title: Letter: Two-stage transformation in vitro.
mesh_terms: D000818:Animals; D001580:Benzopyrenes; D002273:Carcinogens; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D002999:Clone Cells; D004224:Diterpenes; D004952:Esters; D005347:Fibroblasts; D051381:Rats
chemical_list: D001580:Benzopyrenes; D002273:Carcinogens; D004224:Diterpenes; D004952:Esters