A new study has reported that risk of breast cancer increases with level of education. Breast cancer has been widely reported to be positively linked to education and other indicators of socioeconomic position. In fact, education is among the factors typically adjusted for when researchers calculate breast cancer risk. However, until now, this factor has not been examined in a twin study, where shared familial factors are adjusted for. The study included 16,310 twins, whose level of education and other factors were obtained from the Danish Twin Registry, the Danish Cancer Registry, and other official registries. Analyses were performed using both unpaired and intrapair data.

In the unpaired analysis (which ignored twinhood), an educational gradient in breast cancer risk was found, with higher levels of education corresponding to higher risk of breast cancer. Similar findings were observed in the intrapair analyses of all twins, although the results were no longer statistically significant. However ,when intrapair analyses were divided according to whether the twins were identical or fraternal, the effect of education was found to be lower in the identical twins. The authors conclude that their findings support an effect of education on breast cancer risk beyond shared familial factors.