The FGFR3 gene has been shown to be subject to activating mutations and gene amplification leading to a variety of proliferative and developmental disorders depending on whether these events occur in the germline or arise somatically. As is the case for the other receptors, many of the activating mutations that are seen in FGFR3-related cancers mimic the germline FGFR3 mutations that give rise to autosomal skeletal disorders and include both ligand-dependent and independent mechanisms (reviewed in Webster and Donoghue, 1997; Burke et al, 1998; Wesche et al, 2011). In addition to activating mutations, the FGFR3 gene is subject to a translocation event in 15% of multiple myelomas (Avet-Loiseau et al, 1998; Chesi et al, 1997). This chromosomal rearrangement puts the FGFR3 gene under the control of the highly active IGH promoter and promotes overexpression and constitutive activation of FGFR3 (Otsuki et al, 1999). In a small proportion of multiple myelomas, the translocation event is accompanied by activating mutations in the FGFR3 coding sequence (Chesi et al, 1997; Onwuazor et al, 2003; Ronchetti et al, 2001).