail1 expression value had a poorer clinical outcome as determined by Gehan-Breslow-Wilcoxon test (p = 0.031), as did those patients with a below mean Zeb1/δEF1 expression value as determined by Gehan-Breslow-Wilcoxon test (p = 0.004).