PTK6 and breast cancer: It is possible that there are differences in DNA accessibility for HIF binding sites between MDA-MB-231 and MCF-7 cells, or that the stringency of the ChIP-seq data analysis pipeline described in [70] excluded ITGA6. We recently validated breast tumor kinase (BRK/PTK6) as a HIF-dependent gene highly expressed in basal breast cancers [36]; however, PTK6 was also not identified as a HIF-dependent gene in this ChIP-seq study [70].