In fact, the analysis of the total cancer cell mass by Hoechst 33342 dye efflux technique can detect a small fraction of cancer cells with stem cell-like properties designated as a side population (SP) that possesses a higher ability to actively efflux the fluorescent DNA-binding dye, Hoechst 33342 than the non-SP cell fraction due to its elevated expression levels of ATP-binding cassette (ABC) multidrug efflux pumps [1,175,176]. The gene discussed is ABCB6; the disease is cancer.