In order to quantify and compare the mRNA expression amounts of each nAChR subunit among human breast cancer cell lines and the normal (nonmalignant) human breast cell lines, real-time quantitative fluorescent PCR were used to detect the mRNA expression level of α3, α4, α5, α7, α9, α10, β2, β3 and β4 nAChR subunits respectively (Figure 2). This evidence concerns the gene CHRNA4 and breast cancer.