Along with the findings reported by Sun et al. that BC patients with high IL-9 expression also tended to present high IL-9R expression30, we found co-cultured Th9 cells could upregulate IL-9R and SLC3A2 expression, but downregulate FKBP1A expression level in MCF7 cells (Fig. 6E), implying that Th9 cells might regulate the FKBP1A/SLC3A2 axis of BC cells via IL-9/IL-9R axis. This evidence concerns the gene SLC3A2 and breast cancer.