Osteotropic MDA-MET breast cancer cells(3) were engineered to express high levels of wild-type heparanase (HPSE-High) or transfected with the empty vector (HPSE-Low).(12) In addition, MDA-MET cells expressing catalytically inactive heparanases designated M225 [mutated proton donor site of the active site (Glu225 to Ala225)] and M343 [mutated nucleophilic residue of the active site (Glu343 to Ala343)] were prepared. The gene discussed is HPSE; the disease is breast cancer.