The Runt domain transcription factors, RUNX1, RUNX2 and RUNX3, are integral components of signaling cascades mediated by both TGF-β and bone morphogenetic proteins (BMPs) in several important biological systems. RUNX2 functions synergistically with Smad1 and Smad5 to regulate bone-specific genes when BMP induces osteogenesis. RUNX3, which has been mapped to locus 1p36, is a major tumor suppressor of gastric cancer and appears to be an important component of the TGF-β-induced tumor suppressor pathway. A possible relationship between the TGF-β-induced tumor-suppressor pathway and a postulated tumor suppressor gene on 1p36 must be examined.