SPHK1 and breast cancer: 3 × 105 ER-positive A. MCF7 and ER-negative B. HCC-1806 breast cancer cells were plated per well of a 6-well plate and cultured for 24 h and subsequently treated with the dual IGF1R/InsR dual tyrosine kinase inhibitor (OSI-906; 0.1, 0.4 and 1.6 μM) and/or SphK1 inhibitor (SKI-II; 4 μM) for 24 h.