CD9 and breast cancer: A 20-gene combination, {COPA, GATA3, HDGF, LUM, SPINT2, STAT1, AEBP1, CALR, TRPS1, EPRS, ARL6IP1, EVL, RAD21, PKM2, CD9, NPNT, CLTC, CDH1, NAT1, SH3BGRL}, has been identified, which can distinguish breast cancer from all other cancers, achieving a 94.3% average level of discrimination, and breast cancer from control samples with 99.9% accuracy.