Correlation of microRNA-18a expression with HIF1A mRNA expression, hypoxia-responsive gene expression and distant metastasis in breast tumors. (A) Differential expression of microRNA-18a (miR-18a) and hypoxia-inducible factor 1α (HIF1A) mRNA in breast cancer subtypes. Expression data were retrieved from the Cancer Genome Atlas database. GE, Generalized estimating equation. (B) There was an inverse correlation between miR-18a and HIF1A mRNA expression in basal-like breast tumors. The basal-like breast tumors in four individual data sets were defined according to the PAM50 classifier. (C) Higher expression of HIF1A and hypoxia-responsive genes is associated with a shorter interval of distant metastasis–free survival (DMFS) of patients with basal-like breast tumors. Kaplan-Meier analysis was conducted using the GOBO program.