PDPN and neoplasm: It is well established that tumor cells grown in non-adherent conditions to form spheres are enriched in CSCs [175], and, although global podoplanin expression was reduced in A431 sphere-derived cells, fluorescence-activated cell sorting (FACS) analysis identified a subpopulation (about 5% cells) with high podoplanin expression that coincided with the side population (SP) characterized by efflux nuclear Hoechst fluorescent dye [176].