KRT8 and prostate cancer: To further confirm the tumour origin of HBB, we used RNA in-situ hybridization (RNA-ISH) to directly visualize the cells expressing HBB. In blood samples from 5 patients with advanced prostate cancer (castrate-resistant or CRPC), 58 of 134 single CTCs and CTC-clusters that were positive for expression of EPCAM and/or KRT8/18/19 transcripts coexpressed HBB mRNA (Fig. 1d,e).