PTK2 and cancer: Excision of floxed-fak upon a single treatment with 4-hydroxy-tamoxifen (4-OHT) resulted in complete FAK protein deficiency [29], [30] (see also Fig. 1C and 2B), which we could reverse by re-expressing wt FAK, allowing us to study how cancer cells cope with severe perturbation of the integrin/FAK signalling pathway.