AHR and neoplasm: Comparisons of AhR-expressing (AHR+/+) or AhR-deficient (AHR−/− or AHR−/+) mice in p53 knockout or p53 heterozygous backgrounds revealed that the loss of AhR results in greater tumor numbers, a broader tumor spectrum, and significantly reduced survival relative to their AhR-expressing or AhR heterozygous counterparts in p53-deficient backgrounds (p53−/− or p53+/−) (Figure 4).