Supplementary Figures Suppl. Figure 1: Diagram of the analytical strategy and the flow of patients through the study according to REMARK criteria ("REporting recommendations for tumour MARKer prognostic studies" McShane et al. J Clin Oncol. 2005;23:9067). Suppl. Figure 2: A) ESR1 gene expression values in different age groups. The distribution of ESR1 mRNA expression as measured by Affymetrix probeset 205225_at is shown for patients in different age groups. The position of the ER negative peak in the bimodal distribution and the boundary representing the cutoff associated with ER status (black arrow) is conserved among all groups. In contrast, the median expression in the ER positive group (small red arrows) increases with age. B) Linear relationship between age and ESR1 gene expression in luminal subtypes. Scatter plots of ESR1 mRNA expression measured by Affymetrix probeset 205225_at and patients’ age at diagnosis are given separately for different subtypes of breast cancer. A linear smooth with confidence bounds was added to the plots using ggplot2 (Wickham H: ggplot2: Elegant graphics for data analysis. Dordrecht: Springer; 2009. [Use R!]. Supplementary Tables Supplementary Table 1: Datasets used in the study see file Suppl_Tab_S1.pdf Supplementary Table S2: Information and individual subtype assignments of all 4467 samples see file Suppl_Table_S2.xls Supplementary Table S3: Response to neoadjuvant chemotherapy according to age Subtype Age No pCR pCR total P-value Luminal A <40 y 12 0 12 1.0 ≥ 40 y 76 2 78 Luminal B <40 y 20 0 20 0.23 ≥ 40 y 119 16 135 HER2 <40 y 5 0 5 0.060 ≥ 40 y 20 19 39 TNBC <40 y 17 14 31 0.15 ≥ 40 y 100 46 146 Total <40 y 54 14 68 1.0 ≥ 40 y 315 83 398 all 369 97 466