To study the effects resulting from the inhibition of BSP synthesis and secretion, we generated MDA – MB – 231 breast cancer cell clones containing a tet-regulated expression cassette with a specific miRNA against BSP and used Flp-recombinase-mediated cassette exchange (RMCE) for introducing the gene cassette into a well-defined genomic locus. The gene discussed is IBSP; the disease is breast cancer.