The S100 gene family encode low molecular weight proteins implicated in cancer progression. In this study, we analyzed the expression of four S100 genes in one cohort of patients with breast cancer and 16 S100 genes in a second cohort. In both cohorts, the expression of S100A8 and S1009 mRNA level was elevated in high-grade compared to low-grade tumors and in estrogen receptor-negative compared to estrogen receptor-positive tumors. None of the S100 transcripts investigated were significantly associated with the presence of lymph node metastasis. Notably, multiple S100 genes, including S100A1, S100A2, S100A4, S100A6, S100A8, S100A9, S100A10, S100A11, and S100A14 were upregulated in basal-type breast cancers compared to non-basal types. Using Spearman's correlation analysis, several S100 transcripts correlated significantly with each other, the strongest correlation has been found between S100A8 and S100A9 (r = 0.889, P < 0.001, n = 295). Of the 16 S100 transcripts investigated, only S100A11 and S100A14 were significantly associated with patient outcome. Indeed, these two transcripts predicted outcome in the cohort of patients that did not receive systemic adjuvant therapy. Based on our findings, we conclude that the different S100 genes play varying roles in breast cancer progression. Specific S100 genes are potential targets for the treatment of basal-type breast cancers.