ABCB4 and neoplasm: We have revealed strain-specificity of the effect of PHx on tumor acceleration in Mdr2-KO males operated at the age of six months: in the FVB/N strain, the tumor-promoting effect of PHx could be already detected at the age of nine months, whereas in the B6 strain, no effect of PHx on HCC development could be observed even at the age of 14 months.