To be able to separate the intracellular response from the effect of FGFR and downstream signaling pathways activation, we measured caspase 3/7 activity in two different FGFR1-expressing cell lines, mouse NIH 3T3 fibroblasts and human U2OSR1 osteosarcoma cells in the presence of a potent chemical FGFR inhibitor [28]. Here, FGFR1 is linked to osteosarcoma.