SPHK1 and breast cancer: On the other hand, some pre-clinical studies of breast cancer have described the interactions between SPHK1 and numerous signaling targets which have been known as pivotal players in the regulation of breast CSCs, such as Notch, NF-κB, STAT3, EGFR, and MMPs (Lee et al., 2010; Kim et al., 2011; Marotta et al., 2011; Hirata et al., 2014; Nagahashi et al., 2018), suggesting that SPHK1 is as a potential functional target in breast CSCs.