Our recent findings that Runx2 and AP-1 is an important regulator in GCT stromal cells [7], [9] and that PTHrP is expressed by this tumor in vivo[10], together with the fact that Runx2 and PTHrP regulate each other in a reciprocal fashion through Ihh pathway [11], [12], [13], suggest that PTHrP may be one of the possible upstream or downstream effectors of Runx2. The gene discussed is RUNX2; the disease is neoplasm.