CD44 and breast cancer: Recent single cell-resolution RNA sequencing data obtained from CTCs of patients with prostate and breast cancer may help gain insights into the expression of stem-like markers, specifically in cancer cells as they transit through the bloodstream, as CTCs isolated from these cancer patients were shown to express CD44. Moreover, 60 % of the CTCs profiled from prostate cancer patients were also enriched for ALDH7A1 and other putative stem-like markers such as KLF4 [7, 31].