CD274 and breast cancer: To elucidate the molecular mechanism underlying the PD-L1-mediated transcriptional suppression of FGFR3-TACC3 in luminal BC cells, we cloned the putative promoter region of FGFR3 (chr4: 1793293–1808867) containing the transcription starting site and exon 1/2, and examined promoter activity using a dual-luciferase assay (Fig. 6A).