CXCR4 and cancer: Vimentin and CXCR4 are widely used to identify cell types within tumor cultures; co-staining differentiates vimentin-positive CXCR4-negative (VIM+/CXCR4−) presumptive fibroblasts from vimentin and CXCR4 co-expressing (VIM+/CXCR4+) presumptive cancer stem cells that have previously been reported to grow out in 3D Matrigel cultures [59,60].