Abstract: Provided are compositions, including kits, and methods comprising use of a biomarker ?3 integrin, including the ?v?3 integrin, for detecting circulating tumor cells (CTCs), tumor stem cells, extracellular vesicles (EV), including exosomes and microvesicles, that are released by CTCs or cancer cells, as well as the tumor from which the CTCs or EVs derive, and to make a patient prognosis, and to assess tumor progression, and drug resistance (for example, resistance to tyrosine kinase inhibitors), e.g., for several cancers including: breast, colon, lung and pancreatic cancers. In alternative embodiments, a patient fluid sample, e.g., a blood, serum, urine, CSF or other sample, is taken and used to detect cancer stem cells, EVs- and/or CTCs-comprising ?3 integrin and/or a ?v?3 integrin. Provided are compositions, including kits, and methods and uses of the biomarker ?3 integrin for anti-cancer drug design.