Abstract: The invention relates to the use of gene modifications in the human gene CHK2 (CHEK2), which encodes the checkpoint kinase 2, for predicting the risk and progression of cancer diseases, for predicting the response to pharmacological or non-pharmacological therapeutic measures for treating cancer diseases, and for predicting undesired effects of drugs. The invention further relates to the provision of individual gene variants with the help of which further gene modifications that can be used for the aforementioned purposes can be detected and validated. Such gene modifications can comprise a substitution of adenine for guanine in position -7161 in the promoter of CHK2, a substitution of guanine for cytosine in position -7235, a substitution of adenine for guanine in position -10532, or a deletion of 29 base pairs in positions -10621 to -10649.