USF1 and neoplasm: Transcriptional factors and signaling pathways frequently activated in tumor cells, like c-Myc, specific protein 1 (SP1), upstream transcription factor 1 (USF1), signal transducer and activator of transcription 3 (STAT3), phosphoinositide 3-kinase (PI3K), and nuclear factor of activated T-cells (NFAT), can positively stimulate hTERT promoter expression.