CD44 and neoplasm: To better understand the proteomic alterations and mechanistic regulation of self-renewal and tumor cluster formation, we conducted global mass spectrometry analyses of TNBC cells, including clustering and non-clustering PDX tumor cells (CD44+ and CD44− cells) as well as MDA-MB-231 cells of wild-type (WT) and CD44 KO, which pooled populations were generated via multiple guide RNAs and CRISPR-Cas9 technique (Liu et al., 2019).