Cancer stem cells are implicated in tumor metastasis although the exact mechanisms remain poorly understood. The expression of cellular prion protein (PrPc), a highly conserved glycoprotein that has the same protein sequence as the scrapie prion protein, is positively correlated with an increased risk of metastasis in colorectal cancer. By double immunofluorescence staining of CD44 (green) and PrPc (red), CD44⁺PrPc⁺ cells were detected in the cryosections of colorectal cancers. PrPc⁺CD44⁺ colorectal cancer stem cells displayed high liver metastatic capability. For details, see article by Du and colleagues on page 2682.