SDCBP and head and neck cancer: Interestingly, the A255V and V209I mutants of the MDA-9 PDZ2 domain, observed in patients with gastric or head and neck cancers (data from TCGA, PanCancer Atlas), also exhibited a reduced affinity (Kd > 5 mM) (Figure 3D,E), probably due to the induced steric repulsions.