Abstract: The present disclosure relates to the generation and uses of an improved set of biomarkers that are aryl hydrocarbon receptor (AHR) target genes, designated as “AHR biomarkers.” The AHR biomarkers described herein allow one to efficiently determine AHR activation groups and sub-groups, in particular for an improved classification of tumors. As used herein, AHR activation groups are called “AHR activation signatures”. The AHR biomarkers comprise markers that are important in diagnosis and therapy, for example for selecting patients for treatment with AHR activation modulating interventions, and monitoring of therapy response.