Breast cancer is the most frequent cancer among women in industrialized countries. It affects women in all parts of the world and it is therefore of the utmost importance to identify potential genetic and environmental factors in different ethnic populations.

Breast cancer is a multifactorial disease. Risk factors related to prolonged lifetime exposure to estrogens are extensively accepted. Moreover, environmental and lifestyle factors are anticipated to explain a large proportion of breast cancer cases. During recent years, genetic factors have also been shown to contribute to a large proportion of the breast cancer risk. In this sense, genetic factors signify mainly the high or low penetrance genes. Mutations in high penetrance genes are relatively rare and account for only 5-10% of breast cancer cases. Polymorphisms in low penetrance genes, on the other hand, pose a low risk at the individual level, but they are more common in the entire population. Therefore, the low penetrance genes, sometimes called modifier genes, acting together with endogenous/lifestyle/environmental risk factors, are likely to explain a higher proportion of breast cancer cases at the population level than the high penetrance genes.

In this work, the potential role of single nucleotide polymorphisms (SNPs) of certain low penetrance genes in relation to breast cancer risk was examined among Finnish study subjects. The selected genes encode proteins involved in xenobiotic and estrogen metabolism as well as in the detoxification of reactive oxygen species. The association between the polymorphic vitamin D receptor gene and the breast cancer risk was also investigated.