Indeed, TBX3 has been reported to directly repress p14ARF/p19ARF and our observation that p21 levels increase when TBX3 is depleted in the mouse chondrosarcoma ATDC5 cells, which do not express p53 [13], implies that TBX3 must also repress p21 independently of p19ARF-p53. This evidence concerns the gene CDKN1A and chondrosarcoma.