CD9 and breast cancer: Palmitoylated and tetraspanin proteins present on the surface of exosomes secreted by breast cancer cells, as well as miRNAs (miR-195, miR-21, miR-484/191) and some proteins (CD9, CD63, CD81, CD24, p-selectin, survivin and its splice variants,) are differentially expressed in certain stages and types of breast cancer (BC) in the extracted exosomes.