It has been shown that 10 μM nicotine stimulates nAChRs (particularly α9-containing nAChRs) to induce proliferation in two breast cancer cell lines (MDA-MB 231 and MCF-7), and induces the growth of tumors xenografted into SCID mice (Lee et al., 2010). This evidence concerns the gene IGKV1D-22 and breast cancer.