Although additional in vivo studies, using xenografts and syngeneic mouse models, support the involvement of SK1 in breast cancer progression and metastasis [21, 24], there are no other reports assessing the role of SK1 in genetically engineered mouse models with spontaneous breast tumor initiation within the correct microenvironment from an otherwise normal mammary cell, and with an intact immune system. Here, SPHK1 is linked to breast cancer.