SPINK1 and Familial prostate cancer: Overexpression of miR-338-5p/miR-421 reduced ABCG2 transporter-mediated Hoechst 33,342 efflux in a side population analysis in prostate cancer, suggesting the potential modulation of SPINK1 in drug resistance [36], a finding proven by direct SPINK1 silencing using specific shRNA clones [37].