PTK6 and cancer: Variations in promoter activity may play a significant role in the transcriptional deregulation of individual tumors, as a substantial fraction of established cancer consensus genes (22.4% in O-PDX models and 31.1% in cell line models, including APOBEC3B, TGFBR2, PAX7, HOXA11, PDCD1LG2, PTK6, BCL11B, FAS, and MYC; (Additional file 2: Table S1) displayed heterogeneous promoter activities in the surveyed tumor models.