Hyperactive MAPK signaling signature secreted in greater amounts by basal breast cancer CAFs compared to luminal breast cancer CAFs; signature includes overexpression of miR-221/222 in CAF- derived exosomes; CAF23BAS-exosomes caused up-regulation of hyperactive MAPK-mediated ER repression in ER+ breast cancer cells. This evidence concerns the gene ESR1 and breast carcinoma.