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). Here, IGKV6D-21 is linked to breast cancer.