GSTA4 and skin neoplasm: The observation that C57BL/6.Psl1Bdba mice were relatively resistant to skin tumor promotion by TPA, even though they inherited the susceptibility alleles of Psl1.2a, Psl1.2b, and Gsta4 from DBA/2, suggests that a fourth gene mapping distal to D9Mit306 causes a decrease in skin tumor promotion susceptibility when inherited from DBA/2.